Revert "usb: phy: generic: Get the vbus supply"

This reverts commit 75fd6485cccef269ac9eb3b71cf56753341195ef.
This patch was applied twice by accident, causing probe failures.
Revert the accident.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Fixes: 75fd6485ccce ("usb: phy: generic: Get the vbus supply")
Cc: stable <stable@kernel.org>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20240314092628.1869414-1-alexander.stein@ew.tq-group.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Disable vbus on removal

If we enabled vbus, we need to balance that with a disable.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20240123225111.1629405-5-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Implement otg->set_vbus

Some USB controller drivers call otg_set_vbus when entering host or
device mode. Implement this callback so that VBUS can be turned on and
off automatically. This is especially useful when there is no property
for a VBUS supply in the controller's binding.

This results in a change in semantics of the vbus_draw regulator.
Whereas before it represented the VBUS supplied by an A-Device when we
acted as a B-Device, now it represents an internal VBUS source.
Accordingly, we no longer set the current limit or enable/disable the
bus from nop_gpio_vbus_thread. Because this supply was never initialized
before the previous commit, there should be no change in behavior.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20240123225111.1629405-4-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Get the vbus supply

While support for working with a vbus was added, the regulator was never
actually gotten (despite what was documented). Fix this by actually
getting the supply from the device tree.

Fixes: 7acc9973e3c4 ("usb: phy: generic: add vbus support")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20240123225111.1629405-3-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: add suspend support for regulator

Disable the vcc regulator on suspend and enable it on resume.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://lore.kernel.org/r/20231027122955.22123-1-francesco@dolcini.it
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Convert to platform remove callback returning void

The .remove() callback for a platform driver returns an int which makes
many driver authors wrongly assume it's possible to do error handling by
returning an error code. However the value returned is (mostly) ignored
and this typically results in resource leaks. To improve here there is a
quest to make the remove callback return void. In the first step of this
quest all drivers are converted to .remove_new() which already returns
void.

Trivially convert this driver from always returning zero in the remove
callback to the void returning variant.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20230319092428.283054-5-u.kleine-koenig@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Add wakeup capability

In case USB phy is the wakeup source, enable its wakeup
capability.

Signed-off-by: Li Jun <jun.li@nxp.com>
Link: https://lore.kernel.org/r/1666764742-4201-2-git-send-email-jun.li@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: make vcc regulator optional

phy-generic uses the existance of the property "vcc-supply" to see if a
regulator is optional or not. Use devm_regulator_get_optional() instead
which exists for this purpose. Using devm_regulator_get_optional()
avoids "supply vcc not found, using dummy regulator" messages.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20221012132754.292151-1-s.hauer@pengutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Switch to use dev_err_probe() helper

In the probe path, dev_err() can be replaced with dev_err_probe()
which will check if error code is -EPROBE_DEFER and prints the
error name. It also sets the defer probe reason which can be
checked later through debugfs. It's more simple in error path.

Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20220922133323.2135494-1-yangyingliang@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: generic: Get the vbus supply

While support for working with a vbus was added, the regulator was never
actually gotten (despite what was documented). Fix this by actually
getting the supply from the device tree.

Fixes: 7acc9973e3c4 ("usb: phy: generic: add vbus support")
Cc: stable <stable@kernel.org>
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20220425171412.1188485-3-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy-generic: Delete unused platform data

The last user of the phy generic platform data was
deleted in commit 1e041b6f313aaa966612a7e415cfc09c90d6b829
("usb: dwc3: exynos: Remove dead code"). So get rid of
the platform data, which rids us of another consumer of
the legacy GPIO API at the same time. Make sure we
only inlcude <linux/gpio/consumer.h> which is all we use.

Alter the usb_phy_gen_create_phy() function prototype to
not pass any platform data as this is just hardcoded to
NULL at all locations calling it in the kernel.

Move the devm_gpiod_get* calls out of the if (of_node)
parenthesis, as these calls are generic and do not depend
on device tree, they are used by any hardware description.

Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy-generic: Use gpiod_set_value_cansleep

The nop_reset and shutdown methods are called in a context that can sleep,
so use gpiod_set_value_cansleep instead of gpiod_set_value.

If you've connected the reset line to a GPIO expander, you'd get a kernel
"slowpath" warning with gpiod_set_value.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

USB: phy: Remove redundant license text

Now that the SPDX tag is in all USB files, that identifies the license
in a specific and legally-defined manner. So the extra GPL text wording
can be removed as it is no longer needed at all.

This is done on a quest to remove the 700+ different ways that files in
the kernel describe the GPL license text. And there's unneeded stuff
like the address (sometimes incorrect) for the FSF which is never
needed.

No copyright headers or other non-license-description text was removed.

Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

USB: add SPDX identifiers to all remaining files in drivers/usb/

It's good to have SPDX identifiers in all files to make it easier to
audit the kernel tree for correct licenses.

Update the drivers/usb/ and include/linux/usb* files with the correct
SPDX license identifier based on the license text in the file itself.
The SPDX identifier is a legally binding shorthand, which can be used
instead of the full boiler plate text.

This work is based on a script and data from Thomas Gleixner, Philippe
Ombredanne, and Kate Stewart.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

usb: phy: phy-generic: propagate clk_get error if clock is required

If the clock handle is given in the DT, it means the clock is required
for proper operation of the PHY. In that case a failure to obtain the
clock must be propagated to stop the driver from probing. This fixes
working with clocks, which request probe deferral.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

usb: phy: phy-generic: add the implementation of .set_suspend

Add clock operation at .set_suspend if the PHY has
suspend requirement, it can be benefit of power saving for
phy and the whole system (parent clock may also be disabled).

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

usb: phy: phy-generic: Check clk_prepare_enable() error

clk_prepare_enable() may fail, so we should better check its return
value and propagate it in the case of failure.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

usb: phy: generic: remove the vbus dependency

As the last known user, ie. pxa27x_udc relying on calls to
usb_gadget_xxx() was amended to use the phy notifier, remove a bit the
USB stack adherence.

Actually the driver still uses the gadget API for structures definition,
but the implementation of USB gadget specific function usb_gadget_*() is
not necessary anymore.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

usb: phy: generic: cope with initial state

In the gpio based case, the status of the phy is known at start by
reading the VBus gpio.

Actually, this is a fix, as this initial state, when not set up,
prevents a gadget to answer to the enumeration phase, as there is no
notification in this case (the VBus is already high when kernel boots)
so no interrupt is triggered, and the flow is :
- gadget initializes
- gadget gets its phy-generic with a xxx_get_phy_xxx() call type
- gadget does a "set_peripheral()" call type
=> here if the otg->state is correctly filled, the proper vbus
handling will be called, and the gadget will be aware it should
answer enumeration and go forth

Without this fix, the USB cable must be removed and replugged for any
gadget relying on phy-generic and its gpio vbus handling to work.

The problem was seen on a pxa27x architecture based board on a
devicetree build.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

usb: phy: generic: Handle late registration of gadget

It is possible for the VBUS detect GPIO interrupt to occur before
nop_set_peripheral() is called, in which case otg->gadget is NULL.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

usb: phy: phy-generic: Fix reset behaviour on legacy boot

The gpio-desc migration done in v4.0 caused a regression
with legacy boots due to reversed reset logic.
e.g. omap3-beagle USB host breaks on legacy boot.

Request the reset GPIO with GPIOF_ACTIVE_LOW flag so that
it matches the driver logic and pin behaviour.

Fixes: e9f2cefb0cdc ("usb: phy: generic: migrate to gpio_desc")
Cc: <stable@vger.kernel.org> # 4.0+
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: pass flags parameter to gpiod_get functions

Since 39b2bbe3d715 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for output.

Currently this parameter is made optional with the help of a cpp trick.
To allow dropping this hack convert callers to explictly pass a value
for flags.

Acked-by: Felipe Balbi <balbi@ti.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: pass flags parameter to gpiod_get functions

Since 39b2bbe3d715 (gpio: add flags argument to gpiod_get*() functions)
which appeared in v3.17-rc1, the gpiod_get* functions take an additional
parameter that allows to specify direction and initial value for output.

Currently this parameter is made optional with the help of a cpp trick.
To allow dropping this hack convert callers to explictly pass a value
for flags.

Acked-by: Felipe Balbi <balbi@ti.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

usb: phy: phy-generic: No need to call gpiod_direction_output() twice

Commit 9eb0797722895f4309b4 ("usb: phy: generic: fix the gpios to be optional")
calls gpiod_direction_output() in the probe function, so there is no need to
call it again, as we can simply call gpiod_set_value() directly.

Also, in usb_gen_phy_shutdown() we can simply put the GPIO directly in its
active level state and this allows us to simplify the nop_reset function to
treat only the reset case.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: phy-generic: Fix USB PHY gpio reset

Since commit e9f2cefb0cdc2ae ("usb: phy: generic: migrate to gpio_desc") a
kernel hang is observed on imx51-babbage board:

[ 1.392824] ci_hdrc ci_hdrc.1: doesn't support gadget
[ 1.397975] ci_hdrc ci_hdrc.1: EHCI Host Controller
[ 1.403205] ci_hdrc ci_hdrc.1: new USB bus registered, assigned bus number 1
[ 1.422335] ci_hdrc ci_hdrc.1: USB 2.0 started, EHCI 1.00
[ 1.432962] hub 1-0:1.0: USB hub found
[ 1.437119] hub 1-0:1.0: 1 port detected

This hang happens because the reset GPIO stays at logic level 0.

The USB PHY reset gpio is defined in the dts file as:

reset-gpios = <&gpio2 5 GPIO_ACTIVE_LOW>;

, which means it is active low, so what the gpio reset pin needs to do in this
case is the following:

- Go to logic level 0 to reset the USB PHY
- Stay at 0 for a bit
- Go back to logic level 1

When switching to gpiod API we need to following according to
Documentation/gpio/consumer.txt:

"The first thing a driver must do with a GPIO is setting its direction. If no
direction-setting flags have been given to gpiod_get*(), this is done by
invoking one of the gpiod_direction_*() functions:

int gpiod_direction_input(struct gpio_desc *desc)
int gpiod_direction_output(struct gpio_desc *desc, int value)"

Since no direction-setting flags have been given to devm_gpiod_get_optional()
in our case, we need to use gpiod_direction_output to comply with the gpiod API.

With this change the USB PHY reset performs a proper reset, the kernel boots
fine and USB host is functional.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: fix the vbus interrupt request

Declare the interrupt as "one shot" so that it is masked until the end
of the threaded handler. This prevents the irq core from spitting out an
error :
"Threaded irq requested with handler=NULL and !ONESHOT for irq 63"

This was introduced by commit "usb: phy: generic: add vbus support".

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: fix the gpios to be optional

All the gpios, ie. reset-gpios and vbus-detect-gpio, should be optional
and not prevent the driver from working. Fix the regression in the
behavior introduced by commit "usb: phy: generic: migrate to gpio_desc".

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: make GPIOs optional for the generic phy

The use of GPIOs should be optional for the generic phy, otherwise
the Altera SOCFPGA platform at least is broken.

Fixes breakage caused by a combination of e9f2cefb0cd "usb: phy:
generic: migrate to gpio_desc" and 135b3c4304d "usb: dwc2: platform:
add generic PHY framework support".

Reviewed-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: add vbus support

Add support for vbus detection and power supply. This code is more or
less stolen from phy-gpio-vbus-usb.c, and aims at providing a detection
mechanism for VBus (ie. usb cable plug) based on a GPIO line, and a
power supply activation which draws current from the VBus.

[ balbi@ti.com : fix build break ]

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: migrate to gpio_desc

Change internal gpio handling from integer gpios into gpio
descriptors. This change only addresses the internal API and
device-tree/ACPI, while the legacy platform data remains integer space
based.

This change is only build compile tested, and very prone to error. I
leave this comment for now in the commit message so that this patch gets
some testing as I'm pretty sure it's buggy.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: remove file names from heading comments

File names in the heading comments fell out of favor long ago, and these weren't
even changed when the drivers were moved from drivers/usb/otg/, so remove them
at last...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: rename phy to usb_phy in OTG

This patch prepares the introduction of the generic PHY support in the
USB OTG common functions. The USB PHY member of the OTG structure is
renamed to 'usb_phy' and modifications are done in all drivers accessing
it. Renaming this pointer will allow to keep the compatibility for USB
PHY drivers.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: move the OTG state from the USB PHY to the OTG structure

Before using the PHY framework instead of the USB PHY one, we need to
move the OTG state into another place, since it won't be available when
USB PHY isn't used. This patch moves the OTG state into the OTG
structure, and makes all the needed modifications in the drivers
using the OTG state.

[ balbi@ti.com : fix build regressions with phy-tahvo.c, musb_dsps.c,
phy-isp1301-omap, and chipidea's debug.c ]

Acked-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: drop owner assignment from platform_drivers

A platform_driver does not need to set an owner, it will be populated by the
driver core.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

usb: phy: generic: allow multiples calls to usb_phy_generic_register()

it's now very easy to return a platform_device pointer
and have the caller pass it as argument when calling
usb_phy_generic_unregister().

Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: rename <linux/usb/usb_phy_gen_xceiv.h> to <linux/usb/usb_phy_generic.h>

now that all functions match the driver name,
the only missing piece is to rename the header
file itself.

Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: rename usb_nop_xceiv to usb_phy_generic

no functional changes, just renaming the function
in order to make it slightly clearer what it should
be used for, also matching the driver name.

Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: gadget: only GPL drivers in the gadget and phy framework

We only support GPL drivers in the USB Gadget Framework,
it sounds correct to make all exported symbols GPL too.

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: initialize the notifier when add a new phy

We need to initialize the notifer before use it.

So lets initialize it when add a new phy device to
reduce the code redundancy.

Signed-off-by: Neil Zhang <zhangwm@marvell.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: phy-generic: fix return value check in usb_nop_xceiv_register()

In case of error, the function platform_device_register_simple() returns
ERR_PTR() and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: fix a compiler warning

Just because it annoys me.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy-generic: fix nop xceiv probe

Commit bd27fa44e13830d2baa278d5702e766380659cb3 (usb: phy: generic:
Don't use regulator framework for RESET line) introduced regression: All
users of usb_nop_xceiv_register() will fail because there is no platform
data and the default reset GPIO is 0 which is a valid GPIO. Fix that.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: fix how we find out about our resources

instead of having each user of generic phy find
out about its own resources and pass it to the
core layer, have th core layer itself figure that
out. It's as simple as moving a piece of code
around. This fixes a big regression caused during
the merge window where am335x-based platforms
wouldn't be able to probe their PHY driver.

Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: remove dead code

Commit [4d175f34: usb: phy: nop: Defer clock prepare until PHY init]
removed a goto reaching behind a “return ret” at the end of the function
thus removing the only possible way that statement could be reached, and
so rendering it a dead code. This commit cleans it up by removing said
dead code.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: generic: Don't use regulator framework for RESET line

Modelling the RESET line as a regulator supply wasn't a good idea
as it kind of abuses the regulator framework and also makes adaptation
code more complex.

Instead, manage the RESET gpio line directly in the driver. Update
the device tree binding information.

This also makes us easy to migrate to a dedicated GPIO RESET controller
whenever it becomes available.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: nop: Defer clock prepare until PHY init

Since we only enable the PHY clock on init and the PHY init and shutdown
does not occur in atomitc context there is no need to prepare the clock
before it is enabled. Move the clk_prepare() operations to go along
with the enables, allowing the clock to be fully idle when not in use.

Signed-off-by: Mark Brown <broonie@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: phy-generic: export init functions

This patch exports the mostly generic functions so they can be used from
other phy driver instead of duplicating the code.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>

usb: phy: rename nop_usb_xceiv => usb_phy_gen_xceiv

The "nop" driver isn't a do-nothing-stub but supports a couple functions
like clock on/off or is able to use a voltage regulator. This patch
simply renames the driver to "generic" since it is easy possible to
extend it by a simple function istead of writing a complete driver.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>