History log of /linux-master/drivers/clk/pxa/clk-pxa.c
Revision Date Author Comments
# e9b6ea4e 05-May-2023 Maxime Ripard <mripard@kernel.org>

clk: pxa: Add a determine_rate hook

The PXA "CKEN" clock implements a mux with a set_parent hook, but
doesn't provide a determine_rate implementation.

This is a bit odd, since set_parent() is there to, as its name implies,
change the parent of a clock. However, the most likely candidates to
trigger that parent change are either the assigned-clock-parents device
tree property or a call to clk_set_rate(), with determine_rate()
figuring out which parent is the best suited for a given rate.

The other trigger would be a call to clk_set_parent(), but it's far less
used, and it doesn't look like there's any obvious user for that clock.

Similarly, it doesn't look like the device tree using that clock driver
uses any of the assigned-clock properties on that clock.

So, the set_parent hook is effectively unused, possibly because of an
oversight. However, it could also be an explicit decision by the
original author to avoid any reparenting but through an explicit call to
clk_set_parent().

The latter case would be equivalent to setting the determine_rate
implementation to clk_hw_determine_rate_no_reparent(). Indeed, if no
determine_rate implementation is provided, clk_round_rate() (through
clk_core_round_rate_nolock()) will call itself on the parent if
CLK_SET_RATE_PARENT is set, and will not change the clock rate
otherwise.

And if it was an oversight, then we are at least explicit about our
behavior now and it can be further refined down the line.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20221018-clk-range-checks-fixes-v4-30-971d5077e7d2@cerno.tech
Signed-off-by: Stephen Boyd <sboyd@kernel.org>


# 117a1542 07-Apr-2022 Xiaoke Wang <xkernel.wang@foxmail.com>

clk: pxa: add a check for the return value of kzalloc()

kzalloc() is a memory allocation function which can return NULL when
some internal memory errors happen. So it is better to check it to
prevent potential wrong memory access.

Signed-off-by: Xiaoke Wang <xkernel.wang@foxmail.com>
Link: https://lore.kernel.org/r/tencent_2B9817738F38B02844C245946EFF3B407E09@qq.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>


# 3c816d95 18-Sep-2019 Arnd Bergmann <arnd@arndb.de>

ARM: pxa: move clk register definitions to driver

The clock register definitions are now used (almost) exclusively in the
clk driver, and that relies on no other mach/*.h header files any more.

Remove the dependency on mach/pxa*-regs.h by addressing the registers
as offsets from a void __iomem * pointer, which is either passed from
a board file, or (for the moment) ioremapped at boot time from a hardcoded
address in case of DT (this should be moved into the DT of course).

Cc: linux-clk@vger.kernel.org
Acked-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>


# fd13f811 18-Sep-2019 Arnd Bergmann <arnd@arndb.de>

ARM: pxa: move smemc register access from clk to platform

The get_sdram_rows() and get_memclkdiv() helpers need smemc
register that are separate from the clk registers, move
them out of the clk driver, and use an extern declaration
instead.

Cc: Michael Turquette <mturquette@baylibre.com>
Cc: Stephen Boyd <sboyd@kernel.org>
Cc: linux-clk@vger.kernel.org
Link: https://lore.kernel.org/lkml/87pnielzo4.fsf@belgarion.home/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>


# b886d83c 01-Jun-2019 Thomas Gleixner <tglx@linutronix.de>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 441

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation version 2 of the license

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-only

has been chosen to replace the boilerplate/reference in 315 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Armijn Hemel <armijn@tjaldur.nl>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190531190115.503150771@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>


# 62e59c4e 18-Apr-2019 Stephen Boyd <sboyd@kernel.org>

clk: Remove io.h from clk-provider.h

Now that we've gotten rid of clk_readl() we can remove io.h from the
clk-provider header and push out the io.h include to any code that isn't
already including the io.h header but using things like readl/writel,
etc.

Found with this grep:

git grep -l clk-provider.h | grep '.c$' | xargs git grep -L 'linux/io.h' | \
xargs git grep -l \
-e '\<__iowrite32_copy\>' --or \
-e '\<__ioread32_copy\>' --or \
-e '\<__iowrite64_copy\>' --or \
-e '\<ioremap_page_range\>' --or \
-e '\<ioremap_huge_init\>' --or \
-e '\<arch_ioremap_pud_supported\>' --or \
-e '\<arch_ioremap_pmd_supported\>' --or \
-e '\<devm_ioport_map\>' --or \
-e '\<devm_ioport_unmap\>' --or \
-e '\<IOMEM_ERR_PTR\>' --or \
-e '\<devm_ioremap\>' --or \
-e '\<devm_ioremap_nocache\>' --or \
-e '\<devm_ioremap_wc\>' --or \
-e '\<devm_iounmap\>' --or \
-e '\<devm_ioremap_release\>' --or \
-e '\<devm_memremap\>' --or \
-e '\<devm_memunmap\>' --or \
-e '\<__devm_memremap_pages\>' --or \
-e '\<pci_remap_cfgspace\>' --or \
-e '\<arch_has_dev_port\>' --or \
-e '\<arch_phys_wc_add\>' --or \
-e '\<arch_phys_wc_del\>' --or \
-e '\<memremap\>' --or \
-e '\<memunmap\>' --or \
-e '\<arch_io_reserve_memtype_wc\>' --or \
-e '\<arch_io_free_memtype_wc\>' --or \
-e '\<__io_aw\>' --or \
-e '\<__io_pbw\>' --or \
-e '\<__io_paw\>' --or \
-e '\<__io_pbr\>' --or \
-e '\<__io_par\>' --or \
-e '\<__raw_readb\>' --or \
-e '\<__raw_readw\>' --or \
-e '\<__raw_readl\>' --or \
-e '\<__raw_readq\>' --or \
-e '\<__raw_writeb\>' --or \
-e '\<__raw_writew\>' --or \
-e '\<__raw_writel\>' --or \
-e '\<__raw_writeq\>' --or \
-e '\<readb\>' --or \
-e '\<readw\>' --or \
-e '\<readl\>' --or \
-e '\<readq\>' --or \
-e '\<writeb\>' --or \
-e '\<writew\>' --or \
-e '\<writel\>' --or \
-e '\<writeq\>' --or \
-e '\<readb_relaxed\>' --or \
-e '\<readw_relaxed\>' --or \
-e '\<readl_relaxed\>' --or \
-e '\<readq_relaxed\>' --or \
-e '\<writeb_relaxed\>' --or \
-e '\<writew_relaxed\>' --or \
-e '\<writel_relaxed\>' --or \
-e '\<writeq_relaxed\>' --or \
-e '\<readsb\>' --or \
-e '\<readsw\>' --or \
-e '\<readsl\>' --or \
-e '\<readsq\>' --or \
-e '\<writesb\>' --or \
-e '\<writesw\>' --or \
-e '\<writesl\>' --or \
-e '\<writesq\>' --or \
-e '\<inb\>' --or \
-e '\<inw\>' --or \
-e '\<inl\>' --or \
-e '\<outb\>' --or \
-e '\<outw\>' --or \
-e '\<outl\>' --or \
-e '\<inb_p\>' --or \
-e '\<inw_p\>' --or \
-e '\<inl_p\>' --or \
-e '\<outb_p\>' --or \
-e '\<outw_p\>' --or \
-e '\<outl_p\>' --or \
-e '\<insb\>' --or \
-e '\<insw\>' --or \
-e '\<insl\>' --or \
-e '\<outsb\>' --or \
-e '\<outsw\>' --or \
-e '\<outsl\>' --or \
-e '\<insb_p\>' --or \
-e '\<insw_p\>' --or \
-e '\<insl_p\>' --or \
-e '\<outsb_p\>' --or \
-e '\<outsw_p\>' --or \
-e '\<outsl_p\>' --or \
-e '\<ioread8\>' --or \
-e '\<ioread16\>' --or \
-e '\<ioread32\>' --or \
-e '\<ioread64\>' --or \
-e '\<iowrite8\>' --or \
-e '\<iowrite16\>' --or \
-e '\<iowrite32\>' --or \
-e '\<iowrite64\>' --or \
-e '\<ioread16be\>' --or \
-e '\<ioread32be\>' --or \
-e '\<ioread64be\>' --or \
-e '\<iowrite16be\>' --or \
-e '\<iowrite32be\>' --or \
-e '\<iowrite64be\>' --or \
-e '\<ioread8_rep\>' --or \
-e '\<ioread16_rep\>' --or \
-e '\<ioread32_rep\>' --or \
-e '\<ioread64_rep\>' --or \
-e '\<iowrite8_rep\>' --or \
-e '\<iowrite16_rep\>' --or \
-e '\<iowrite32_rep\>' --or \
-e '\<iowrite64_rep\>' --or \
-e '\<__io_virt\>' --or \
-e '\<pci_iounmap\>' --or \
-e '\<virt_to_phys\>' --or \
-e '\<phys_to_virt\>' --or \
-e '\<ioremap_uc\>' --or \
-e '\<ioremap\>' --or \
-e '\<__ioremap\>' --or \
-e '\<iounmap\>' --or \
-e '\<ioremap\>' --or \
-e '\<ioremap_nocache\>' --or \
-e '\<ioremap_uc\>' --or \
-e '\<ioremap_wc\>' --or \
-e '\<ioremap_wc\>' --or \
-e '\<ioremap_wt\>' --or \
-e '\<ioport_map\>' --or \
-e '\<ioport_unmap\>' --or \
-e '\<ioport_map\>' --or \
-e '\<ioport_unmap\>' --or \
-e '\<xlate_dev_kmem_ptr\>' --or \
-e '\<xlate_dev_mem_ptr\>' --or \
-e '\<unxlate_dev_mem_ptr\>' --or \
-e '\<virt_to_bus\>' --or \
-e '\<bus_to_virt\>' --or \
-e '\<memset_io\>' --or \
-e '\<memcpy_fromio\>' --or \
-e '\<memcpy_toio\>'

I also reordered a couple includes when they weren't alphabetical and
removed clk.h from kona, replacing it with clk-provider.h because
that driver doesn't use clk consumer APIs.

Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Acked-by: Tero Kristo <t-kristo@ti.com>
Acked-by: Sekhar Nori <nsekhar@ti.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Mark Brown <broonie@kernel.org>
Cc: Chris Zankel <chris@zankel.net>
Acked-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: John Crispin <john@phrozen.org>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>


# 5fc6eb7d 26-Oct-2018 Julia Lawall <Julia.Lawall@lip6.fr>

clk: pxa: constify clk_ops structures

These clk_ops structures are only passed to a call to
clk_register_composite where the corresponding parameters
are const, so the clk_ops structure can be const as well.

Identified and transformed using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>


# c82a2cb8 15-Sep-2017 Arnd Bergmann <arnd@arndb.de>

clk: pxa: fix building on older compilers

gcc-4.4 got confused by the inline assembler statement:

drivers/clk/pxa/clk-pxa.c: In function 'pxa2xx_core_turbo_switch':
drivers/clk/pxa/clk-pxa.c:152: error: expected string literal before ')' token

This removes the extraneous ':' to let all compilers parse the
driver correctly.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>


# 84558ff7 08-Nov-2016 Stephen Boyd <sboyd@codeaurora.org>

clk: pxa: Use __iomem properly and staticize lock variable

This function is passed an __iomem pointer but we use a u32
pointer instead which makes checkers like spare complain.
Furthermore, "lock" is a pretty poor variable name for a string
that will go into lockdep reports and the symbol isn't marked
static. Cleanup all this.

Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>


# 2517b32b 08-Nov-2016 Arnd Bergmann <arnd@arndb.de>

clk: pxa: fix pxa2xx_determine_rate return

The new pxa2xx_determine_rate() function seems lacking in a few
regards:

- For an exact match or no match at all, the rate is uninitialized
as reported by gcc -Wmaybe-unintialized:
drivers/clk/pxa/clk-pxa.c: In function 'pxa2xx_determine_rate':
drivers/clk/pxa/clk-pxa.c:243:5: error: 'rate' may be used uninitialized in this function

- If we get a non-exact match, the req->rate output is never set
to the actual rate but remains at the requested rate.

- We should not attempt to print a rate if none could be found

This rewrites the logic accordingly.

Fixes: 9fe694295098 ("clk: pxa: transfer CPU clock setting from pxa2xx-cpufreq")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>


# 9fe69429 02-Nov-2016 Robert Jarzmik <robert.jarzmik@free.fr>

clk: pxa: transfer CPU clock setting from pxa2xx-cpufreq

This is the initial stage to transfer the pxa25x and pxa27x CPU clocks
handling from cpufreq to the clock API. More precisely, the clocks
transferred are :
- cpll : core pll, known also as the CPU core turbo frequency
- core : core, known also as the CPU actual frequency, being either the
CPU core turbo frequency or the CPU core run frequency

This transfer is a prequel to shrink the code in pxa2xx-cpufreq.c, so
that it can become, at least in devicetree builds, the casual cpufreq-dt
driver.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>


# 4e907ef6 12-Feb-2015 Javier Martinez Canillas <javier@osg.samsung.com>

clk: Replace explicit clk assignment with __clk_hw_set_clk

The change in the clk API to return a per-user clock instance, moved
the clock state to struct clk_core so now the struct clk_hw .core field
is used instead of .clk for most operations.

So for hardware clocks that needs to share the same clock state, both
the .core and .clk pointers have to be assigned but currently only the
.clk is set. This leads to NULL pointer dereference when the operations
try to access the hw clock .core. For example, the composite clock rate
and mux components didn't have a .core set which leads to this error:

Unable to handle kernel NULL pointer dereference at virtual address 00000034
pgd = c0004000
[00000034] *pgd=00000000
Internal error: Oops: 5 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.19.0-next-20150211-00002-g1fb7f0e1150d #423
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
task: ee480000 ti: ee488000 task.ti: ee488000
PC is at clk_mux_determine_rate_flags+0x14/0x19c
LR is at __clk_mux_determine_rate+0x24/0x2c
pc : [<c03a355c>] lr : [<c03a3734>] psr: a0000113
sp : ee489ce8 ip : ee489d84 fp : ee489d84
r10: 0000005c r9 : 00000001 r8 : 016e3600
r7 : 00000000 r6 : 00000000 r5 : ee442200 r4 : ee440c98
r3 : ffffffff r2 : 00000000 r1 : 016e3600 r0 : ee440c98
Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment kernel
Control: 10c5387d Table: 4000406a DAC: 00000015
Process swapper/0 (pid: 1, stack limit = 0xee488210)
Stack: (0xee489ce8 to 0xee48a000)
9ce0: 00000000 ffffffff 60000113 ee440c98 ee442200 00000000
9d00: 016e3600 ffffffff 00000001 0000005c ee489d84 c03a3734 ee489d80 ee489d84
9d20: 00000000 c048b130 00000400 c03a5798 ee489d80 ee489d84 c0607f60 ffffffea
9d40: 00000001 00000001 ee489d5c c003f844 c06e3340 ee402680 ee440d0c ed935000
9d60: 016e3600 00000003 00000001 0000005c eded3700 c03a11a0 ee489d80 ee489d84
9d80: 016e3600 ee402680 c05b413a eddc9900 016e3600 c03a1228 00000000 ffffffff
9da0: ffffffff eddc9900 016e3600 c03a1c1c ffffffff 016e3600 ed8c6710 c03d6ce4
9dc0: eded3400 00000000 00000000 c03c797c 00000001 0000005c eded3700 eded3700
9de0: 000005e0 00000001 0000005c c03db8ac c06e7e54 c03c8f08 00000000 c06e7e64
9e00: c06b6e74 c06e7f64 000005e0 c06e7df8 c06e5100 00000000 c06e7e6c c06e7f54
9e20: 00000000 00000000 eebd9550 00000000 c06e7da0 c06e7e54 ee7b5010 c06e7da0
9e40: eddc9690 c06e7db4 c06b6e74 00000097 00000000 c03d4398 00000000 ee7b5010
9e60: eebd9550 c06e7da0 00000000 c03db824 ee7b5010 fffffffe c06e7db4 c0299c7c
9e80: ee7b5010 c072a05c 00000000 c0298858 ee7b5010 c06e7db4 ee7b5044 00000000
9ea0: eddc9580 c0298a04 c06e7db4 00000000 c0298978 c02971d4 ee405c78 ee732b40
9ec0: c06e7db4 eded3800 c06d6738 c0298044 c0608300 c06e7db4 00000000 c06e7db4
9ee0: 00000000 c06beb58 c06beb58 c0299024 00000000 c068dd00 00000000 c0008944
9f00: 00000038 c049013c ee462200 c0711920 ee480000 60000113 c06c2cb0 00000000
9f20: 00000000 c06c2cb0 60000113 00000000 ef7fcafc 00000000 c0640194 c00389ec
9f40: c05ec3a8 c063f824 00000006 00000006 c06c2c50 c0696444 00000006 c0696424
9f60: c06ee1c0 c066b588 c06b6e74 00000097 00000000 c066bd44 00000006 00000006
9f80: c066b588 c003d684 00000000 c0481938 00000000 00000000 00000000 00000000
9fa0: 00000000 c0481940 00000000 c000e680 00000000 00000000 00000000 00000000
9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[<c03a355c>] (clk_mux_determine_rate_flags) from [<c03a3734>] (__clk_mux_determine_rate+0x24/0x2c)
[<c03a3734>] (__clk_mux_determine_rate) from [<c03a5798>] (clk_composite_determine_rate+0xbc/0x238)
[<c03a5798>] (clk_composite_determine_rate) from [<c03a11a0>] (clk_core_round_rate_nolock+0x5c/0x9c)
[<c03a11a0>] (clk_core_round_rate_nolock) from [<c03a1228>] (__clk_round_rate+0x38/0x40)
[<c03a1228>] (__clk_round_rate) from [<c03a1c1c>] (clk_round_rate+0x20/0x38)
[<c03a1c1c>] (clk_round_rate) from [<c03d6ce4>] (max98090_dai_set_sysclk+0x34/0x118)
[<c03d6ce4>] (max98090_dai_set_sysclk) from [<c03c797c>] (snd_soc_dai_set_sysclk+0x38/0x80)
[<c03c797c>] (snd_soc_dai_set_sysclk) from [<c03db8ac>] (snow_late_probe+0x24/0x48)
[<c03db8ac>] (snow_late_probe) from [<c03c8f08>] (snd_soc_register_card+0xf04/0x1070)
[<c03c8f08>] (snd_soc_register_card) from [<c03d4398>] (devm_snd_soc_register_card+0x30/0x64)
[<c03d4398>] (devm_snd_soc_register_card) from [<c03db824>] (snow_probe+0x68/0xcc)
[<c03db824>] (snow_probe) from [<c0299c7c>] (platform_drv_probe+0x48/0x98)
[<c0299c7c>] (platform_drv_probe) from [<c0298858>] (driver_probe_device+0x114/0x234)
[<c0298858>] (driver_probe_device) from [<c0298a04>] (__driver_attach+0x8c/0x90)
[<c0298a04>] (__driver_attach) from [<c02971d4>] (bus_for_each_dev+0x54/0x88)
[<c02971d4>] (bus_for_each_dev) from [<c0298044>] (bus_add_driver+0xd8/0x1cc)
[<c0298044>] (bus_add_driver) from [<c0299024>] (driver_register+0x78/0xf4)
[<c0299024>] (driver_register) from [<c0008944>] (do_one_initcall+0x80/0x1d0)
[<c0008944>] (do_one_initcall) from [<c066bd44>] (kernel_init_freeable+0x10c/0x1d8)
[<c066bd44>] (kernel_init_freeable) from [<c0481940>] (kernel_init+0x8/0xe4)
[<c0481940>] (kernel_init) from [<c000e680>] (ret_from_fork+0x14/0x34)
Code: e24dd00c e5907000 e1a08001 e88d000c (e5970034)

The changes were made using the following cocinelle semantic patch:

@i@
@@

@depends on i@
identifier dst;
@@

- dst->clk = hw->clk;
+ __clk_hw_set_clk(dst, hw);

@depends on i@
identifier dst;
@@

- dst->hw.clk = hw->clk;
+ __clk_hw_set_clk(&dst->hw, hw);

Fixes: 035a61c314eb3 ("clk: Make clk API return per-user struct clk instances")
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Michael Turquette <mturquette@linaro.org>


# 6f8a444a 06-Oct-2014 Robert Jarzmik <robert.jarzmik@free.fr>

clk: pxa: keep clocks initialization separated per variant

Have each pxa variant (pxa25x, pxa27x, pxa3xx) have its own device-tree
clock initializing function, to be able to register its own specific
core clocks.

Apply that change specifically to pxa27x.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Michael Turquette <mturquette@linaro.org>


# 14dd5b01 06-Oct-2014 Robert Jarzmik <robert.jarzmik@free.fr>

clk: pxa: declare init function and data __init

As the clock descriptions are constant and only usefull at init time,
mark them as such by :
- spliting clock description (desc) and clock private data (dynamic)
- mark __initdata clock descriptions

This makes all the register and descriptions of the clocks to go after
kernel init phase.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Michael Turquette <mturquette@linaro.org>


# bda00303 30-Jul-2014 Robert Jarzmik <robert.jarzmik@free.fr>

clk: add pxa clocks infrastructure

Add a the common code used by all PXA variants.

This is the first step in the transition from architecture defined
clocks (in arch/arm/mach-pxa) towards clock framework. The goal is to
have the same features (and not all the features) of the existing
clocks, and enable the transition of PXA to device-tree.

All PXA rely on a "CKEN" type clock, which :
- has a gate (bit in CKEN register)
- is generated from a PLL, generally divided
- has an alternate low power clock

Each variant will specialize the CKEN clock :
- pxa25x have no low power clock
- pxa27x in low power use always the 13 MHz ring oscillator
- pxa3xx in low power have specific dividers for each clock

The device-tree provides a list of CLK_* (ex: CLK_USB or CLK_I2C) to get
a handle on the clock. While pxa-clock.h will describe all the clocks of
all the variants, each variant will only use a subset of it.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Mike Turquette <mturquette@linaro.org>