coresight: tmc: Make etr buffer mode user configurable from sysfs

Currently TMC-ETR automatically selects the buffer mode from all available
methods in the following sequentially fallback manner - also in that order.

1. FLAT mode with or without IOMMU
2. TMC-ETR-SG (scatter gather) mode when available
3. CATU mode when available

But this order might not be ideal for all situations. For example if there
is a CATU connected to ETR, it may be better to use TMC-ETR scatter gather
method, rather than CATU. But hard coding such order changes will prevent
us from testing or using a particular mode. This change provides following
new sysfs tunables for the user to control TMC-ETR buffer mode explicitly,
if required. This adds following new sysfs files for buffer mode selection
purpose explicitly in the user space.

/sys/bus/coresight/devices/tmc_etr<N>/buf_modes_available
/sys/bus/coresight/devices/tmc_etr<N>/buf_mode_preferred

$ cat buf_modes_available
auto flat tmc-sg catu ------------------> Supported TMC-ETR buffer modes

$ echo catu > buf_mode_preferred -------> Explicit buffer mode request

But explicit user request has to be within supported ETR buffer modes only.
These sysfs interface files are exclussive to ETR, and hence these are not
available for other TMC devices such as ETB or ETF etc.

A new auto' mode (i.e ETR_MODE_AUTO) has been added to help fallback to the
existing default behaviour, when user provided preferred buffer mode fails.
ETR_MODE_FLAT and ETR_MODE_AUTO are always available as preferred modes.

Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
[Fixup year in sysfs ABI documentation]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230818082112.554638-1-anshuman.khandual@arm.com

docs: ABI: change read/write attributes

Unfortunately, (R) and (W) are valid markups for enumerated
lists, as described at:
https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#enumerated-lists

So, we ned to replace them by:

(R) -> (Read)
(W) -> (Write)

As otherwise, (R) will be displayed as R., with is not what
it is desired.

There's no need to touch (RO) and (RW).

Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/6e81ad8064f3ed4f8dc265086fdf1c618043f935.1604042072.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

coresight: tmc: Add configuration support for trace buffer size

Now that we can dynamically switch between contiguous memory and
SG table depending on the trace buffer size, provide the support
for selecting an appropriate buffer size.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

coresight: tmc: adding sysFS management entries

Adding management registers that convey implementation
specific characteristics. Those are useful for trace
configuration and collection along with general trouble
shooting.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

coresight: Adding ABI documentation

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>