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Timur Kristóf d251d54a26 drm/amd/pm: Increase SMC timeout on SI and warn (v3) 
[ Upstream commit 813d13524a ]

The SMC can take an excessive amount of time to process some
messages under some conditions.

Background:
Sending a message to the SMC works by writing the message into
the mmSMC_MESSAGE_0 register and its optional parameter into
the mmSMC_SCRATCH0, and then polling mmSMC_RESP_0. Previously
the timeout was AMDGPU_MAX_USEC_TIMEOUT, ie. 100 ms.

Increase the timeout to 200 ms for all messages and to 1 sec for
a few messages which I've observed to be especially slow:
PPSMC_MSG_NoForcedLevel
PPSMC_MSG_SetEnabledLevels
PPSMC_MSG_SetForcedLevels
PPSMC_MSG_DisableULV
PPSMC_MSG_SwitchToSwState

This fixes the following problems on Tahiti when switching
from a lower clock power state to a higher clock state, such
as when DC turns on a display which was previously turned off.

* si_restrict_performance_levels_before_switch would fail
  (if the user previously forced high clocks using sysfs)
* si_set_sw_state would fail (always)

It turns out that both of those failures were SMC timeouts and
that the SMC actually didn't fail or hang, just needs more time
to process those.

Add a warning when there is an SMC timeout to make it easier to
identify this type of problem in the future.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-11-13 15:37:11 -05:00
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README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.