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Currently skl_pcode_try_request function doesn't properly handle return value it gets from snb_pcode_rw, but treats status != 0 as success, returning true, which basically doesn't allow to use retry/timeout mechanisms if PCode happens to be busy and returns EGAIN or some other status code not equal to 0. We saw this on real hw and also tried simulating this by always returning -EAGAIN from snb_pcode_rw for 6 times, which currently will just result in false success, while it should have tried until timeout is reached: [ 22.357729] i915 0000:00:02.0: [drm:intel_cdclk_dump_config [i915]] Changing CDCLK to 307200 kHz, VCO 614400 kHz, ref 38400 kHz, bypass 19200 kHz, voltage level 0 [ 22.357831] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 1 [ 22.357892] i915 0000:00:02.0: [drm:skl_pcode_request [i915]] Success, exiting [ 22.357936] i915 0000:00:02.0: [drm] ERROR Failed to inform PCU about cdclk change (err -11, freq 307200) We see en error because higher level api, still notices that status was wrong, however we still did try only once. We fix it by requiring _both_ the status to be 0 and request/reply match for success(true) and function should return failure(false) if either status turns out to be EAGAIN, EBUSY or whatever or reply/request masks do not match. So now we see this in the logs: [ 22.318667] i915 0000:00:02.0: [drm:intel_cdclk_dump_config [i915]] Changing CDCLK to 307200 kHz, VCO 614400 kHz, ref 38400 kHz, bypass 19200 kHz, voltage level 0 [ 22.318782] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 1 [ 22.318849] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 2 [ 22.319006] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 3 [ 22.319091] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 4 [ 22.319158] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 5 [ 22.319224] i915 0000:00:02.0: [drm:__snb_pcode_rw [i915]] Returning EAGAIN retry 6 Reviewed-by: Vinod Govindapillai <vinod.govindapillai@intel.com> Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20220408125200.9069-2-stanislav.lisovskiy@intel.com |
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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 Restructured Text 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.