Re: [PATCH v8] drm/i915/gen9: Fix PCODE polling during CDCLK change notification

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Jan 12, 2017 at 03:22:38PM +0200, Imre Deak wrote:
> commit 848496e5902833600f7992f4faa82dc1546051ba
> Author: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> Date:   Wed Jul 13 16:32:03 2016 +0300
> 
>     drm/i915: Wait up to 3ms for the pcu to ack the cdclk change request on SKL
> 
> increased the timeout to match the spec, but we still see a timeout on
> at least one SKL. A CDCLK change request following the failed one will
> succeed nevertheless.
> 
> I could reproduce this problem easily by running kms_pipe_crc_basic in a
> loop. In all failure cases _wait_for() was pre-empted for >3ms and so in
> the worst case - when the pre-emption happened right after calculating
> timeout__ in _wait_for() - we called skl_cdclk_wait_for_pcu_ready() only
> once which failed and so _wait_for() timed out. As opposed to this the
> spec says to keep retrying the request for at most a 3ms period.
> 
> To fix this send the first request explicitly to guarantee that there is
> 3ms between the first and last request. Though this matches the spec, I
> noticed that in rare cases this can still time out if we sent only a few
> requests (in the worst case 2) _and_ PCODE is busy for some reason even
> after a previous request and a 3ms delay. To work around this retry the
> polling with pre-emption disabled to maximize the number of requests.
> Also increase the timeout to 10ms to account for interrupts that could
> reduce the number of requests. With this change I couldn't trigger
> the problem.
> 
> v2:
> - Use 1ms poll period instead of 10us. (Chris)
> v3:
> - Poll with pre-emption disabled to increase the number of request
>   attempts. (Ville, Chris)
> - Factor out a helper to poll, it's also needed by the next patch.
> v4:
> - Pass reply_mask, reply to skl_pcode_request(), instead of assuming the
>   reply is generic. (Ville)
> v5:
> - List the request specific timeout values as code comment. (Ville)
> v6:
> - Try the poll first with preemption enabled.
> - Add code comment about first request being queued by PCODE. (Art)
> - Add timeout_base_ms argument. (Ville)
> v7:
> - Clarify code comment about first queued request. (Chris)
> v8:
> - Rebased on 4.9.2
> 
> Cc: Ville Syrj�l� <ville.syrjala@linux.intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Art Runyan <arthur.j.runyan@intel.com>
> Cc: <stable@vger.kernel.org> # v4.2- : 3b2c171 : drm/i915: Wait up to 3ms
> Cc: <stable@vger.kernel.org> # v4.2-
> Fixes: 5d96d8afcfbb ("drm/i915/skl: Deinit/init the display at suspend/resume")
> Reference: https://bugs.freedesktop.org/show_bug.cgi?id=97929
> Testcase: igt/kms_pipe_crc_basic/suspend-read-crc-pipe-B
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> Link: http://patchwork.freedesktop.org/patch/msgid/1480955258-26311-1-git-send-email-imre.deak@intel.com
> (cherry picked from commit a0b8a1fe34430c3a82258e8cb45f5968bdf31afd)
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_drv.h      |  2 +
>  drivers/gpu/drm/i915/intel_display.c | 31 +++++----------
>  drivers/gpu/drm/i915/intel_pm.c      | 75 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 87 insertions(+), 21 deletions(-)

What tree is this patch for?  Please give us a hint, we don't like
guessing...

thanks,

greg k-h