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

[Imre Deak <imre.deak@intel.com>]

On Thu, 2017-01-12 at 18:21 +0100, Greg Kroah-Hartman wrote:
> On Thu, Jan 12, 2017 at 03:22:38PM +0200, Imre Deak wrote:
> > commit 848496e5902833600f7992f4faa82dc1546051ba
> > Author: Ville Syrjälä <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 Syrjälä <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...

It's for the 4.9 stable tree and for other stable trees starting from 4.2.
It's the upstream commit a0b8a1fe34430c3a82258e8cb45f5968bdf31afd
rebased on top of 4.9.2 according to our discussion at
http://www.spinics.net/lists/stable/msg155406.html

--Imre