• Imre Deak's avatar
    drm/i915/gen9: Fix PCODE polling during CDCLK change notification · a0b8a1fe
    Imre Deak authored
    commit 848496e5
    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)
    
    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- : 3b2c1710 : drm/i915: Wait up to 3ms
    Cc: <stable@vger.kernel.org> # v4.2-
    Fixes: 5d96d8af ("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: default avatarImre Deak <imre.deak@intel.com>
    Reviewed-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Link: http://patchwork.freedesktop.org/patch/msgid/1480955258-26311-1-git-send-email-imre.deak@intel.com
    a0b8a1fe
intel_display.c 487 KB