[PATCH] drm/i915/dp: Improve clock recovery loop limit comment

[PATCH] drm/i915/dp: Improve clock recovery loop limit comment

[Nathan Ciobanu]

Clarifies the clock recovery loop limit comment that 80
max_cr_tries for pre-DP1.4 devices was chosen as a very
tolerant upper bound.
Assumptions made:
- DP1.4 syncs should be smarter so they won't need more
than 10 tries
- pre-DP1.4 syncs should be compliant enough to not need
that many tries (80) but we should tolerate any that may
trigger this corner case

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Marc Herbert <marc.herbert@intel.com>
Suggested-by: Marc Herbert <marc.herbert@intel.com>
Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 07e128c7443c..a9f40985a621 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -172,10 +172,12 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 	}
 
 	/*
-	 * DP 1.4 spec clock recovery retries defined but
-	 * for devices pre-DP 1.4 we set the retry limit
-	 * to 4 (voltage levels) x 4 (preemphasis levels) x
-	 * x 5 (same voltage retries) = 80 (max iterations)
+	 * The DP 1.4 spec defines the max clock recovery retries value
+	 * as 10 but for pre-DP 1.4 devices we set a very tolerant
+	 * retry limit of 80 (4 voltage levels x 4 preemphasis levels x
+	 * x 5 identical voltage retries). Since the previous specs didn't
+	 * define a limit and created the possibility of an infinite loop
+	 * we want to prevent any sync from triggering that corner case.
 	 */
 	if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
 		max_cr_tries = 10;
-- 
1.9.1

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✓ Fi.CI.BAT: success for drm/i915/dp: Improve clock recovery loop limit comment

[Patchwork]

== Series Details ==

Series: drm/i915/dp: Improve clock recovery loop limit comment
URL   : https://patchwork.freedesktop.org/series/47156/
State : success

== Summary ==

= CI Bug Log - changes from CI_DRM_4537 -> Patchwork_9759 =

== Summary - SUCCESS ==

  No regressions found.

  External URL: https://patchwork.freedesktop.org/api/1.0/series/47156/revisions/1/mbox/

== Known issues ==

  Here are the changes found in Patchwork_9759 that come from known issues:

  === IGT changes ===

    ==== Issues hit ====

    igt@drv_selftest@live_hangcheck:
      fi-kbl-7560u:       PASS -> DMESG-FAIL (fdo#106947, fdo#106560)

    igt@drv_selftest@live_workarounds:
      fi-cfl-8700k:       PASS -> DMESG-FAIL (fdo#107292)
      {fi-bsw-kefka}:     PASS -> DMESG-FAIL (fdo#107292)

    igt@kms_flip@basic-flip-vs-modeset:
      fi-glk-j4005:       PASS -> DMESG-WARN (fdo#106097, fdo#106000)

    igt@kms_flip@basic-flip-vs-wf_vblank:
      fi-glk-j4005:       PASS -> FAIL (fdo#100368)

    
    ==== Possible fixes ====

    igt@drv_selftest@live_hangcheck:
      fi-bdw-5557u:       DMESG-FAIL (fdo#106560) -> PASS

    
  {name}: This element is suppressed. This means it is ignored when computing
          the status of the difference (SUCCESS, WARNING, or FAILURE).

  fdo#100368 https://bugs.freedesktop.org/show_bug.cgi?id=100368
  fdo#106000 https://bugs.freedesktop.org/show_bug.cgi?id=106000
  fdo#106097 https://bugs.freedesktop.org/show_bug.cgi?id=106097
  fdo#106560 https://bugs.freedesktop.org/show_bug.cgi?id=106560
  fdo#106947 https://bugs.freedesktop.org/show_bug.cgi?id=106947
  fdo#107292 https://bugs.freedesktop.org/show_bug.cgi?id=107292


== Participating hosts (49 -> 41) ==

  Missing    (8): fi-ilk-m540 fi-hsw-4200u fi-byt-squawks fi-bsw-cyan fi-ctg-p8600 fi-skl-caroline fi-byt-clapper fi-bdw-samus 


== Build changes ==

    * Linux: CI_DRM_4537 -> Patchwork_9759

  CI_DRM_4537: d14ba41a37d886280f69ba42c82c34654de09efc @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_4573: 2884f91dd6d7682ea738ef6f0943cc591643dda2 @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_9759: 10a56f828a6f36adff10fe51812cc27c5a49e85d @ git://anongit.freedesktop.org/gfx-ci/linux


== Linux commits ==

10a56f828a6f drm/i915/dp: Improve clock recovery loop limit comment

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_9759/issues.html
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Re: [PATCH] drm/i915/dp: Improve clock recovery loop limit comment

[Marc Herbert]

Reviewed-by: Marc Herbert <marc.herbert@intel.com>

Thx Nathan, I think this helps. I'm still curious how training normally
converges much faster than the total number of possibilities but - unlike
this latest clarification below - I expect the spec(s) to document that.


On 24/07/2018 15:33, Nathan Ciobanu wrote:
> Clarifies the clock recovery loop limit comment that 80
> max_cr_tries for pre-DP1.4 devices was chosen as a very
> tolerant upper bound.
> Assumptions made:
> - DP1.4 syncs should be smarter so they won't need more
> than 10 tries
> - pre-DP1.4 syncs should be compliant enough to not need
> that many tries (80) but we should tolerate any that may
> trigger this corner case
> 
> Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Marc Herbert <marc.herbert@intel.com>
> Suggested-by: Marc Herbert <marc.herbert@intel.com>
> Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>
> 
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 07e128c7443c..a9f40985a621 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -172,10 +172,12 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
>  	}
>  
>  	/*
> -	 * DP 1.4 spec clock recovery retries defined but
> -	 * for devices pre-DP 1.4 we set the retry limit
> -	 * to 4 (voltage levels) x 4 (preemphasis levels) x
> -	 * x 5 (same voltage retries) = 80 (max iterations)
> +	 * The DP 1.4 spec defines the max clock recovery retries value
> +	 * as 10 but for pre-DP 1.4 devices we set a very tolerant
> +	 * retry limit of 80 (4 voltage levels x 4 preemphasis levels x
> +	 * x 5 identical voltage retries). Since the previous specs didn't
> +	 * define a limit and created the possibility of an infinite loop
> +	 * we want to prevent any sync from triggering that corner case.
>  	 */
>  	if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
>  		max_cr_tries = 10;
> 

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✗ Fi.CI.IGT: failure for drm/i915/dp: Improve clock recovery loop limit comment

[Patchwork]

== Series Details ==

Series: drm/i915/dp: Improve clock recovery loop limit comment
URL   : https://patchwork.freedesktop.org/series/47156/
State : failure

== Summary ==

= CI Bug Log - changes from CI_DRM_4537_full -> Patchwork_9759_full =

== Summary - FAILURE ==

  Serious unknown changes coming with Patchwork_9759_full absolutely need to be
  verified manually.
  
  If you think the reported changes have nothing to do with the changes
  introduced in Patchwork_9759_full, please notify your bug team to allow them
  to document this new failure mode, which will reduce false positives in CI.

  

== Possible new issues ==

  Here are the unknown changes that may have been introduced in Patchwork_9759_full:

  === IGT changes ===

    ==== Possible regressions ====

    igt@drv_module_reload@basic-reload:
      shard-glk:          PASS -> DMESG-WARN

    
    ==== Warnings ====

    igt@pm_rc6_residency@rc6-accuracy:
      shard-kbl:          SKIP -> PASS +1

    
== Known issues ==

  Here are the changes found in Patchwork_9759_full that come from known issues:

  === IGT changes ===

    ==== Issues hit ====

    igt@kms_flip@flip-vs-expired-vblank:
      shard-glk:          PASS -> FAIL (fdo#102887, fdo#105363)

    igt@kms_flip@plain-flip-ts-check:
      shard-glk:          PASS -> FAIL (fdo#100368)

    
    ==== Possible fixes ====

    igt@gem_exec_await@wide-contexts:
      shard-glk:          FAIL (fdo#105900) -> PASS

    igt@kms_cursor_crc@cursor-256x256-suspend:
      shard-hsw:          INCOMPLETE (fdo#103540) -> PASS

    igt@kms_flip@2x-flip-vs-expired-vblank:
      shard-glk:          FAIL (fdo#105363) -> PASS

    igt@kms_flip@2x-flip-vs-expired-vblank-interruptible:
      shard-glk:          FAIL (fdo#105189) -> PASS

    igt@kms_flip@dpms-vs-vblank-race:
      shard-snb:          FAIL (fdo#103060) -> PASS

    
  fdo#100368 https://bugs.freedesktop.org/show_bug.cgi?id=100368
  fdo#102887 https://bugs.freedesktop.org/show_bug.cgi?id=102887
  fdo#103060 https://bugs.freedesktop.org/show_bug.cgi?id=103060
  fdo#103540 https://bugs.freedesktop.org/show_bug.cgi?id=103540
  fdo#105189 https://bugs.freedesktop.org/show_bug.cgi?id=105189
  fdo#105363 https://bugs.freedesktop.org/show_bug.cgi?id=105363
  fdo#105900 https://bugs.freedesktop.org/show_bug.cgi?id=105900


== Participating hosts (5 -> 5) ==

  No changes in participating hosts


== Build changes ==

    * Linux: CI_DRM_4537 -> Patchwork_9759

  CI_DRM_4537: d14ba41a37d886280f69ba42c82c34654de09efc @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_4573: 2884f91dd6d7682ea738ef6f0943cc591643dda2 @ git://anongit.freedesktop.org/xorg/app/intel-gpu-tools
  Patchwork_9759: 10a56f828a6f36adff10fe51812cc27c5a49e85d @ git://anongit.freedesktop.org/gfx-ci/linux
  piglit_4509: fdc5a4ca11124ab8413c7988896eec4c97336694 @ git://anongit.freedesktop.org/piglit

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_9759/shards.html
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Re: [PATCH] drm/i915/dp: Improve clock recovery loop limit comment

[Rodrigo Vivi]

On Tue, Jul 24, 2018 at 05:17:53PM -0700, Marc Herbert wrote:
> Reviewed-by: Marc Herbert <marc.herbert@intel.com>

pushed, thanks.

> 
> Thx Nathan, I think this helps. I'm still curious how training normally
> converges much faster than the total number of possibilities but - unlike
> this latest clarification below - I expect the spec(s) to document that.
> 
> 
> On 24/07/2018 15:33, Nathan Ciobanu wrote:
> > Clarifies the clock recovery loop limit comment that 80
> > max_cr_tries for pre-DP1.4 devices was chosen as a very
> > tolerant upper bound.
> > Assumptions made:
> > - DP1.4 syncs should be smarter so they won't need more
> > than 10 tries
> > - pre-DP1.4 syncs should be compliant enough to not need
> > that many tries (80) but we should tolerate any that may
> > trigger this corner case
> > 
> > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Cc: Marc Herbert <marc.herbert@intel.com>
> > Suggested-by: Marc Herbert <marc.herbert@intel.com>
> > Signed-off-by: Nathan Ciobanu <nathan.d.ciobanu@linux.intel.com>
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > index 07e128c7443c..a9f40985a621 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > @@ -172,10 +172,12 @@ static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
> >  	}
> >  
> >  	/*
> > -	 * DP 1.4 spec clock recovery retries defined but
> > -	 * for devices pre-DP 1.4 we set the retry limit
> > -	 * to 4 (voltage levels) x 4 (preemphasis levels) x
> > -	 * x 5 (same voltage retries) = 80 (max iterations)
> > +	 * The DP 1.4 spec defines the max clock recovery retries value
> > +	 * as 10 but for pre-DP 1.4 devices we set a very tolerant
> > +	 * retry limit of 80 (4 voltage levels x 4 preemphasis levels x
> > +	 * x 5 identical voltage retries). Since the previous specs didn't
> > +	 * define a limit and created the possibility of an infinite loop
> > +	 * we want to prevent any sync from triggering that corner case.
> >  	 */
> >  	if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
> >  		max_cr_tries = 10;
> > 
> 
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> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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