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| author | Marta Lofstedt <marta.lofstedt@intel.com> | 2017-09-08 16:28:29 +0300 |
|---|---|---|
| committer | Imre Deak <imre.deak@intel.com> | 2017-09-12 12:19:57 +0300 |
| commit | 3164888a40469c102b5d6d1b756c7646e7eb19e7 (patch) | |
| tree | bcdb1f12d86c2e582b20ff9add6181190922edc7 /drivers/gpu/drm/i915/intel_cdclk.c | |
| parent | d0d5e0d7b11359ccdc7276339ec29d98f4739453 (diff) | |
| download | linux-3164888a40469c102b5d6d1b756c7646e7eb19e7.tar.xz | |
drm/i915: Increase poll time for BDW FCLK_DONE
During IGT testing it has been shown that the specification
defined polling time of 1 us for FCLK_DONE, is sometimes not
enough. The issue is still reproducible while disabling
C-states through the PM QoS framework and also while disabling
preemtion. From this the most plausible explanation is that the
issue is due to a firmware flaw.
As a workaround, it is better to wait a little bit longer for
the FCLK_DONE to come around, than to leave with an DRM_ERROR
and having FCLK_DONE at a randome time after.
While spinning a list of igt tests prone to reproduce the issue
the FCLK_DONE poll failed at approximately 2% of the invocations
of the bdw_set_cdclk function. The longest poll time during this
testing was measured to ~7us. So, the suggested new poll time of
100us is on the safe side.
v2: Added more documentation about investigations done.
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102243
Signed-off-by: Marta Lofstedt <marta.lofstedt@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170908132829.6312-1-marta.lofstedt@intel.com
Diffstat (limited to 'drivers/gpu/drm/i915/intel_cdclk.c')
| -rw-r--r-- | drivers/gpu/drm/i915/intel_cdclk.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c index d32911816fc2..87fc42b19336 100644 --- a/drivers/gpu/drm/i915/intel_cdclk.c +++ b/drivers/gpu/drm/i915/intel_cdclk.c @@ -669,8 +669,12 @@ static void bdw_set_cdclk(struct drm_i915_private *dev_priv, val |= LCPLL_CD_SOURCE_FCLK; I915_WRITE(LCPLL_CTL, val); + /* + * According to the spec, it should be enough to poll for this 1 us. + * However, extensive testing shows that this can take longer. + */ if (wait_for_us(I915_READ(LCPLL_CTL) & - LCPLL_CD_SOURCE_FCLK_DONE, 1)) + LCPLL_CD_SOURCE_FCLK_DONE, 100)) DRM_ERROR("Switching to FCLK failed\n"); val = I915_READ(LCPLL_CTL); |