Re: [PATCH 3/4] drm/i915/hsw: Avoid early timeout during LCPLL disable/restore

Tvrtko Ursulin
2016-06-28T11:17:10Z

On 28/06/16 11:37, Imre Deak wrote:
> Since wait_for_atomic doesn't re-check the wait-for condition after
> expiry of the timeout it can fail when called from non-atomic context
> even if the condition is set correctly before the expiry. Fix this by
> using the non-atomic wait_for instead.
>
> Fixes: 0351b93992aa ("drm/i915: Do not lie about atomic timeout granularity")
> CC: Chris Wilson <chris@chris-wilson.co.uk>
> CC: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
> drivers/gpu/drm/i915/intel_display.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 0312472..d902a70 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -9534,8 +9534,8 @@ static void hsw_disable_lcpll(struct drm_i915_private *dev_priv,
> val |= LCPLL_CD_SOURCE_FCLK;
> I915_WRITE(LCPLL_CTL, val);
>
> - if (wait_for_atomic_us(I915_READ(LCPLL_CTL) &
> - LCPLL_CD_SOURCE_FCLK_DONE, 1))
> + if (wait_for_us(I915_READ(LCPLL_CTL) &
> + LCPLL_CD_SOURCE_FCLK_DONE, 1))
> DRM_ERROR("Switching to FCLK failed\n");
>
> val = I915_READ(LCPLL_CTL);
> @@ -9608,8 +9608,8 @@ static void hsw_restore_lcpll(struct drm_i915_private *dev_priv)
> val &= ~LCPLL_CD_SOURCE_FCLK;
> I915_WRITE(LCPLL_CTL, val);
>
> - if (wait_for_atomic_us((I915_READ(LCPLL_CTL) &
> - LCPLL_CD_SOURCE_FCLK_DONE) == 0, 1))
> + if (wait_for_us((I915_READ(LCPLL_CTL) &
> + LCPLL_CD_SOURCE_FCLK_DONE) == 0, 1))
> DRM_ERROR("Switching back to LCPLL failed\n");
> }
>
>

This one is also on a mutex-taking path so looks correct to me.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Since it just a 1us timeout, as I wrote in another reply I can follow up
with a patch to implement those more efficiently. Does not make anything
worse in the meantime unless operation times out which is not critical.

Regards,

Tvrtko