Re: [PATCH 1/4] drm/i915/bxt: Avoid early timeout during PLL enable

Tvrtko Ursulin
2016-06-28T11:27:03Z

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.
>
> I noticed this via the PLL locking timing out incorrectly, with this fix
> I couldn't reproduce the problem.
>
> 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_dpll_mgr.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> index c0eff15..e130c3e 100644
> --- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
> +++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
> @@ -1374,8 +1374,8 @@ static void bxt_ddi_pll_enable(struct drm_i915_private *dev_priv,
> I915_WRITE(BXT_PORT_PLL_ENABLE(port), temp);
> POSTING_READ(BXT_PORT_PLL_ENABLE(port));
>
> - if (wait_for_atomic_us((I915_READ(BXT_PORT_PLL_ENABLE(port)) &
> - PORT_PLL_LOCK), 200))
> + if (wait_for_us((I915_READ(BXT_PORT_PLL_ENABLE(port)) & PORT_PLL_LOCK),
> + 200))
> DRM_ERROR("PLL %d not locked\n", port);
>
> /*
>

This one was a bit more work to verify but is definitely a non-atomic
path as well.

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

Regards,

Tvrtko