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

[Chris Wilson]

On Tue, Jun 28, 2016 at 01:37:30PM +0300, 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.

wait_for_atomic is indeed only safe to be called from atomic context.
Likewise, wait_for is only safe to called from !atomic context.

> 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")

The bug would be using wait_for_atomic from non-atomic context, and so
older.


> CC: Chris Wilson <chris at chris-wilson.co.uk>
> CC: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Signed-off-by: Imre Deak <imre.deak at 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))

Does this work with CONFIG_I915_DEBUG and CONFIG_DEBUG_ATOMIC_SLEEP ?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre