[Intel-gfx] [PATCH 3/5] drm/i915: Acquire uncore.lock over intel_uncore_wait_for_register()

[Tvrtko Ursulin]

On 11/04/2017 11:13, Chris Wilson wrote:
> We acquire the forcewake and use I915_READ_FW instead for the atomic
> wait within intel_uncore_wait_for_register. However, this still leaves
> us vulnerable to concurrent mmio access to the register, which can cause
> system hangs on gen7. The protection is to acquire uncore.lock around
> each register, so lets add it back.
>
> v2: Wrap __intel_wait_for_register_fw() to re-use its atomic wait_for
> loop and spare adding another for ourselves.
> v3: Add might_sleep() annotation
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 53c8457869f6..f43121700f83 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1661,14 +1661,22 @@ int intel_wait_for_register(struct drm_i915_private *dev_priv,
>  			    u32 value,
>  			    unsigned int timeout_ms)
>  {
> -
>  	unsigned fw =
>  		intel_uncore_forcewake_for_reg(dev_priv, reg, FW_REG_READ);
>  	int ret;
>
> -	intel_uncore_forcewake_get(dev_priv, fw);
> -	ret = wait_for_us((I915_READ_FW(reg) & mask) == value, 2);
> -	intel_uncore_forcewake_put(dev_priv, fw);
> +	might_sleep();
> +
> +	spin_lock_irq(&dev_priv->uncore.lock);
> +	intel_uncore_forcewake_get__locked(dev_priv, fw);
> +
> +	ret = __intel_wait_for_register_fw(dev_priv,
> +					   reg, mask, value,
> +					   2, 0, NULL);
> +
> +	intel_uncore_forcewake_put__locked(dev_priv, fw);
> +	spin_unlock_irq(&dev_priv->uncore.lock);
> +
>  	if (ret)
>  		ret = wait_for((I915_READ_NOTRACE(reg) & mask) == value,
>  			       timeout_ms);
>

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

Regards,

Tvrtko