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

[Michal Wajdeczko]

On Mon, Apr 10, 2017 at 04:02:07PM +0100, 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.
> 
> 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 | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 53c8457869f6..d2ba3011c2f0 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1661,14 +1661,18 @@ 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);
> +	spin_lock_irq(&dev_priv->uncore.lock);
> +	intel_uncore_forcewake_get__locked(dev_priv, fw);
> +
>  	ret = wait_for_us((I915_READ_FW(reg) & mask) == value, 2);

To further decrease driver size we may try to call here our helper function:

	ret = __intel_wait_for_register_fw(dev_priv, reg, mask, value, 2, 0, NULL);

-Michal

> -	intel_uncore_forcewake_put(dev_priv, fw);
> +
> +	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);
> -- 
> 2.11.0
>