Re: [Intel-gfx] [PATCH 12/12] drm/i915/fbc: switch to intel_de_* register accessors in display code

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Nov 23, 2022 at 11:18:25PM +0200, Jani Nikula wrote:
> Avoid direct uncore use in display code. Use the new
> intel_de_rewrite_fw().
> 
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fbc.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index b5ee5ea0d010..6066ac412e6f 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> @@ -323,10 +323,7 @@ static void i8xx_fbc_nuke(struct intel_fbc *fbc)
>  	enum i9xx_plane_id i9xx_plane = fbc_state->plane->i9xx_plane;
>  	struct drm_i915_private *dev_priv = fbc->i915;
>  
> -	spin_lock_irq(&dev_priv->uncore.lock);
> -	intel_de_write_fw(dev_priv, DSPADDR(i9xx_plane),
> -			  intel_de_read_fw(dev_priv, DSPADDR(i9xx_plane)));
> -	spin_unlock_irq(&dev_priv->uncore.lock);
> +	intel_de_rewrite_fw(dev_priv, DSPADDR(i9xx_plane));

intel_de_rewrite_fw() seems to imply some kind of atomicicity guarantee
here. But that entirely depends on whether the other writers of this
register also protect it with unore.lock. So just a misleading illusion.

That said, this locking stuff shouldn't even be needed since 
commit de5bd083d247 ("drm/i915/fbc: Skip nuke when flip is pending")
commit 7cfd1a18c5f9 ("drm/i915: Remove remaining locks from i9xx plane udpates")

>  }
>  
>  static void i8xx_fbc_program_cfb(struct intel_fbc *fbc)
> @@ -359,10 +356,7 @@ static void i965_fbc_nuke(struct intel_fbc *fbc)
>  	enum i9xx_plane_id i9xx_plane = fbc_state->plane->i9xx_plane;
>  	struct drm_i915_private *dev_priv = fbc->i915;
>  
> -	spin_lock_irq(&dev_priv->uncore.lock);
> -	intel_de_write_fw(dev_priv, DSPSURF(i9xx_plane),
> -			  intel_de_read_fw(dev_priv, DSPSURF(i9xx_plane)));
> -	spin_unlock_irq(&dev_priv->uncore.lock);
> +	intel_de_rewrite_fw(dev_priv, DSPSURF(i9xx_plane));
>  }
>  
>  static const struct intel_fbc_funcs i965_fbc_funcs = {
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel