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

[Jani Nikula <jani.nikula@intel.com>]

On Thu, 24 Nov 2022, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> 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")

So instead just drop the whole intel_de_rewrite_fw() thing and the
locking around the rewrite here?

BR,
Jani.


>
>>  }
>>  
>>  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

-- 
Jani Nikula, Intel Open Source Graphics Center