Re: [Intel-gfx] [PATCH] drm/i915/mst: use intel_de_rmw() to simplify VC payload alloc set/clear

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

On Fri, 13 Aug 2021, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> On Fri, Aug 13, 2021 at 02:56:10PM +0300, Jani Nikula wrote:
>> Less is more, fewer lines to wonder about.
>> 
>> Cc: Manasi Navare <manasi.d.navare@intel.com>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Thanks!

> although sometimes I get myself wondering we might get in some
> case where our check inside the rmw function, to avoid writing the
> same value, could cause some situation where we should perform
> the write operation regardless.

Me too. I could be persuaded to change the rmw function to not optimize
the write away.

BR,
Jani.

>
>> ---
>>  drivers/gpu/drm/i915/display/intel_dp_mst.c | 9 ++-------
>>  1 file changed, 2 insertions(+), 7 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> index 8d13d7b26a25..9859c0334ebc 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
>> @@ -396,7 +396,6 @@ static void intel_mst_post_disable_dp(struct intel_atomic_state *state,
>>  		to_intel_connector(old_conn_state->connector);
>>  	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
>>  	bool last_mst_stream;
>> -	u32 val;
>>  
>>  	intel_dp->active_mst_links--;
>>  	last_mst_stream = intel_dp->active_mst_links == 0;
>> @@ -412,12 +411,8 @@ static void intel_mst_post_disable_dp(struct intel_atomic_state *state,
>>  
>>  	clear_act_sent(encoder, old_crtc_state);
>>  
>> -	val = intel_de_read(dev_priv,
>> -			    TRANS_DDI_FUNC_CTL(old_crtc_state->cpu_transcoder));
>> -	val &= ~TRANS_DDI_DP_VC_PAYLOAD_ALLOC;
>> -	intel_de_write(dev_priv,
>> -		       TRANS_DDI_FUNC_CTL(old_crtc_state->cpu_transcoder),
>> -		       val);
>> +	intel_de_rmw(dev_priv, TRANS_DDI_FUNC_CTL(old_crtc_state->cpu_transcoder),
>> +		     TRANS_DDI_DP_VC_PAYLOAD_ALLOC, 0);
>>  
>>  	wait_for_act_sent(encoder, old_crtc_state);
>>  
>> -- 
>> 2.20.1
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center