Re: [Intel-gfx] [RFC 1/6] drm/i915: Iterate over pipe and skip the disabled one

From: Jani Nikula <jani.nikula@intel.com>
To: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [RFC 1/6] drm/i915: Iterate over pipe and skip the disabled one
Date: Fri, 24 Jan 2020 15:34:52 +0200	[thread overview]
Message-ID: <87k15hgepv.fsf@intel.com> (raw)
In-Reply-To: <20200124121931.GD24118@intel.com>

On Fri, 24 Jan 2020, Anshuman Gupta <anshuman.gupta@intel.com> wrote:
> On 2020-01-24 at 14:15:30 +0200, Jani Nikula wrote:
>> On Fri, 24 Jan 2020, Anshuman Gupta <anshuman.gupta@intel.com> wrote:
>> > On 2020-01-23 at 15:48:05 +0200, Jani Nikula wrote:
>> >> On Thu, 23 Jan 2020, Anshuman Gupta <anshuman.gupta@intel.com> wrote:
>> >> > It should not be assumed that a disabled display pipe will be
>> >> > always last the pipe.
>> >> > for_each_pipe() should iterate over I915_MAX_PIPES and check
>> >> > for the disabled pipe and skip that pipe so that it should not
>> >> > initialize the intel crtc for any disabled pipes.
>> >> >
>> >> > Few compilation error needed to handle accordingly due to
>> >> > change in for_each_pipe() macro.
>> >> 
>> >> Really? Please paste.
>> > It is dangling-else warning at couple of places.
>> > drivers/gpu/drm/i915/i915_irq.c:1861:5: error: suggest explicit braces to avoid ambiguous ‘else’ [-Werror=dangling-else]
>> >  1861 |  if (pch_iir & SDE_FDI_MASK)
>> > drivers/gpu/drm/i915/i915_irq.c:1944:5: error: suggest explicit braces to avoid ambiguous ‘else’ [-Werror=dangling-else]
>> > 1944 |  if (pch_iir & SDE_FDI_MASK_CPT)
>> 
>> Right, I suppose this is caused by the nesting of the for loops with
>> if-else.
>> 
>> Perhaps the right course of action is to *not* reuse for_each_pipe() in
>> for_each_pipe_masked(). Just combine the conditions into one.
> This is not caused by for_each_pipe_masked, this is caused by for_each_pipe itself,
> if (foo)
> 	/*for_each_pipe()*/
> 	for(;;)
> 		if (condition) {}
> 		else

Sorry for the noise, please carry on with the patch.

*blush*

BR,
Jani.

>> 
>> BR,
>> Jani.
>> 
>> 
>> 
>> >> 
>> >> >
>> >> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> >> > Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
>> >> > ---
>> >> >  drivers/gpu/drm/i915/display/intel_display.h | 5 +++--
>> >> >  drivers/gpu/drm/i915/i915_irq.c              | 6 ++++--
>> >> >  2 files changed, 7 insertions(+), 4 deletions(-)
>> >> >
>> >> > diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
>> >> > index 028aab728514..47813a50add4 100644
>> >> > --- a/drivers/gpu/drm/i915/display/intel_display.h
>> >> > +++ b/drivers/gpu/drm/i915/display/intel_display.h
>> >> > @@ -312,10 +312,11 @@ enum phy_fia {
>> >> >  };
>> >> >  
>> >> >  #define for_each_pipe(__dev_priv, __p) \
>> >> > -	for ((__p) = 0; (__p) < INTEL_NUM_PIPES(__dev_priv); (__p)++)
>> >> > +	for ((__p) = 0; (__p) < I915_MAX_PIPES; (__p)++) \
>> >> 
>> >> Originally I was envisioning using for_each_set_bit() from bitops.h for
>> >> this. It's probably more efficient, however I'm not sure if efficiency
>> >> matters much here. The ugly part is that for_each_set_bit() requires an
>> >> explicit cast to unsigned long *.
>> >> 
>> >> Perhaps this is just as well, it's not wrong, and can always be updated
>> >> later.
>> >> 
>> >> > +		for_each_if((INTEL_INFO(__dev_priv)->pipe_mask) & BIT(__p))
>> >> >  
>> >> >  #define for_each_pipe_masked(__dev_priv, __p, __mask) \
>> >> > -	for ((__p) = 0; (__p) < INTEL_NUM_PIPES(__dev_priv); (__p)++) \
>> >> > +	for_each_pipe(__dev_priv, __p) \
>> >> >  		for_each_if((__mask) & BIT(__p))
>> >> >  
>> >> >  #define for_each_cpu_transcoder_masked(__dev_priv, __t, __mask) \
>> >> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
>> >> > index 94cb25ac504d..22ecd5bc407e 100644
>> >> > --- a/drivers/gpu/drm/i915/i915_irq.c
>> >> > +++ b/drivers/gpu/drm/i915/i915_irq.c
>> >> > @@ -1735,11 +1735,12 @@ static void ibx_irq_handler(struct drm_i915_private *dev_priv, u32 pch_iir)
>> >> >  	if (pch_iir & SDE_POISON)
>> >> >  		DRM_ERROR("PCH poison interrupt\n");
>> >> >  
>> >> > -	if (pch_iir & SDE_FDI_MASK)
>> >> > +	if (pch_iir & SDE_FDI_MASK) {
>> >> >  		for_each_pipe(dev_priv, pipe)
>> >> >  			DRM_DEBUG_DRIVER("  pipe %c FDI IIR: 0x%08x\n",
>> >> >  					 pipe_name(pipe),
>> >> >  					 I915_READ(FDI_RX_IIR(pipe)));
>> >> > +	}
>> >> 
>> >> Are the brace changes really needed? This is what the for_each_if hack
>> >> is supposed to tackle.
>> > IMHO it was dangling-else compilation, warning that requires braces.
>> > please correct me if i am wrong.
>> > Thanks,
>> > Anshuman
>> >> 
>> >> >  
>> >> >  	if (pch_iir & (SDE_TRANSB_CRC_DONE | SDE_TRANSA_CRC_DONE))
>> >> >  		DRM_DEBUG_DRIVER("PCH transcoder CRC done interrupt\n");
>> >> > @@ -1818,11 +1819,12 @@ static void cpt_irq_handler(struct drm_i915_private *dev_priv, u32 pch_iir)
>> >> >  	if (pch_iir & SDE_AUDIO_CP_CHG_CPT)
>> >> >  		DRM_DEBUG_DRIVER("Audio CP change interrupt\n");
>> >> >  
>> >> > -	if (pch_iir & SDE_FDI_MASK_CPT)
>> >> > +	if (pch_iir & SDE_FDI_MASK_CPT) {
>> >> >  		for_each_pipe(dev_priv, pipe)
>> >> >  			DRM_DEBUG_DRIVER("  pipe %c FDI IIR: 0x%08x\n",
>> >> >  					 pipe_name(pipe),
>> >> >  					 I915_READ(FDI_RX_IIR(pipe)));
>> >> > +	}
>> >> >  
>> >> >  	if (pch_iir & SDE_ERROR_CPT)
>> >> >  		cpt_serr_int_handler(dev_priv);
>> >> 
>> >> -- 
>> >> Jani Nikula, Intel Open Source Graphics Center
>> 
>> -- 
>> Jani Nikula, Intel Open Source Graphics Center

-- 
Jani Nikula, Intel Open Source Graphics Center
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