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 14:15:30 +0200	[thread overview]
Message-ID: <87pnf9gie5.fsf@intel.com> (raw)
In-Reply-To: <20200124115951.GC24118@intel.com>

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.

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
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