Re: [PATCH] drm/i915: Check for fused or unused pipes

From: Dhinakaran Pandiyan <dhinakaran.pandiyan@gmail.com>
To: Jani Nikula <jani.nikula@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Check for fused or unused pipes
Date: Fri, 15 Dec 2017 02:11:14 -0800	[thread overview]
Message-ID: <1567972.C5yPD2RT9q@dk> (raw)
In-Reply-To: <87vah8pcih.fsf@intel.com>

On Friday, December 15, 2017 11:27:02 AM PST Jani Nikula wrote:
> On Fri, 15 Dec 2017, Dhinakaran Pandiyan <dhinakaran.pandiyan@gmail.com> 
wrote:
> > On Friday, December 15, 2017 9:59:02 AM PST Mika Kahola wrote:
> >> In case of fused or unused pipes, return early with a warning when
> >> reading
> >> information for encoder.
> >> 
> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103206
> >> Reported-by: Thomas Gleixner <tglx@linutronix.de>
> >> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >> Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> >> ---
> >> 
> >>  drivers/gpu/drm/i915/intel_audio.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/gpu/drm/i915/intel_audio.c
> >> b/drivers/gpu/drm/i915/intel_audio.c index f1502a0..522d54f 100644
> >> --- a/drivers/gpu/drm/i915/intel_audio.c
> >> +++ b/drivers/gpu/drm/i915/intel_audio.c
> >> @@ -779,7 +779,7 @@ static struct intel_encoder *get_saved_enc(struct
> >> drm_i915_private *dev_priv, {
> >> 
> >>  	struct intel_encoder *encoder;
> >> 
> >> -	if (WARN_ON(pipe >= INTEL_INFO(dev_priv)->num_pipes))
> >> +	if (WARN_ON(pipe >= ARRAY_SIZE(dev_priv->av_enc_map)))
> >> 
> >>  		return NULL;
> > 
> > I think we should remove the WARN_ON() and just return NULL. The error
> > return and the debug message we print in the caller is good enough IMO.
> 
> On the contrary, I think this one is fine with WARN_ON. The commit
> message is inaccurate. This will only become a bounds check with the
> change, and I think it's important to catch the totally out of bounds
> values loudly.
> 

My concern was that we don't expose any interface to tell the audio driver how 
many pipes are present, so a WARN_ON would be unreasonable. But on second 
thoughts, audio should have ways to find that information from the hardware.

> In case of fused or unused pipes, the code will happily pass that check,
> and check the av_enc_map for whether the pipe is available or not.
> 
> BR,
> Jani.
> 
> >>  	/* MST */

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