Re: [PATCH] drm/i915: Show debugfs dpcd read failure directly

["Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>]

On Mon, 2018-08-20 at 10:15 +0300, Jani Nikula wrote:
> On Fri, 20 Jul 2018, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> > Instead of using a backchannel if some dpcd read failed we
> > can show that directly on debugfs output.
> > 
> > We are not returning an error because we might still want
> > to know if sub-sequent reads works, but we shouldn't
> > need to check 2 places to see why reg is not on the list.
> 
> Should we just nuke this debugfs and use the aux chardev interface to
> dpcd instead?

Given that this debugfs does not print decoded information, I think, it
offers very little benefit over direct reads. We also print some DPCD's
in dmesg, so I'm in favour of killing it. Don't see the file being used
in IGTs either.

Your comment also reminds about the IGT tool that Tarun started writing
for reading DPCD.

-DK


> 
> BR,
> Jani.
> 
> > 
> > Cc: Jani Nikula <jani.nikula@intel.com>
> > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_debugfs.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c
> > b/drivers/gpu/drm/i915/i915_debugfs.c
> > index 59dc0610ea44..5d8da4e8c444 100644
> > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > @@ -4846,8 +4846,8 @@ static int i915_dpcd_show(struct seq_file *m,
> > void *data)
> >  
> >  		err = drm_dp_dpcd_read(&intel_dp->aux, b->offset,
> > buf, size);
> >  		if (err <= 0) {
> > -			DRM_ERROR("dpcd read (%zu bytes at %u)
> > failed (%zd)\n",
> > -				  size, b->offset, err);
> > +			seq_printf(m, "dpcd read (%zu bytes at %u)
> > failed (%zd)\n",
> > +				   size, b->offset, err);
> >  			continue;
> >  		}
> 
> 
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