Re: [PATCH v9 7/7] drm/i915/tgl: Add DC3CO counter in i915_dmc_info

[Imre Deak <imre.deak@intel.com>]

On Fri, Sep 27, 2019 at 10:27:44PM +0530, Anshuman Gupta wrote:
> On 2019-09-27 at 19:38:49 +0300, Imre Deak wrote:
> > On Thu, Sep 26, 2019 at 08:26:21PM +0530, Anshuman Gupta wrote:
> > > Adding DC3CO counter in i915_dmc_info debugfs will be
> > > useful for DC3CO validation.
> > > DMC firmware uses DMC_DEBUG3 register as DC3CO counter
> > > register on TGL, as per B.Specs DMC_DEBUG3 is general
> > > purpose register.
> > > 
> > > Cc: Jani Nikula <jani.nikula@intel.com>
> > > Cc: Imre Deak <imre.deak@intel.com>
> > > Cc: Animesh Manna <animesh.manna@intel.com>
> > > Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/i915_debugfs.c | 6 ++++++
> > >  drivers/gpu/drm/i915/i915_reg.h     | 2 ++
> > >  2 files changed, 8 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> > > index b5b449a88cf1..8a16bbd31212 100644
> > > --- a/drivers/gpu/drm/i915/i915_debugfs.c
> > > +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> > > @@ -2407,6 +2407,12 @@ static int i915_dmc_info(struct seq_file *m, void *unused)
> > >  	seq_printf(m, "version: %d.%d\n", CSR_VERSION_MAJOR(csr->version),
> > >  		   CSR_VERSION_MINOR(csr->version));
> > >  
> > > +	/*
> > > +	 * TGL DMC f/w uses DMC_DEBUG3 register for DC3CO counter.
> > > +	 */
> > 
> > The above is obvious from the code itself, so we don't need a comment
> > for it. Please also consider removing all other comments in the patchset
> > that state only what is obvious from the code.
> DMC_DEBUG3 is a DMC general purpose register, B.Specs doesn't specify
> it as DC3CO counter unlike DC5 and DC6, that is why i have added
> this comment. Shall i remove this comment considering DMC_DEBUG3 
> as general purpose register?

Imo that's an issue in bspec, can you file a ticket there? The comment
could explain what the problem is, the above is already obvious from the
code. Something like:

"NOTE: DMC_DEBUG3 is a general purpose reg, its specification is yet to
be finalized in Bspec for the DC3co counter use."

> > 
> > > +	if (IS_TIGERLAKE(dev_priv))
> > 
> > The above should match the check in get_allowed_dc_mask().
> IS_TIGERLAKE is being checked for the same reason as TGL
> DMC is using DMC_DEBUG3 for DC3CO counter. It may not be true
> for other Gen12 platfrom.

Should we enable then DC3co, if we won't be able to debug it?
In any case DMC_DEBUG3 exists for all GEN12 platforms, so I think we can
safely read it.

> Thanks,
> Anshuman Gupta.  
> > 
> > > +		seq_printf(m, "DC3CO count: %d\n", I915_READ(DMC_DEBUG3));
> > > +
> > >  	if (INTEL_GEN(dev_priv) >= 12) {
> > >  		dc5_reg = TGL_DMC_DEBUG_DC5_COUNT;
> > >  		dc6_reg = TGL_DMC_DEBUG_DC6_COUNT;
> > > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > > index 3ee9720af207..af810f6ed652 100644
> > > --- a/drivers/gpu/drm/i915/i915_reg.h
> > > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > > @@ -7263,6 +7263,8 @@ enum {
> > >  #define TGL_DMC_DEBUG_DC5_COUNT	_MMIO(0x101084)
> > >  #define TGL_DMC_DEBUG_DC6_COUNT	_MMIO(0x101088)
> > >  
> > > +#define DMC_DEBUG3		_MMIO(0x101090)
> > > +
> > >  /* interrupts */
> > >  #define DE_MASTER_IRQ_CONTROL   (1 << 31)
> > >  #define DE_SPRITEB_FLIP_DONE    (1 << 29)
> > > -- 
> > > 2.21.0
> > > 
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