Re: [Intel-gfx] [PATCH 1/2] drm/i915/dp: Define each HBR link rate

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Dec 03, 2019 at 11:08:52AM +0200, Jani Nikula wrote:
> On Mon, 02 Dec 2019, José Roberto de Souza <jose.souza@intel.com> wrote:
> > This is better than keep those values in the code that you always
> > need to check the DP spec to know what level of HBR it is.
> >
> > Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_ddi.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> > index a976606d21c7..914f0cc4d237 100644
> > --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> > @@ -49,6 +49,10 @@
> >  #include "intel_tc.h"
> >  #include "intel_vdsc.h"
> >  
> > +#define HBR_RATE 270000
> > +#define HBR2_RATE 540000
> > +#define HBR3_RATE 810000
> > +
> >  struct ddi_buf_trans {
> >  	u32 trans1;	/* balance leg enable, de-emph level */
> >  	u32 trans2;	/* vref sel, vswing */
> > @@ -888,7 +892,7 @@ icl_get_combo_buf_trans(struct drm_i915_private *dev_priv, int type, int rate,
> >  	if (type == INTEL_OUTPUT_HDMI) {
> >  		*n_entries = ARRAY_SIZE(icl_combo_phy_ddi_translations_hdmi);
> >  		return icl_combo_phy_ddi_translations_hdmi;
> > -	} else if (rate > 540000 && type == INTEL_OUTPUT_EDP) {
> > +	} else if (rate > HBR2_RATE && type == INTEL_OUTPUT_EDP) {
> 
> I don't want a patch switching some random place to using a
> macro. Either we stick to numbers or switch all.
> 
> And if switch all, add the rates to drm core, not locally to
> intel_ddi.c. (And then wonder what to do with the intermediate rates in
> intel_dp_set_source_rates()...)

Yeah, we'll still end up with a mix of defines and raw numbers.

> 
> Personally, HBR<N> is less useful to me in code, it's the actual rate
> that helps me.
> 
> But I'll trust Ville's judgement on this one.

I tend to prefer raw numbers for this sort of stuff. If we didn't have
the intermediate rates I might have a different opinion. The only thing
I really worry about with raw numbers is the potential for typos.

The original problem of bspec talking about hbr2 in the bug trans
tables we could probably solve with a comment.

-- 
Ville Syrjälä
Intel
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