[Intel-gfx] [PATCH 2/2] drm/i915: Introduce HAS_2PPC.

[Pandiyan, Dhinakaran]

On Wed, 2017-08-30 at 20:32 +0100, Chris Wilson wrote:
> Quoting Pandiyan, Dhinakaran (2017-08-30 20:12:52)
> > On Wed, 2017-08-16 at 17:54 -0700, Rodrigo Vivi wrote:
> > > Let's make it easier to add platforms that supports 2 pixel per
> > > clock.
> > > 
> > > With spread checks per platform it was easy to miss one or
> > > another spot leading to loose some time on debug.
> > > 
> > > Hopefully this check would save some cases in the future.
> > > 
> > > No functional change.
> > > 
> > > Cc: Paulo Zanoni <paulo.r.zanoni at intel.com>
> > > Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
> > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/i915_drv.h    | 4 ++++
> > >  drivers/gpu/drm/i915/i915_pci.c    | 2 ++
> > >  drivers/gpu/drm/i915/intel_cdclk.c | 8 ++++----
> > >  drivers/gpu/drm/i915/intel_pm.c    | 3 +--
> > >  4 files changed, 11 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > > index 6c25c8520c87..94f5e6522e5e 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.h
> > > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > > @@ -748,6 +748,7 @@ struct intel_csr {
> > >       func(is_lp); \
> > >       func(is_alpha_support); \
> > >       /* Keep has_* in alphabetical order */ \
> > > +     func(has_2ppc); \
> > >       func(has_64bit_reloc); \
> > >       func(has_aliasing_ppgtt); \
> > >       func(has_csr); \
> > > @@ -3025,6 +3026,9 @@ intel_info(const struct drm_i915_private *dev_priv)
> > >  #define NEEDS_WaRsDisableCoarsePowerGating(dev_priv) \
> > >       (IS_SKL_GT3(dev_priv) || IS_SKL_GT4(dev_priv))
> > >  
> > > +/* Supports 2 pixel per clock */
> > > +#define HAS_2PPC(dev_priv) ((dev_priv)->info.has_2ppc)
> > > +
> > 
> > How about
> > #define HAS_2PPC(dev_priv) (IS_GEMINILAKE(dev_priv) ||
> > INTEL_GEN(dev_priv) >= 10) ?
> > 
> > I am not clear on what qualifies for a place in device_info, but
> > defining it this way let's me go to the definition and quickly check
> > which platform has 2 pixels per clock.
> 
> A couple of rules of thumb for starting with:
> 
> Use device_info if:
> 
>  - it fundamentally changes how the device operates, such that knowing
>    about it in debug logs is a key means of triage
>  
>  - number of branches x callsites > 8
>    (some estimate of the cost of inclusion inside device_info vs
>    savings in object code, for a more realistic estimate a branch will
>    ~12 bytes (depending on the phase of the moon) and cost for device
>    info will be the addition of a few strings, and a couple of calls
>    to use those string, so at a guess 100 bytes.)

That's an interesting back-of-the-envelope calculation. I suppose the
compiler is also more likely to load device_info->gen into a register
than device_info->has_2ppc.


> 
> -Chris
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