[Intel-gfx] [PATCH v1 1/1] drm/i915: Skip applying copy engine fuses

[Andi Shyti]

Hi Lucas,

On Mon, Sep 12, 2022 at 11:12:47AM -0700, Lucas De Marchi wrote:
> On Mon, Sep 12, 2022 at 06:59:53PM +0200, Andi Shyti wrote:
> > Hi Lucas,
> > 
> > On Mon, Sep 12, 2022 at 09:19:38AM -0700, Lucas De Marchi wrote:
> > > Support for reading the fuses to check what are the Link Copy engines
> > > was added in commit ad5f74f34201 ("drm/i915/pvc: read fuses for link
> > > copy engines"). However they were added unconditionally because the
> > > FUSE3 register is present since graphics version 10.
> > > 
> > > However the bitfield with meml3 fuses only exists since graphics version
> > > 12. Moreover, Link Copy engines are currently only available in PVC.
> > > Tying additional copy engines to the meml3 fuses is not correct for
> > > other platforms.
> > > 
> > > Make sure there is a check for  `12.60 <= ver < 12.70`. Later platforms
> > > may extend this function later if it's needed to fuse off copy engines.
> > > 
> > > Currently it's harmless as the Link Copy engines are still not exported:
> > > info->engine_mask only has BCS0 set and the register is only read for
> > > platforms that do have it.
> > > 
> > > Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
> > > 
> > > diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > > index 814f83b5fe59..1f7188129cd1 100644
> > > --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > > +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> > > @@ -764,6 +764,10 @@ static void engine_mask_apply_copy_fuses(struct intel_gt *gt)
> > >  	unsigned long meml3_mask;
> > >  	unsigned long quad;
> > > 
> > > +	if (!(GRAPHICS_VER_FULL(i915) >= IP_VER(12, 60) &&
> > > +	      GRAPHICS_VER_FULL(i915) < IP_VER(12, 70)))
> > > +		return;
> > > +
> > 
> > Isn't it easier if you wrote
> > 
> > 	if (GRAPHICS_VER_FULL(i915) < IP_VER(12, 60) ||
> > 	    GRAPHICS_VER_FULL(i915) >= IP_VER(12, 70))
> > 		return;
> > 
> > ?
> > 
> > You save a parenthesis and a negation '!'.
> 
> but that makes it wrong. I'd really want the range
> 12.60 <= version < 12.70, so it applies to PVC  but is then disabled
> again for MTL.

But it's negated... so that if it's not in the range, it's
outside of the range... right?

 NOT(12.60 <= ver < 12.70)   <--- you wrote

is the same as:

 ver < 12.60 or ver >= 12.70 <--- I suggested

and it would mean (just to see if I'm not getting confused by
something and the negations do always confuse me):


                 12.60          12.70
        return     |              |     return
  ver: ------------[--------------[---------------


But it's the same, taht's why I r-b it anyway.

> Depending on how this evolves for future platforms, we
> may change it to a feature flag or just check by platform
> name. For now I think this is the most future-proof option.

yes, I got the point and I think it's fine.

Andi

> Lucas De Marchi
> 
> > 
> > Anyway, looks good:
> > 
> > Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>
> > 
> > Andi
> > 
> > >  	meml3_mask = intel_uncore_read(gt->uncore, GEN10_MIRROR_FUSE3);
> > >  	meml3_mask = REG_FIELD_GET(GEN12_MEML3_EN_MASK, meml3_mask);
> > > 
> > > 
> > > --
> > > b4 0.10.0-dev-df873