[Intel-gfx] [PATCH v2 06/19] drm/i915/dsb: Avoid corrupting the first register write

[Manna, Animesh]

> -----Original Message-----
> From: Manna, Animesh
> Sent: Wednesday, July 5, 2023 3:10 PM
> To: Ville Syrjala <ville.syrjala at linux.intel.com>; intel-
> gfx at lists.freedesktop.org
> Subject: RE: [Intel-gfx] [PATCH v2 06/19] drm/i915/dsb: Avoid corrupting the
> first register write
> 
> 
> 
> > -----Original Message-----
> > From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of
> > Ville Syrjala
> > Sent: Wednesday, June 7, 2023 12:45 AM
> > To: intel-gfx at lists.freedesktop.org
> > Subject: [Intel-gfx] [PATCH v2 06/19] drm/i915/dsb: Avoid corrupting
> > the first register write
> >
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >
> > i915_gem_object_create_internal() does not hand out zeroed memory.
> > Thus we may confuse whatever stale garbage is in there as a previous
> > register write and mistakenly handle the first actual register write
> > as an indexed write. This can end up corrupting the instruction
> > sufficiently well to lose the entire register write.
> >
> > Make sure we've actually emitted a previous instruction before
> > attemting indexed register write merging.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> LGTM.
> Signed-off-by: Animesh Manna <animesh.manna at intel.com>

Correction! By mistake added my Signed-off-by.

Reviewed-by: Animesh Manna <animesh.manna at intel.com>

> 
> > ---
> >  drivers/gpu/drm/i915/display/intel_dsb.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
> > b/drivers/gpu/drm/i915/display/intel_dsb.c
> > index 093b2567883d..a20ae5313d23 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> > @@ -141,6 +141,14 @@ static bool intel_dsb_prev_ins_is_write(struct
> > intel_dsb *dsb,
> >  	const u32 *buf = dsb->cmd_buf;
> >  	u32 prev_opcode, prev_reg;
> >
> > +	/*
> > +	 * Nothing emitted yet? Must check before looking
> > +	 * at the actual data since i915_gem_object_create_internal()
> > +	 * does *not* give you zeroed memory!
> > +	 */
> > +	if (dsb->free_pos == 0)
> > +		return false;
> > +
> >  	prev_opcode = buf[dsb->ins_start_offset + 1] >>
> DSB_OPCODE_SHIFT;
> >  	prev_reg = buf[dsb->ins_start_offset + 1] & DSB_REG_VALUE_MASK;
> >
> > --
> > 2.39.3