> -----Original Message----- > From: Manna, Animesh > Sent: Wednesday, July 5, 2023 3:10 PM > To: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>; intel- > gfx@xxxxxxxxxxxxxxxxxxxxx > Subject: RE: [PATCH v2 06/19] drm/i915/dsb: Avoid corrupting the > first register write > > > > > -----Original Message----- > > From: Intel-gfx <intel-gfx-bounces@xxxxxxxxxxxxxxxxxxxxx> On Behalf Of > > Ville Syrjala > > Sent: Wednesday, June 7, 2023 12:45 AM > > To: intel-gfx@xxxxxxxxxxxxxxxxxxxxx > > Subject: [PATCH v2 06/19] drm/i915/dsb: Avoid corrupting > > the first register write > > > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > 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@xxxxxxxxxxxxxxx> > > LGTM. > Signed-off-by: Animesh Manna <animesh.manna@xxxxxxxxx> Correction! By mistake added my Signed-off-by. Reviewed-by: Animesh Manna <animesh.manna@xxxxxxxxx> > > > --- > > 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
