Quoting Souza, Jose (2020-02-22 00:36:53)
> + CCing people involved in the patch fixed.
>
> On Fri, 2020-02-21 at 16:28 -0800, Lucas De Marchi wrote:
> > Wa_1608008084 is an additional WA that applies to writes on FF_MODE2
> > register. We can't read it back either from CPU or GPU. Since the
> > other
> > bits should be 0, recommendation to handle Wa_1604555607 is to
> > actually
> > just write the timer value.
> >
> > Do a write only and don't try to read it, neither before or after
> > the WA is applied.
> >
> > Fixes: ff690b2111ba ("drm/i915/tgl: Implement Wa_1604555607")
> > Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_workarounds.c | 22 ++++++++++---------
> > --
> > 1 file changed, 10 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > index 887e0dc701f7..0d76e1d6ec87 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > @@ -580,24 +580,22 @@ static void icl_ctx_workarounds_init(struct
> > intel_engine_cs *engine,
> > static void tgl_ctx_workarounds_init(struct intel_engine_cs *engine,
> > struct i915_wa_list *wal)
> > {
> > - u32 val;
> > -
> > /* Wa_1409142259:tgl */
> > WA_SET_BIT_MASKED(GEN11_COMMON_SLICE_CHICKEN3,
> > GEN12_DISABLE_CPS_AWARE_COLOR_PIPE);
> >
> > - /* Wa_1604555607:tgl */
> > - val = intel_uncore_read(engine->uncore, FF_MODE2);
> > - val &= ~FF_MODE2_TDS_TIMER_MASK;
> > - val |= FF_MODE2_TDS_TIMER_128;
> > /*
> > - * FIXME: FF_MODE2 register is not readable till TGL B0. We can
> > - * enable verification of WA from the later steppings, which
> > enables
> > - * the read of FF_MODE2.
> > + * Wa_1604555607:gen12
> > + * FF_MODE2 register is not readable till TGL B0, either by CPU
> > or GPU.
>
> The line above could be removed as the comments above explain it
> better, also BSpec don't say that it will be fixed in B0.
The HW guys on discovering the bug promised it would be fixed for B0.
-Chris
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