On Fri, Sep 16, 2022 at 10:02:32AM +0100, Tvrtko Ursulin wrote:
>
> On 16/09/2022 02:43, Matt Roper wrote:
> > Although the bspec lists several MMIO ranges as "MSLICE," it turns out
> > that a subset of these are of a "GAM" subclass that has unique rules and
> > doesn't followed regular mslice steering behavior.
> >
> > * Xe_HP SDV: GAM ranges must always be steered to 0,0. These
> > registers share the regular steering control register (0xFDC) with
> > other steering types
> >
> > * DG2: GAM ranges must always be steered to 1,0. GAM registers have a
> > dedicated steering control register (0xFE0) so we can set the value
> > once at startup and rely on implicit steering. Technically the
> > hardware default should already be set to 1,0 properly, but it never
> > hurts to ensure that in the driver.
>
> Do you have any data on whether the "technically should" holds in practice?
> What would be the consequences of some platform/machine surprising us here?
The bspec indicates the hardware default value is already the necessary
1,0 value; I'm mostly paranoid about some kind of boot firmware wiping
it to 0,0 by accident. I don't have any evidence that has ever actually
happened, but explicitly re-programming it to 1,0 in the patch here is a
defensive measure just to be safe.
If we didn't have this patch _and_ some firmware screwed up the GAM
steering target, then presumably we might read back garbage or 0 from
GAM registers in places where we should have received a real value.
Matt
>
> Regards,
>
> Tvrtko
>
> >
> > Bspec: 66534
> > Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 24 +++++++++++++++++++--
> > drivers/gpu/drm/i915/gt/intel_gt_regs.h | 1 +
> > drivers/gpu/drm/i915/gt/intel_gt_types.h | 1 +
> > drivers/gpu/drm/i915/gt/intel_workarounds.c | 10 +++++++++
> > 4 files changed, 34 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
> > index e79405a45312..a2047a68ea7a 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c
> > @@ -40,6 +40,7 @@ static const char * const intel_steering_types[] = {
> > "L3BANK",
> > "MSLICE",
> > "LNCF",
> > + "GAM",
> > "INSTANCE 0",
> > };
> > @@ -48,14 +49,23 @@ static const struct intel_mmio_range icl_l3bank_steering_table[] = {
> > {},
> > };
> > +/*
> > + * Although the bspec lists more "MSLICE" ranges than shown here, some of those
> > + * are of a "GAM" subclass that has special rules. Thus we use a separate
> > + * GAM table farther down for those.
> > + */
> > static const struct intel_mmio_range xehpsdv_mslice_steering_table[] = {
> > - { 0x004000, 0x004AFF },
> > - { 0x00C800, 0x00CFFF },
> > { 0x00DD00, 0x00DDFF },
> > { 0x00E900, 0x00FFFF }, /* 0xEA00 - OxEFFF is unused */
> > {},
> > };
> > +static const struct intel_mmio_range xehpsdv_gam_steering_table[] = {
> > + { 0x004000, 0x004AFF },
> > + { 0x00C800, 0x00CFFF },
> > + {},
> > +};
> > +
> > static const struct intel_mmio_range xehpsdv_lncf_steering_table[] = {
> > { 0x00B000, 0x00B0FF },
> > { 0x00D800, 0x00D8FF },
> > @@ -114,9 +124,15 @@ void intel_gt_mcr_init(struct intel_gt *gt)
> > } else if (IS_DG2(i915)) {
> > gt->steering_table[MSLICE] = xehpsdv_mslice_steering_table;
> > gt->steering_table[LNCF] = dg2_lncf_steering_table;
> > + /*
> > + * No need to hook up the GAM table since it has a dedicated
> > + * steering control register on DG2 and can use implicit
> > + * steering.
> > + */
> > } else if (IS_XEHPSDV(i915)) {
> > gt->steering_table[MSLICE] = xehpsdv_mslice_steering_table;
> > gt->steering_table[LNCF] = xehpsdv_lncf_steering_table;
> > + gt->steering_table[GAM] = xehpsdv_gam_steering_table;
> > } else if (GRAPHICS_VER(i915) >= 11 &&
> > GRAPHICS_VER_FULL(i915) < IP_VER(12, 50)) {
> > gt->steering_table[L3BANK] = icl_l3bank_steering_table;
> > @@ -351,6 +367,10 @@ static void get_nonterminated_steering(struct intel_gt *gt,
> > *group = __ffs(gt->info.mslice_mask) << 1;
> > *instance = 0; /* unused */
> > break;
> > + case GAM:
> > + *group = IS_DG2(gt->i915) ? 1 : 0;
> > + *instance = 0;
> > + break;
> > case INSTANCE0:
> > /*
> > * There are a lot of MCR types for which instance (0, 0)
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_regs.h b/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > index 2275ee47da95..2343b26e0e21 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_regs.h
> > @@ -42,6 +42,7 @@
> > #define MCFG_MCR_SELECTOR _MMIO(0xfd0)
> > #define SF_MCR_SELECTOR _MMIO(0xfd8)
> > #define GEN8_MCR_SELECTOR _MMIO(0xfdc)
> > +#define GAM_MCR_SELECTOR _MMIO(0xfe0)
> > #define GEN8_MCR_SLICE(slice) (((slice) & 3) << 26)
> > #define GEN8_MCR_SLICE_MASK GEN8_MCR_SLICE(3)
> > #define GEN8_MCR_SUBSLICE(subslice) (((subslice) & 3) << 24)
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_types.h b/drivers/gpu/drm/i915/gt/intel_gt_types.h
> > index f19c2de77ff6..30003d68fd51 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_types.h
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_types.h
> > @@ -59,6 +59,7 @@ enum intel_steering_type {
> > L3BANK,
> > MSLICE,
> > LNCF,
> > + GAM,
> > /*
> > * On some platforms there are multiple types of MCR registers that
> > diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > index 6d2003d598e6..d04652a3b4e5 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> > @@ -1181,6 +1181,9 @@ xehp_init_mcr(struct intel_gt *gt, struct i915_wa_list *wal)
> > gt->steering_table[MSLICE] = NULL;
> > }
> > + if (IS_XEHPSDV(gt->i915) && slice_mask & BIT(0))
> > + gt->steering_table[GAM] = NULL;
> > +
> > slice = __ffs(slice_mask);
> > subslice = intel_sseu_find_first_xehp_dss(sseu, GEN_DSS_PER_GSLICE, slice) %
> > GEN_DSS_PER_GSLICE;
> > @@ -1198,6 +1201,13 @@ xehp_init_mcr(struct intel_gt *gt, struct i915_wa_list *wal)
> > */
> > __set_mcr_steering(wal, MCFG_MCR_SELECTOR, 0, 2);
> > __set_mcr_steering(wal, SF_MCR_SELECTOR, 0, 2);
> > +
> > + /*
> > + * On DG2, GAM registers have a dedicated steering control register
> > + * and must always be programmed to a hardcoded groupid of "1."
> > + */
> > + if (IS_DG2(gt->i915))
> > + __set_mcr_steering(wal, GAM_MCR_SELECTOR, 1, 0);
> > }
> > static void
--
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
