> -----Original Message-----
> From: Roper, Matthew D <matthew.d.roper@xxxxxxxxx>
> Sent: Tuesday, August 17, 2021 3:42 AM
> To: Siddiqui, Ayaz A <ayaz.siddiqui@xxxxxxxxx>
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH V2 4/5] drm/i915/gt: Initialize unused MOCS
> entries with device specific values
>
> On Mon, Aug 16, 2021 at 10:22:28AM +0530, Ayaz A Siddiqui wrote:
> > During to creation mocs table,used field of drm_i915_mocs_entry is
> > being checked, if used field is 0, then it will check values of index
> > 1. All the unspecified indexes of xxx_mocs_table[] will contain
> > control value and l3cc value of index I915_MOCS_PTE if its
> > initialized.
>
> I think there might be some words missing in the description here; I'm having
> a bit of trouble following what it's saying. Maybe something like this would
> be more clear:
>
> Historically we've initialized all undefined/reserved entries in
> a platform's MOCS table to the contents of table entry #1 (i.e.,
> I915_MOCS_PTE).
>
> >
> > This patch is intended to provide capability to program device
> > specific control value and l3cc value index which can be used for all
> > the unspecified indexes of MOCS table.
>
> And maybe for this part
>
> Going forward, we can't assume that table entry #1 will always
> contain suitable values to use for undefined/reserved table
> indices. We'll allow a platform-specific table index to be
> selected at table initialization time in these cases.
>
> We should also make some mention about using this new mechanism to
> select an L3 WB entry for DG1 and all new platforms going forward, but note
> that we can't change our production gen12 platforms (TGL and RKL) since
> that would be an ABI break.
Thanks Matt for suggesting the better commit message,
will take care in next version.
>
> >
> > Signed-off-by: Ayaz A Siddiqui <ayaz.siddiqui@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gt/intel_mocs.c | 38
> > +++++++++++++++-------------
> > 1 file changed, 20 insertions(+), 18 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_mocs.c
> > b/drivers/gpu/drm/i915/gt/intel_mocs.c
> > index df3c5d550c46a..cf00537ba4acc 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_mocs.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_mocs.c
> > @@ -23,6 +23,7 @@ struct drm_i915_mocs_table {
> > unsigned int n_entries;
> > const struct drm_i915_mocs_entry *table;
> > u8 uc_index;
> > + u8 unused_entries_index;
> > };
> >
> > struct drm_i915_aux_table {
> > @@ -99,17 +100,23 @@ struct drm_i915_aux_table {
> > * Entries not part of the following tables are undefined as far as
> > * userspace is concerned and shouldn't be relied upon. For Gen < 12
> > * they will be initialized to PTE. Gen >= 12 onwards don't have a
> > setting for
> > - * PTE and will be initialized to an invalid value.
> > + * PTE and will be initialized L3 WB to catch accidental use of
> > + reserved and
> > + * unused mocs indexes.
>
> This comment doesn't seem to be quite true for all graphics ver >= 12
> platforms; TGL/RKL are still using an I915_MOCS_PTE setting (which is L3
> uncached) since we can't change it now without breaking ABI. Same for the
> NOTE2 below.
Sure I'll change it to "Gen12 onward excerpt TGL/RKL".
Regards
-Ayaz
>
>
> Matt
>
> > *
> > * The last few entries are reserved by the hardware. For ICL+ they
> > * should be initialized according to bspec and never used, for older
> > * platforms they should never be written to.
> > *
> > - * NOTE: These tables are part of bspec and defined as part of
> > hardware
> > + * NOTE1: These tables are part of bspec and defined as part of
> > + hardware
> > * interface for ICL+. For older platforms, they are part of kernel
> > * ABI. It is expected that, for specific hardware platform, existing
> > * entries will remain constant and the table will only be updated by
> > * adding new entries, filling unused positions.
> > + *
> > + * NOTE2: For GEN >= 12, reserved and unspecified MOCS indices have
> been
> > + * set to L3 WB. These reserved entries should never be used, they
> > + * may be changed to low performant variants with better coherency
> > + * in the future if more entries are needed.
> > */
> > #define GEN9_MOCS_ENTRIES \
> > MOCS_ENTRY(I915_MOCS_UNCACHED, \
> > @@ -292,17 +299,9 @@ static const struct drm_i915_mocs_entry
> > icl_mocs_table[] = { };
> >
> > static const struct drm_i915_mocs_entry dg1_mocs_table[] = {
> > - /* Error */
> > - MOCS_ENTRY(0, 0, L3_0_DIRECT),
> >
> > /* UC */
> > MOCS_ENTRY(1, 0, L3_1_UC),
> > -
> > - /* Reserved */
> > - MOCS_ENTRY(2, 0, L3_0_DIRECT),
> > - MOCS_ENTRY(3, 0, L3_0_DIRECT),
> > - MOCS_ENTRY(4, 0, L3_0_DIRECT),
> > -
> > /* WB - L3 */
> > MOCS_ENTRY(5, 0, L3_3_WB),
> > /* WB - L3 50% */
> > @@ -450,6 +449,7 @@ static unsigned int get_mocs_settings(const struct
> drm_i915_private *i915,
> > table->table = dg1_mocs_table;
> > table->n_entries = GEN9_NUM_MOCS_ENTRIES;
> > table->uc_index = 1;
> > + table->unused_entries_index = 5;
> > } else if (GRAPHICS_VER(i915) >= 12) {
> > table->size = ARRAY_SIZE(tgl_mocs_table);
> > table->table = tgl_mocs_table;
> > @@ -500,16 +500,17 @@ static unsigned int get_mocs_settings(const
> > struct drm_i915_private *i915, }
> >
> > /*
> > - * Get control_value from MOCS entry taking into account when it's not
> used:
> > - * I915_MOCS_PTE's value is returned in this case.
> > + * Get control_value from MOCS entry taking into account when it's
> > + not used
> > + * then if unused_entries_index is non-zero then its value will be
> > + returned
> > + * otherwise I915_MOCS_PTE's value is returned in this case.
> > */
> > static u32 get_entry_control(const struct drm_i915_mocs_table *table,
> > unsigned int index)
> > {
> > if (index < table->size && table->table[index].used)
> > return table->table[index].control_value;
> > -
> > - return table->table[I915_MOCS_PTE].control_value;
> > + index = table->unused_entries_index ? : I915_MOCS_PTE;
> > + return table->table[index].control_value;
> > }
> >
> > #define for_each_mocs(mocs, t, i) \
> > @@ -550,16 +551,17 @@ static void init_mocs_table(struct
> > intel_engine_cs *engine, }
> >
> > /*
> > - * Get l3cc_value from MOCS entry taking into account when it's not used:
> > - * I915_MOCS_PTE's value is returned in this case.
> > + * Get l3cc_value from MOCS entry taking into account when it's not
> > + used
> > + * then if unused_entries_index is not zero then its value will be
> > + returned
> > + * otherwise I915_MOCS_PTE's value is returned in this case.
> > */
> > static u16 get_entry_l3cc(const struct drm_i915_mocs_table *table,
> > unsigned int index)
> > {
> > if (index < table->size && table->table[index].used)
> > return table->table[index].l3cc_value;
> > -
> > - return table->table[I915_MOCS_PTE].l3cc_value;
> > + index = table->unused_entries_index ? : I915_MOCS_PTE;
> > + return table->table[index].l3cc_value;
> > }
> >
> > static u32 l3cc_combine(u16 low, u16 high)
> > --
> > 2.26.2
> >
>
> --
> Matt Roper
> Graphics Software Engineer
> VTT-OSGC Platform Enablement
> Intel Corporation
> (916) 356-2795
