Re: [PATCH v7 3/4] drm/i915/icl: Define MOCS table for Icelake

["Lis, Tomasz" <tomasz.lis@xxxxxxxxx>]

On 2018-12-21 13:29, Tvrtko Ursulin wrote:
> On 14/12/2018 18:20, Lucas De Marchi wrote:
> > From: Tomasz Lis <tomasz.lis@xxxxxxxxx>
> >
> > The table has been unified across OSes to minimize virtualization 
> > overhead.
> >
> > The MOCS table is now published as part of bspec, and versioned. Entries
> > are supposed to never be modified, but new ones can be added. Adding
> > entries increases table version. The patch includes version 1 entries.
> >
> > Meaning of each entry is now explained in bspec, and user mode clients
> > are expected to know what each entry means. The 3 entries used for 
> > previous
> > platforms are still compatible with their legacy definitions, but 
> > that is
> > not guaranteed to be true for future platforms.
> >
> > v2: Fixed SCC values, improved commit comment (Daniele)
> > v3: Improved MOCS table comment (Daniele)
> > v4: Moved new entries below gen9 ones. Put common entries into
> >      definition to be used in multiple arrays. (Lucas)
> > v5: Made defines for or-ing flags. Renamed macros from MOCS_TABLE
> >      to MOCS_ENTRIES. Switched LE_CoS to upper case. (Joonas)
> > v6: Removed definitions of reserved entries. (Michal)
> >      Increased limit of entries sent to the hardware on gen11+.
> > v7: Simplify table as done for previou gens (Lucas)
> >
> > BSpec: 34007
> > BSpec: 560
> >
> > Signed-off-by: Tomasz Lis <tomasz.lis@xxxxxxxxx>
> > Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@xxxxxxxxx>
> > Reviewed-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> > Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/intel_mocs.c | 187 ++++++++++++++++++++++++++----
> >   1 file changed, 162 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_mocs.c 
> > b/drivers/gpu/drm/i915/intel_mocs.c
> > index 577633cefb8a..dfc4edea020f 100644
> > --- a/drivers/gpu/drm/i915/intel_mocs.c
> > +++ b/drivers/gpu/drm/i915/intel_mocs.c
> > @@ -44,6 +44,8 @@ struct drm_i915_mocs_table {
> >   #define LE_SCC(value)        ((value) << 8)
> >   #define LE_PFM(value)        ((value) << 11)
> >   #define LE_SCF(value)        ((value) << 14)
> > +#define LE_COS(value)        ((value) << 15)
> > +#define LE_SSE(value)        ((value) << 17)
> >     /* Defines for the tables (LNCFMOCS0 - LNCFMOCS31) - two entries 
> > per word */
> >   #define L3_ESC(value)        ((value) << 0)
> > @@ -52,6 +54,10 @@ struct drm_i915_mocs_table {
> >     /* Helper defines */
> >   #define GEN9_NUM_MOCS_ENTRIES    62  /* 62 out of 64 - 63 & 64 are 
> > reserved. */
> > +#define GEN11_NUM_MOCS_ENTRIES    64  /* 63-64 are reserved, but 
> > configured. */
> > +
> > +#define NUM_MOCS_ENTRIES(i915) \
> > +    (INTEL_GEN(i915) < 11 ? GEN9_NUM_MOCS_ENTRIES : 
> > GEN11_NUM_MOCS_ENTRIES)
> >     /* (e)LLC caching options */
> >   #define LE_0_PAGETABLE        _LE_CACHEABILITY(0)
> > @@ -80,21 +86,21 @@ struct drm_i915_mocs_table {
> >    * LNCFCMOCS0 - LNCFCMOCS32 registers.
> >    *
> >    * These tables are intended to be kept reasonably consistent across
> > - * platforms. However some of the fields are not applicable to all of
> > - * them.
> > + * HW platforms, and for ICL+, be identical across OSes. To achieve
> > + * that, for Icelake and above, list of entries is published as part
> > + * of bspec.
> >    *
> >    * Entries not part of the following tables are undefined as far as
> > - * userspace is concerned and shouldn't be relied upon.  For the time
> > - * being they will be implicitly initialized to the strictest caching
> > - * configuration (uncached) to guarantee forwards compatibility with
> > - * userspace programs written against more recent kernels providing
> > - * additional MOCS entries.
> > + * userspace is concerned and shouldn't be relied upon.
> > + *
> > + * The last two 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 MUST start with being uncached and the length
> > - *       MUST be less than 63 as the last two registers are reserved
> > - *       by the hardware.  These tables are part of the kernel ABI and
> > - *       may only be updated incrementally by adding entries at the
> > - *       end.
> > + * NOTE: 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 existing entries will remain constant
> > + *       and the tables will only be updated by adding new entries.
> >    */
> >     #define GEN9_MOCS_ENTRIES \
> > @@ -132,6 +138,132 @@ static const struct drm_i915_mocs_entry 
> > broxton_mocs_table[] = {
> >       },
> >   };
> >   +#define GEN11_MOCS_ENTRIES \
> > +    [0] = { \
> > +        /* Base - Uncached (Deprecated) */ \
> > +        .control_value = LE_1_UC | LE_TC_1_LLC, \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [1] = { \
> > +        /* Base - L3 + LeCC:PAT (Deprecated) */ \
> > +        .control_value = LE_0_PAGETABLE | LE_TC_1_LLC, \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [2] = { \
> > +        /* Base - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [3] = { \
> > +        /* Base - Uncached */ \
> > +        .control_value = LE_1_UC | LE_TC_1_LLC, \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [4] = { \
> > +        /* Base - L3 */ \
> > +        .control_value = LE_1_UC | LE_TC_1_LLC, \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [5] = { \
> > +        /* Base - LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [6] = { \
> > +        /* Age 0 - LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(1), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [7] = { \
> > +        /* Age 0 - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(1), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [8] = { \
> > +        /* Age: Don't Chg. - LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(2), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [9] = { \
> > +        /* Age: Don't Chg. - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(2), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [10] = { \
> > +        /* No AOM - LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_AOM(1), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [11] = { \
> > +        /* No AOM - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_AOM(1), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [12] = { \
> > +        /* No AOM; Age 0 - LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(1) | 
> > LE_AOM(1), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [13] = { \
> > +        /* No AOM; Age 0 - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(1) | 
> > LE_AOM(1), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [14] = { \
> > +        /* No AOM; Age:DC - LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(2) | 
> > LE_AOM(1), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [15] = { \
> > +        /* No AOM; Age:DC - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(2) | 
> > LE_AOM(1), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [18] = { \
> > +        /* Self-Snoop - L3 + LLC */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_SSE(3), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [19] = { \
> > +        /* Skip Caching - L3 + LLC(12.5%) */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_SCC(7), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [20] = { \
> > +        /* Skip Caching - L3 + LLC(25%) */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_SCC(3), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [21] = { \
> > +        /* Skip Caching - L3 + LLC(50%) */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_SCC(1), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [22] = { \
> > +        /* Skip Caching - L3 + LLC(75%) */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_RSC(1) | LE_SCC(3), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
> > +    [23] = { \
> > +        /* Skip Caching - L3 + LLC(87.5%) */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3) | 
> > LE_RSC(1) | LE_SCC(7), \
> > +        .l3cc_value = L3_3_WB \
> > +    }, \
>
> There is a hole of unused entries here which I think comes to play 
> from the emit functions later.
>
> > +    [62] = { \
> > +        /* HW Reserved - SW program but never use */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3), \
> > +        .l3cc_value = L3_1_UC \
> > +    }, \
> > +    [63] = { \
> > +        /* HW Reserved - SW program but never use */ \
> > +        .control_value = LE_3_WB | LE_TC_1_LLC | LE_LRUM(3), \
> > +        .l3cc_value = L3_1_UC \
> > +    },
> > +
> > +static const struct drm_i915_mocs_entry icelake_mocs_table[] = {
> > +    GEN11_MOCS_ENTRIES
> > +};
> > +
> >   /**
> >    * get_mocs_settings()
> >    * @dev_priv:    i915 device.
> > @@ -149,8 +281,11 @@ static bool get_mocs_settings(struct 
> > drm_i915_private *dev_priv,
> >   {
> >       bool result = false;
> >   -    if (IS_GEN9_BC(dev_priv) || IS_CANNONLAKE(dev_priv) ||
> > -        IS_ICELAKE(dev_priv)) {
> > +    if (IS_ICELAKE(dev_priv)) {
> > +        table->size  = ARRAY_SIZE(icelake_mocs_table);
>
> So effectively this is always 64 due last two reserved entries.
>
> > +        table->table = icelake_mocs_table;
> > +        result = true;
> > +    } else if (IS_GEN9_BC(dev_priv) || IS_CANNONLAKE(dev_priv)) {
> >           table->size  = ARRAY_SIZE(skylake_mocs_table);
> >           table->table = skylake_mocs_table;
> >           result = true;
> > @@ -213,7 +348,7 @@ void intel_mocs_init_engine(struct 
> > intel_engine_cs *engine)
> >       if (!get_mocs_settings(dev_priv, &table))
> >           return;
> >   -    GEM_BUG_ON(table.size > GEN9_NUM_MOCS_ENTRIES);
> > +    GEM_BUG_ON(table.size > NUM_MOCS_ENTRIES(dev_priv));
> >         for (index = 0; index < table.size; index++)
> >           I915_WRITE(mocs_register(engine->id, index),
> > @@ -227,7 +362,7 @@ void intel_mocs_init_engine(struct 
> > intel_engine_cs *engine)
> >        * Entry 0 in the table is uncached - so we are just writing
> >        * that value to all the used entries.
> >        */
> > -    for (; index < GEN9_NUM_MOCS_ENTRIES; index++)
> > +    for (; index < NUM_MOCS_ENTRIES(dev_priv); index++)
> >           I915_WRITE(mocs_register(engine->id, index),
> >                  table.table[0].control_value);
> >   }
> > @@ -245,18 +380,19 @@ void intel_mocs_init_engine(struct 
> > intel_engine_cs *engine)
> >   static int emit_mocs_control_table(struct i915_request *rq,
> >                      const struct drm_i915_mocs_table *table)
> >   {
> > +    struct drm_i915_private *i915 = rq->i915;
> >       enum intel_engine_id engine = rq->engine->id;
> >       unsigned int index;
> >       u32 *cs;
> >   -    if (WARN_ON(table->size > GEN9_NUM_MOCS_ENTRIES))
> > +    if (WARN_ON(table->size > NUM_MOCS_ENTRIES(i915)))
> >           return -ENODEV;
> >   -    cs = intel_ring_begin(rq, 2 + 2 * GEN9_NUM_MOCS_ENTRIES);
> > +    cs = intel_ring_begin(rq, 2 + 2 * NUM_MOCS_ENTRIES(i915));
> >       if (IS_ERR(cs))
> >           return PTR_ERR(cs);
> >   -    *cs++ = MI_LOAD_REGISTER_IMM(GEN9_NUM_MOCS_ENTRIES);
> > +    *cs++ = MI_LOAD_REGISTER_IMM(NUM_MOCS_ENTRIES(i915));
> >         for (index = 0; index < table->size; index++) {
> >           *cs++ = i915_mmio_reg_offset(mocs_register(engine, index));
> > @@ -271,7 +407,7 @@ static int emit_mocs_control_table(struct 
> > i915_request *rq,
> >        * Entry 0 in the table is uncached - so we are just writing
> >        * that value to all the used entries.
> >        */
> > -    for (; index < GEN9_NUM_MOCS_ENTRIES; index++) {
> > +    for (; index < NUM_MOCS_ENTRIES(i915); index++) {
> >           *cs++ = i915_mmio_reg_offset(mocs_register(engine, index));
> >           *cs++ = table->table[0].control_value;
>
> So in init and emit functions the behaviour is now different due 
> reserved entries.
>
> Where before (and according the the comment which this patch removes - 
> why?) we were setting unused entries to uncached, on Icelake they will 
> be set to whatever all zeros is - LE_PAGETABLE?
>
> If that is not desired, we may need to transition to a scheme where 
> struct drm_i915_mocs_entry starts holding the table index, and the 
> static array is not indexed by it.
>
> It would also save the unused hole of zeros on Icelake which would 
> probably offset the extra used space.
>
> So I think someone needs to clarify what is the desired state for 
> unused entries on Icelake.
I don't think we have reason to care for the undefined entries. We do 
not give any promises regarding these entries. Any way we use to fill 
them will do, and we have no obligation not to change it later, in case 
a need emerges.

Since each entry is just 2 ints, adding index does not seem justified 
for me. We could add it as u16 next to the existing u16, and therefore 
not increase drm_i915_mocs_entry size at all (just use the bytes in 
padding); but having indexes also increases code complexity.

My opinion here is not really strong though, both indexed and 
non-indexed way will work for me.
-Tomasz

> Regards,
>
> Tvrtko
>
> >       }
> > @@ -304,17 +440,18 @@ static inline u32 l3cc_combine(const struct 
> > drm_i915_mocs_table *table,
> >   static int emit_mocs_l3cc_table(struct i915_request *rq,
> >                   const struct drm_i915_mocs_table *table)
> >   {
> > +    struct drm_i915_private *i915 = rq->i915;
> >       unsigned int i;
> >       u32 *cs;
> >   -    if (WARN_ON(table->size > GEN9_NUM_MOCS_ENTRIES))
> > +    if (WARN_ON(table->size > NUM_MOCS_ENTRIES(i915)))
> >           return -ENODEV;
> >   -    cs = intel_ring_begin(rq, 2 + GEN9_NUM_MOCS_ENTRIES);
> > +    cs = intel_ring_begin(rq, 2 + NUM_MOCS_ENTRIES(i915));
> >       if (IS_ERR(cs))
> >           return PTR_ERR(cs);
> >   -    *cs++ = MI_LOAD_REGISTER_IMM(GEN9_NUM_MOCS_ENTRIES / 2);
> > +    *cs++ = MI_LOAD_REGISTER_IMM(NUM_MOCS_ENTRIES(i915) / 2);
> >         for (i = 0; i < table->size/2; i++) {
> >           *cs++ = i915_mmio_reg_offset(GEN9_LNCFCMOCS(i));
> > @@ -333,7 +470,7 @@ static int emit_mocs_l3cc_table(struct 
> > i915_request *rq,
> >        * this will be uncached. Leave the last pair uninitialised as
> >        * they are reserved by the hardware.
> >        */
> > -    for (; i < GEN9_NUM_MOCS_ENTRIES / 2; i++) {
> > +    for (; i < NUM_MOCS_ENTRIES(i915) / 2; i++) {
> >           *cs++ = i915_mmio_reg_offset(GEN9_LNCFCMOCS(i));
> >           *cs++ = l3cc_combine(table, 0, 0);
> >       }
> > @@ -380,7 +517,7 @@ void intel_mocs_init_l3cc_table(struct 
> > drm_i915_private *dev_priv)
> >        * this will be uncached. Leave the last pair as initialised as
> >        * they are reserved by the hardware.
> >        */
> > -    for (; i < (GEN9_NUM_MOCS_ENTRIES / 2); i++)
> > +    for (; i < (NUM_MOCS_ENTRIES(dev_priv) / 2); i++)
> >           I915_WRITE(GEN9_LNCFCMOCS(i), l3cc_combine(&table, 0, 0));
> >   }

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