[PATCH v2 1/1] drm/xe: correct the calculation of remaining size

[Yang, Fei]

> On Tue, Jan 16, 2024 at 12:04:24PM -0800, fei.yang at intel.com wrote:
>> From: Fei Yang <fei.yang at intel.com>
>>
>> In function write_pgtable, the calculation of chunk in the do-while
>> loop is wrong, we should always compare against remaining size instead
>> of the total size update->qwords.
>> Also, when performing dword writes, dword length can be any value from
>> 2 to 3fe, always adding 1 is wrong.
>
> Always adding 1 should be correct.  This field holds the number of dwords
> for the instruction as a whole (encoded in n-2 format as it is for all GPU
> instructions), not the number of dwords being stored by the command.  The
> instruction always includes three initial dwords (1 for the instruction header,
> 2 for the target address).  So if you want to store n dwords, the total
> instruction length is n+3 which means the encoded field contents are n+1.

But according to the bspec, what you said only applies to qword writes (bit21 set),
not dword writes. So, MI_SDI_NUM_QW looks correct, MI_SDI_NUM_DW is not.
Am I misunderstanding?

>
>Matt
>
>>
>> Signed-off-by: Fei Yang <fei.yang at intel.com>
>> ---
>>  drivers/gpu/drm/xe/instructions/xe_mi_commands.h | 2 +-
>>  drivers/gpu/drm/xe/xe_migrate.c                  | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/instructions/xe_mi_commands.h
>> b/drivers/gpu/drm/xe/instructions/xe_mi_commands.h
>> index c74ceb550dce..415609b070fb 100644
>> --- a/drivers/gpu/drm/xe/instructions/xe_mi_commands.h
>> +++ b/drivers/gpu/drm/xe/instructions/xe_mi_commands.h
>> @@ -36,7 +36,7 @@
>>  #define MI_STORE_DATA_IMM           __MI_INSTR(0x20)
>>  #define   MI_SDI_GGTT                       REG_BIT(22)
>>  #define   MI_SDI_LEN_DW                     GENMASK(9, 0)
>> -#define   MI_SDI_NUM_DW(x)          REG_FIELD_PREP(MI_SDI_LEN_DW, (x) + 3 - 2)
>> +#define   MI_SDI_NUM_DW(x)          REG_FIELD_PREP(MI_SDI_LEN_DW, ((x) > 1) ? (x) : 2)
>>  #define   MI_SDI_NUM_QW(x)          (REG_FIELD_PREP(MI_SDI_LEN_DW, 2 * (x) + 3 - 2) | \
>>                                       REG_BIT(21))
>>
>> diff --git a/drivers/gpu/drm/xe/xe_migrate.c
>> b/drivers/gpu/drm/xe/xe_migrate.c index 44725f978f3e..d5392cbbdb49
>> 100644
>> --- a/drivers/gpu/drm/xe/xe_migrate.c
>> +++ b/drivers/gpu/drm/xe/xe_migrate.c
>> @@ -1116,7 +1116,7 @@ static void write_pgtable(struct xe_tile *tile, struct xe_bb *bb, u64 ppgtt_ofs,
>>      do {
>>              u64 addr = ppgtt_ofs + ofs * 8;
>>
>> -            chunk = min(update->qwords, MAX_PTE_PER_SDI);
>> +            chunk = min(size, MAX_PTE_PER_SDI);
>>
>>              /* Ensure populatefn can do memset64 by aligning bb->cs */
>>              if (!(bb->len & 1))
>> --
>> 2.25.1
>>
>
> --
> Matt Roper
> Graphics Software Engineer
> Linux GPU Platform Enablement
> Intel Corporation