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

[Matt Roper]

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.


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