Re: [PATCH v3 3/3] drm/i915: Give proper names to MOCS entries

[Zhao Yakui <yakui.zhao@intel.com>]

On 07/01/2016 09:40 PM, Deak, Imre wrote:
> The purpose for each MOCS entry isn't well defined atm. Defining these
> is important to remove any uncertainty about the use of these entries
> for example in terms of performance and GPU/CPU coherency.
>
> Suggested by Ville.
>
> CC: Rong R Yang<rong.r.yang@intel.com>
> CC: Yakui Zhao<yakui.zhao@intel.com>
> CC: Ville Syrjälä<ville.syrjala@linux.intel.com>
> CC: Chris Wilson<chris@chris-wilson.co.uk>
> Signed-off-by: Imre Deak<imre.deak@intel.com>

This looks readable and meaningful after giving proper names to MOCS 
entry index.

But not sure whether the comment of I915_MOCS_CACHE has one typo?

> ---
>   drivers/gpu/drm/i915/intel_mocs.c | 13 +++++++------
>   include/uapi/drm/i915_drm.h       | 24 ++++++++++++++++++++++++
>   2 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_mocs.c b/drivers/gpu/drm/i915/intel_mocs.c
> index 927825f..86adc11 100644
> --- a/drivers/gpu/drm/i915/intel_mocs.c
> +++ b/drivers/gpu/drm/i915/intel_mocs.c
> @@ -97,7 +97,8 @@ struct drm_i915_mocs_table {
>    *       end.
>    */
>   static const struct drm_i915_mocs_entry skylake_mocs_table[] = {
> -	{ /* 0x00000009 */
> +	[I915_MOCS_UNCACHED] = {
> +	  /* 0x00000009 */
>   	  .control_value = LE_CACHEABILITY(LE_UC) |
>   			   LE_TGT_CACHE(LE_TC_LLC_ELLC) |
>   			   LE_LRUM(0) | LE_AOM(0) | LE_RSC(0) | LE_SCC(0) |
> @@ -106,7 +107,7 @@ static const struct drm_i915_mocs_entry skylake_mocs_table[] = {
>   	  /* 0x0010 */
>   	  .l3cc_value =    L3_ESC(0) | L3_SCC(0) | L3_CACHEABILITY(L3_UC),
>   	},
> -	{
> +	[I915_MOCS_AUTO] = {
>   	  /* 0x00000038 */
>   	  .control_value = LE_CACHEABILITY(LE_PAGETABLE) |
>   			   LE_TGT_CACHE(LE_TC_LLC_ELLC) |
> @@ -115,7 +116,7 @@ static const struct drm_i915_mocs_entry skylake_mocs_table[] = {
>   	  /* 0x0030 */
>   	  .l3cc_value =    L3_ESC(0) | L3_SCC(0) | L3_CACHEABILITY(L3_WB),
>   	},
> -	{
> +	[I915_MOCS_CACHED] = {
>   	  /* 0x0000003b */
>   	  .control_value = LE_CACHEABILITY(LE_WB) |
>   			   LE_TGT_CACHE(LE_TC_LLC_ELLC) |
> @@ -128,7 +129,7 @@ static const struct drm_i915_mocs_entry skylake_mocs_table[] = {
>
>   /* NOTE: the LE_TGT_CACHE is not used on Broxton */
>   static const struct drm_i915_mocs_entry broxton_mocs_table[] = {
> -	{
> +	[I915_MOCS_UNCACHED] = {
>   	  /* 0x00000009 */
>   	  .control_value = LE_CACHEABILITY(LE_UC) |
>   			   LE_TGT_CACHE(LE_TC_LLC_ELLC) |
> @@ -138,7 +139,7 @@ static const struct drm_i915_mocs_entry broxton_mocs_table[] = {
>   	  /* 0x0010 */
>   	  .l3cc_value =    L3_ESC(0) | L3_SCC(0) | L3_CACHEABILITY(L3_UC),
>   	},
> -	{
> +	[I915_MOCS_AUTO] = {
>   	  /* 0x00000038 */
>   	  .control_value = LE_CACHEABILITY(LE_PAGETABLE) |
>   			   LE_TGT_CACHE(LE_TC_LLC_ELLC) |
> @@ -148,7 +149,7 @@ static const struct drm_i915_mocs_entry broxton_mocs_table[] = {
>   	  /* 0x0030 */
>   	  .l3cc_value =    L3_ESC(0) | L3_SCC(0) | L3_CACHEABILITY(L3_WB),
>   	},
> -	{
> +	[I915_MOCS_CACHED] = {
>   	  /* 0x00000039 */
>   	  .control_value = LE_CACHEABILITY(LE_UC) |
>   			   LE_TGT_CACHE(LE_TC_LLC_ELLC) |
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index c17d63d..a5d116f 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -62,6 +62,30 @@ extern "C" {
>   #define I915_ERROR_UEVENT		"ERROR"
>   #define I915_RESET_UEVENT		"RESET"
>
> +/*
> + * MOCS indexes used for GPU surfaces, defining the cacheability of the
> + * surface data and the coherency for this data wrt. CPU vs. GPU accesses.
> + */
> +enum i915_mocs_table_index {
> +	/*
> +	 * Not cached anywhere, coherency between CPU and GPU accesses is
> +	 * guaranteed.
> +	 */
> +	I915_MOCS_UNCACHED,
> +	/*
> +	 * Cacheability and coherency controlled by the kernel automatically
> +	 * based on the DRM_I915_GEM_SET_CACHING IOCTL setting and the current
> +	 * usage of the surface (used for display scanout or not).
> +	 */
> +	I915_MOCS_AUTO,
> +	/*
> +	 * Cached in all GPU caches available on the platform.
> +	 * Coherency between CPU and GPU accesses to the surface is not
> +	 * guaranteed without extra synchronization.
> +	 */

IMO the coherency is guaranteed without extra synchronization for the 
MOCS_CACHED.

> +	I915_MOCS_CACHED,
> +};
> +
>   /* Each region is a minimum of 16k, and there are at most 255 of them.
>    */
>   #define I915_NR_TEX_REGIONS 255	/* table size 2k - maximum due to use

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