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

[Imre Deak <imre.deak@intel.com>]

On pe, 2016-07-01 at 14:49 +0100, Chris Wilson wrote:
> On Fri, Jul 01, 2016 at 04:40:06PM +0300, Imre Deak 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>
> > ---
> >  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,
> 
> So PTE.

Can change it.

> > +	/*
> > +	 * Cached in all GPU caches available on the platform.
> > +	 * Coherency between CPU and GPU accesses to the surface is not
> > +	 * guaranteed without extra synchronization.
> > +	 */
> > +	I915_MOCS_CACHED,
> 
> So pretty useless for its current usage then.

This is how it's used in Mesa atm where there is no need for coherency.
Beignet and Libva don't use this entry atm.

--Imre
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