Re: [PATCH 05/32] drm/i915/dram: Add field ecc_impacting_de

[Matt Atwood <matthew.s.atwood@intel.com>]

On Wed, Oct 15, 2025 at 05:46:52PM +0300, Jani Nikula wrote:
> On Wed, 15 Oct 2025, Gustavo Sousa <gustavo.sousa@intel.com> wrote:
> > Starting with Xe3p_LPD, we now have a new field in MEM_SS_INFO_GLOBAL
> > that indicates whether the memory has enabled ECC that limits display
> > bandwidth.  Add the field ecc_impacting_de to struct dram_info to
> > contain that information and set it appropriately when probing for
> > memory info.  We will use that field when updating bandwidth parameters
> > for Xe3p_LPD.
> 
> Could the field name be more accurate than "ecc impacting de"? It sounds
> quite handwavy to me.
I quite like it because it matches the field in the register on bspec.
MattA
> 
> BR,
> Jani.
> 
> >
> > Bspec: 69131
> > Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
> > ---
> >  drivers/gpu/drm/i915/i915_reg.h       | 1 +
> >  drivers/gpu/drm/i915/soc/intel_dram.c | 4 ++++
> >  drivers/gpu/drm/i915/soc/intel_dram.h | 1 +
> >  3 files changed, 6 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index 354ef75ef6a5..5bf3b4ab2baa 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -1233,6 +1233,7 @@
> >  #define   OROM_OFFSET_MASK			REG_GENMASK(20, 16)
> >  
> >  #define MTL_MEM_SS_INFO_GLOBAL			_MMIO(0x45700)
> > +#define   XE3P_ECC_IMPACTING_DE			REG_BIT(12)
> >  #define   MTL_N_OF_ENABLED_QGV_POINTS_MASK	REG_GENMASK(11, 8)
> >  #define   MTL_N_OF_POPULATED_CH_MASK		REG_GENMASK(7, 4)
> >  #define   MTL_DDR_TYPE_MASK			REG_GENMASK(3, 0)
> > diff --git a/drivers/gpu/drm/i915/soc/intel_dram.c b/drivers/gpu/drm/i915/soc/intel_dram.c
> > index 8841cfe1cac8..bf9f8e38d6ba 100644
> > --- a/drivers/gpu/drm/i915/soc/intel_dram.c
> > +++ b/drivers/gpu/drm/i915/soc/intel_dram.c
> > @@ -685,6 +685,7 @@ static int gen12_get_dram_info(struct drm_i915_private *i915, struct dram_info *
> >  
> >  static int xelpdp_get_dram_info(struct drm_i915_private *i915, struct dram_info *dram_info)
> >  {
> > +	struct intel_display *display = i915->display;
> >  	u32 val = intel_uncore_read(&i915->uncore, MTL_MEM_SS_INFO_GLOBAL);
> >  
> >  	switch (REG_FIELD_GET(MTL_DDR_TYPE_MASK, val)) {
> > @@ -723,6 +724,9 @@ static int xelpdp_get_dram_info(struct drm_i915_private *i915, struct dram_info
> >  	dram_info->num_qgv_points = REG_FIELD_GET(MTL_N_OF_ENABLED_QGV_POINTS_MASK, val);
> >  	/* PSF GV points not supported in D14+ */
> >  
> > +	if (DISPLAY_VER(display) >= 35)
> > +		dram_info->ecc_impacting_de = REG_FIELD_GET(XE3P_ECC_IMPACTING_DE, val);
> > +
> >  	return 0;
> >  }
> >  
> > diff --git a/drivers/gpu/drm/i915/soc/intel_dram.h b/drivers/gpu/drm/i915/soc/intel_dram.h
> > index 03a973f1c941..ac77f1ab409f 100644
> > --- a/drivers/gpu/drm/i915/soc/intel_dram.h
> > +++ b/drivers/gpu/drm/i915/soc/intel_dram.h
> > @@ -30,6 +30,7 @@ struct dram_info {
> >  	u8 num_channels;
> >  	u8 num_qgv_points;
> >  	u8 num_psf_gv_points;
> > +	bool ecc_impacting_de; /* Only valid from Xe3p_LPD onward. */
> >  	bool symmetric_memory;
> >  	bool has_16gb_dimms;
> >  };
> 
> -- 
> Jani Nikula, Intel