Re: [PATCH v3 2/5] drm/i915/bw: Extract platform-specific parameters

[Gustavo Sousa <gustavo.sousa@intel.com>]

Jani Nikula <jani.nikula@intel.com> writes:

> On Fri, 15 May 2026, Gustavo Sousa <gustavo.sousa@intel.com> wrote:
>> Gustavo Sousa <gustavo.sousa@intel.com> writes:
>>
>>> We got confirmation from the hardware team that the bandwidth parameters
>>> deprogbwlimit and derating are platform-specific and not tied to the
>>> display IP.  As such, let's make sure that we use platform checks for
>>> those.
>>>
>>> The rest of the members of struct intel_sa_info are tied to the display
>>> IP and we will deal with them as a follow-up.
>>>
>>> v2:
>>>   - Use good old if-ladder instead of weird-looking pattern "assign ret,
>>>     check platform, then return ret". (Jani, Matt)
>>>   - Have a single call site for get_platform_bw_params() and pass the
>>>     result as parameter to the *_get_bw_info() functions. (Jani)
>>>   - Avoid using "plat" as abbreviation for "platform". (Jani)
>>>   - s/_plat_bw_params/_bw_params/, since all of the instances are
>>>     prefixed with platform names. (Jani)
>>>   - s/struct intel_platform_bw_params/struct intel_soc_bw_params/.
>>>     (Matt)
>>>   - Do not return a default value; prefer to return NULL and
>>>     intentionally cause a NULL pointer dereference if a platform is
>>>     missing. (Gustavo)
>>>
>>> v3:
>>>   - Call get_soc_bw_params() only after the check on
>>>     HAS_DISPLAY(display). (Jani)
>>>   - Combine if-ladder branches for adl_s_bw_params into a single one.
>>>     (Matt)
>>>   - Flatten if-ladder by checking for WCL before PTL (as opposed to
>>>     checking for WCL inside the brace for PTL). (Matt)
>>>   - Bail out of intel_bw_init_hw() if display version is below 11.
>>>     (Gustavo)
>>>
>>> Cc: Jani Nikula <jani.nikula@intel.com>
>>> Cc: Matt Roper <matthew.d.roper@intel.com>
>>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>>> Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
>>> ---
>>>  drivers/gpu/drm/i915/display/intel_bw.c | 162 ++++++++++++++++++++++----------
>>>  1 file changed, 114 insertions(+), 48 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
>>> index 7eef693b51ad..351ecf741b54 100644
>>> --- a/drivers/gpu/drm/i915/display/intel_bw.c
>>> +++ b/drivers/gpu/drm/i915/display/intel_bw.c
>>> @@ -372,81 +372,144 @@ static int icl_sagv_max_dclk(const struct intel_qgv_info *qi)
>>>  	return dclk;
>>>  }
>>>  
>>> +struct intel_soc_bw_params {
>>> +	u8 deprogbwlimit;
>>> +	u8 derating;
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params icl_bw_params = {
>>> +	.deprogbwlimit = 25,
>>> +	.derating = 10,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params tgl_bw_params = {
>>> +	.deprogbwlimit = 34,
>>> +	.derating = 10,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params rkl_bw_params = {
>>> +	.deprogbwlimit = 20,
>>> +	.derating = 10,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params adl_s_bw_params = {
>>> +	.deprogbwlimit = 38,
>>> +	.derating = 10,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params adl_p_bw_params = {
>>> +	.deprogbwlimit = 38,
>>> +	.derating = 20,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params bmg_bw_params = {
>>> +	.deprogbwlimit = 53,
>>> +	.derating = 30,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params bmg_ecc_bw_params = {
>>> +	.deprogbwlimit = 53,
>>> +	.derating = 45,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params ptl_bw_params = {
>>> +	.deprogbwlimit = 65,
>>> +	.derating = 10,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params wcl_bw_params = {
>>> +	.deprogbwlimit = 22,
>>> +	.derating = 10,
>>> +};
>>> +
>>> +static const struct intel_soc_bw_params *get_soc_bw_params(struct intel_display *display)
>>> +{
>>> +	if (display->platform.dgfx) {
>>> +		if (display->platform.dg1) {
>>> +			return &tgl_bw_params;
>>> +		} else if (display->platform.battlemage) {
>>> +			const struct dram_info *dram_info = intel_dram_info(display);
>>> +
>>> +			if (dram_info->type == INTEL_DRAM_GDDR_ECC)
>>> +				return &bmg_ecc_bw_params;
>>> +			else
>>> +				return &bmg_bw_params;
>>> +		}
>>> +	} else {
>>> +		if (display->platform.icelake ||
>>> +		    display->platform.jasperlake ||
>>> +		    display->platform.elkhartlake)
>>> +			return &icl_bw_params;
>>> +		else if (display->platform.tigerlake)
>>> +			return &tgl_bw_params;
>>> +		else if (display->platform.rocketlake)
>>> +			return &rkl_bw_params;
>>> +		else if (display->platform.alderlake_s ||
>>> +			 display->platform.meteorlake ||
>>> +			 display->platform.lunarlake)
>>> +			return &adl_s_bw_params;
>>> +		else if (display->platform.alderlake_p)
>>> +			return &adl_p_bw_params;
>>> +		else if (display->platform.pantherlake_wildcatlake)
>>> +			return &wcl_bw_params;
>>> +		else if (display->platform.pantherlake ||
>>> +			 display->platform.novalake)
>>> +			return &ptl_bw_params;
>>> +	}
>>> +
>>> +	drm_WARN(display->drm, 1, "Platform-specific bandwidth parameters not found!\n");
>>
>> CI shows the warning because DG2 does not use bandwidth
>> parameters and get_soc_bw_params() rightfully does not cover DG2.
>>
>> We could just get rid of the warnings in get_soc_bw_params() and
>> get_display_bw_params() all together.  The idea of the warning was to
>> serve as an aid to the developer, but I guess tracing the null pointer
>> dereference back to those functions shouldn't be too hard?
>>
>> Another idea is to make sure that only the functions that use those
>> parameters make the call to get_{soc,display}_bw_params().
>>
>> Jani, I know you preferred the other way around, but maybe this is a
>> compelling reason for moving the call to the direct users?
>
> I still prefer figuring the pointer out early, and passing it around to
> the places that need it. Actually, ditto for dram_info above. I

Ack.

> refactored this stuff once to call intel_dram_info() once, and pass the
> pointer around.
>
> I think the alternatives are:
>
> - Remove the drm_WARN() altogether.

Okay.  I think I'll just take the easy way out by dropping them in the
next iteration.

--
Gustavo Sousa

>
> - Return NULL directly for platforms where the parameters don't make
>   sense, e.g. DG2.
>
> BR,
> Jani.
>
>>
>> --
>> Gustavo Sousa
>>
>>> +
>>> +	return NULL;
>>> +}
>>> +
>>>  struct intel_sa_info {
>>>  	u16 displayrtids;
>>> -	u8 deburst, deprogbwlimit, derating;
>>> +	u8 deburst;
>>>  };
>>>  
>>>  static const struct intel_sa_info icl_sa_info = {
>>>  	.deburst = 8,
>>> -	.deprogbwlimit = 25, /* GB/s */
>>>  	.displayrtids = 128,
>>> -	.derating = 10,
>>>  };
>>>  
>>>  static const struct intel_sa_info tgl_sa_info = {
>>>  	.deburst = 16,
>>> -	.deprogbwlimit = 34, /* GB/s */
>>>  	.displayrtids = 256,
>>> -	.derating = 10,
>>>  };
>>>  
>>>  static const struct intel_sa_info rkl_sa_info = {
>>>  	.deburst = 8,
>>> -	.deprogbwlimit = 20, /* GB/s */
>>>  	.displayrtids = 128,
>>> -	.derating = 10,
>>>  };
>>>  
>>>  static const struct intel_sa_info adls_sa_info = {
>>>  	.deburst = 16,
>>> -	.deprogbwlimit = 38, /* GB/s */
>>>  	.displayrtids = 256,
>>> -	.derating = 10,
>>>  };
>>>  
>>>  static const struct intel_sa_info adlp_sa_info = {
>>>  	.deburst = 16,
>>> -	.deprogbwlimit = 38, /* GB/s */
>>>  	.displayrtids = 256,
>>> -	.derating = 20,
>>>  };
>>>  
>>>  static const struct intel_sa_info mtl_sa_info = {
>>>  	.deburst = 32,
>>> -	.deprogbwlimit = 38, /* GB/s */
>>>  	.displayrtids = 256,
>>> -	.derating = 10,
>>> -};
>>> -
>>> -static const struct intel_sa_info xe2_hpd_sa_info = {
>>> -	.derating = 30,
>>> -	.deprogbwlimit = 53,
>>> -	/* Other values not used by simplified algorithm */
>>> -};
>>> -
>>> -static const struct intel_sa_info xe2_hpd_ecc_sa_info = {
>>> -	.derating = 45,
>>> -	.deprogbwlimit = 53,
>>> -	/* Other values not used by simplified algorithm */
>>>  };
>>>  
>>>  static const struct intel_sa_info xe3lpd_sa_info = {
>>>  	.deburst = 32,
>>> -	.deprogbwlimit = 65, /* GB/s */
>>>  	.displayrtids = 256,
>>> -	.derating = 10,
>>>  };
>>>  
>>>  static const struct intel_sa_info xe3lpd_3002_sa_info = {
>>>  	.deburst = 32,
>>> -	.deprogbwlimit = 22, /* GB/s */
>>>  	.displayrtids = 256,
>>> -	.derating = 10,
>>>  };
>>>  
>>>  static int icl_get_bw_info(struct intel_display *display,
>>>  			   const struct dram_info *dram_info,
>>> +			   const struct intel_soc_bw_params *soc_bw_params,
>>>  			   const struct intel_sa_info *sa)
>>>  {
>>>  	struct intel_qgv_info qi = {};
>>> @@ -466,7 +529,7 @@ static int icl_get_bw_info(struct intel_display *display,
>>>  	}
>>>  
>>>  	dclk_max = icl_sagv_max_dclk(&qi);
>>> -	maxdebw = min(sa->deprogbwlimit * 1000, dclk_max * 16 * 6 / 10);
>>> +	maxdebw = min(soc_bw_params->deprogbwlimit * 1000, dclk_max * 16 * 6 / 10);
>>>  	ipqdepth = min(ipqdepthpch, sa->displayrtids / num_channels);
>>>  	qi.deinterleave = DIV_ROUND_UP(num_channels, is_y_tile ? 4 : 2);
>>>  
>>> @@ -496,7 +559,7 @@ static int icl_get_bw_info(struct intel_display *display,
>>>  			bw = DIV_ROUND_UP(sp->dclk * clpchgroup * 32 * num_channels, ct);
>>>  
>>>  			bi->deratedbw[j] = min(maxdebw,
>>> -					       bw * (100 - sa->derating) / 100);
>>> +					       bw * (100 - soc_bw_params->derating) / 100);
>>>  
>>>  			drm_dbg_kms(display->drm,
>>>  				    "BW%d / QGV %d: num_planes=%d deratedbw=%u\n",
>>> @@ -518,6 +581,7 @@ static int icl_get_bw_info(struct intel_display *display,
>>>  
>>>  static int tgl_get_bw_info(struct intel_display *display,
>>>  			   const struct dram_info *dram_info,
>>> +			   const struct intel_soc_bw_params *soc_bw_params,
>>>  			   const struct intel_sa_info *sa)
>>>  {
>>>  	struct intel_qgv_info qi = {};
>>> @@ -554,7 +618,7 @@ static int tgl_get_bw_info(struct intel_display *display,
>>>  	dclk_max = icl_sagv_max_dclk(&qi);
>>>  
>>>  	peakbw = num_channels * DIV_ROUND_UP(qi.channel_width, 8) * dclk_max;
>>> -	maxdebw = min(sa->deprogbwlimit * 1000, peakbw * DEPROGBWPCLIMIT / 100);
>>> +	maxdebw = min(soc_bw_params->deprogbwlimit * 1000, peakbw * DEPROGBWPCLIMIT / 100);
>>>  
>>>  	ipqdepth = min(ipqdepthpch, sa->displayrtids / num_channels);
>>>  	/*
>>> @@ -599,7 +663,7 @@ static int tgl_get_bw_info(struct intel_display *display,
>>>  			bw = DIV_ROUND_UP(sp->dclk * clpchgroup * 32 * num_channels, ct);
>>>  
>>>  			bi->deratedbw[j] = min(maxdebw,
>>> -					       bw * (100 - sa->derating) / 100);
>>> +					       bw * (100 - soc_bw_params->derating) / 100);
>>>  			bi->peakbw[j] = DIV_ROUND_CLOSEST(sp->dclk *
>>>  							  num_channels *
>>>  							  qi.channel_width, 8);
>>> @@ -661,7 +725,7 @@ static void dg2_get_bw_info(struct intel_display *display)
>>>  
>>>  static int xe2_hpd_get_bw_info(struct intel_display *display,
>>>  			       const struct dram_info *dram_info,
>>> -			       const struct intel_sa_info *sa)
>>> +			       const struct intel_soc_bw_params *soc_bw_params)
>>>  {
>>>  	struct intel_qgv_info qi = {};
>>>  	int num_channels = dram_info->num_channels;
>>> @@ -676,14 +740,14 @@ static int xe2_hpd_get_bw_info(struct intel_display *display,
>>>  	}
>>>  
>>>  	peakbw = num_channels * qi.channel_width / 8 * icl_sagv_max_dclk(&qi);
>>> -	maxdebw = min(sa->deprogbwlimit * 1000, peakbw * DEPROGBWPCLIMIT / 10);
>>> +	maxdebw = min(soc_bw_params->deprogbwlimit * 1000, peakbw * DEPROGBWPCLIMIT / 10);
>>>  
>>>  	for (i = 0; i < qi.num_points; i++) {
>>>  		const struct intel_qgv_point *point = &qi.points[i];
>>>  		int bw = num_channels * (qi.channel_width / 8) * point->dclk;
>>>  
>>>  		display->bw.max[0].deratedbw[i] =
>>> -			min(maxdebw, (100 - sa->derating) * bw / 100);
>>> +			min(maxdebw, (100 - soc_bw_params->derating) * bw / 100);
>>>  		display->bw.max[0].peakbw[i] = bw;
>>>  
>>>  		drm_dbg_kms(display->drm, "QGV %d: deratedbw=%u peakbw: %u\n",
>>> @@ -792,11 +856,16 @@ static unsigned int icl_qgv_bw(struct intel_display *display,
>>>  void intel_bw_init_hw(struct intel_display *display)
>>>  {
>>>  	const struct dram_info *dram_info;
>>> +	const struct intel_soc_bw_params *soc_bw_params;
>>>  
>>>  	if (!HAS_DISPLAY(display))
>>>  		return;
>>>  
>>> +	if (DISPLAY_VER(display) < 11)
>>> +		return;
>>> +
>>>  	dram_info = intel_dram_info(display);
>>> +	soc_bw_params = get_soc_bw_params(display);
>>>  
>>>  	/*
>>>  	 * Starting with Xe3p_LPD, the hardware tells us whether memory has ECC
>>> @@ -809,28 +878,25 @@ void intel_bw_init_hw(struct intel_display *display)
>>>  
>>>  	if (DISPLAY_VER(display) >= 30) {
>>>  		if (DISPLAY_VERx100(display) == 3002)
>>> -			tgl_get_bw_info(display, dram_info, &xe3lpd_3002_sa_info);
>>> +			tgl_get_bw_info(display, dram_info, soc_bw_params, &xe3lpd_3002_sa_info);
>>>  		else
>>> -			tgl_get_bw_info(display, dram_info, &xe3lpd_sa_info);
>>> +			tgl_get_bw_info(display, dram_info, soc_bw_params, &xe3lpd_sa_info);
>>>  	} else if (DISPLAY_VERx100(display) >= 1401 && display->platform.dgfx) {
>>> -		if (dram_info->type == INTEL_DRAM_GDDR_ECC)
>>> -			xe2_hpd_get_bw_info(display, dram_info, &xe2_hpd_ecc_sa_info);
>>> -		else
>>> -			xe2_hpd_get_bw_info(display, dram_info, &xe2_hpd_sa_info);
>>> +		xe2_hpd_get_bw_info(display, dram_info, soc_bw_params);
>>>  	} else if (DISPLAY_VER(display) >= 14) {
>>> -		tgl_get_bw_info(display, dram_info, &mtl_sa_info);
>>> +		tgl_get_bw_info(display, dram_info, soc_bw_params, &mtl_sa_info);
>>>  	} else if (display->platform.dg2) {
>>>  		dg2_get_bw_info(display);
>>>  	} else if (display->platform.alderlake_p) {
>>> -		tgl_get_bw_info(display, dram_info, &adlp_sa_info);
>>> +		tgl_get_bw_info(display, dram_info, soc_bw_params, &adlp_sa_info);
>>>  	} else if (display->platform.alderlake_s) {
>>> -		tgl_get_bw_info(display, dram_info, &adls_sa_info);
>>> +		tgl_get_bw_info(display, dram_info, soc_bw_params, &adls_sa_info);
>>>  	} else if (display->platform.rocketlake) {
>>> -		tgl_get_bw_info(display, dram_info, &rkl_sa_info);
>>> +		tgl_get_bw_info(display, dram_info, soc_bw_params, &rkl_sa_info);
>>>  	} else if (DISPLAY_VER(display) == 12) {
>>> -		tgl_get_bw_info(display, dram_info, &tgl_sa_info);
>>> +		tgl_get_bw_info(display, dram_info, soc_bw_params, &tgl_sa_info);
>>>  	} else if (DISPLAY_VER(display) == 11) {
>>> -		icl_get_bw_info(display, dram_info, &icl_sa_info);
>>> +		icl_get_bw_info(display, dram_info, soc_bw_params, &icl_sa_info);
>>>  	}
>>>  }
>>>  
>>>
>>> -- 
>>> 2.53.0
>
> -- 
> Jani Nikula, Intel