linux-kernel - Re: [PATCH v3 2/7] drm/msm: adreno: add plumbing to generate bandwidth vote table for GMU

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Message-ID: <0dabac7a-bc7e-4075-86ed-3d4c25908ffb@oss.qualcomm.com>
Date: Fri, 29 Nov 2024 16:21:40 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Neil Armstrong <neil.armstrong@...aro.org>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 2/7] drm/msm: adreno: add plumbing to generate
 bandwidth vote table for GMU

On 28.11.2024 11:25 AM, Neil Armstrong wrote:
> The Adreno GPU Management Unit (GMU) can also scale DDR Bandwidth along
> the Frequency and Power Domain level, but by default we leave the
> OPP core scale the interconnect ddr path.
> 
> While scaling via the interconnect path was sufficient, newer GPUs
> like the A750 requires specific vote paremeters and bandwidth to
> achieve full functionality.
> 
> In order to calculate vote values used by the GPU Management
> Unit (GMU), we need to parse all the possible OPP Bandwidths and
> create a vote value to be sent to the appropriate Bus Control
> Modules (BCMs) declared in the GPU info struct.
> 
> This vote value is called IB, while on the othe side the GMU also
> takes another vote called AB which is a 16bit quantized value
> of the bandwidth against the maximum supported bandwidth.
> 
> The vote array will then be used to dynamically generate the GMU
> bw_table sent during the GMU power-up.
> 
> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.c | 174 ++++++++++++++++++++++++++++++++++
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  14 +++
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.h |   1 +
>  drivers/gpu/drm/msm/adreno/a6xx_hfi.h |   5 +
>  4 files changed, 194 insertions(+)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> index 14db7376c712d19446b38152e480bd5a1e0a5198..ee2010a01186721dd377f1655fcf05ddaff77131 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.c
> @@ -9,6 +9,7 @@
>  #include <linux/pm_domain.h>
>  #include <linux/pm_opp.h>
>  #include <soc/qcom/cmd-db.h>
> +#include <soc/qcom/tcs.h>
>  #include <drm/drm_gem.h>
>  
>  #include "a6xx_gpu.h"
> @@ -1287,6 +1288,131 @@ static int a6xx_gmu_memory_probe(struct a6xx_gmu *gmu)
>  	return 0;
>  }
>  
> +/**
> + * struct bcm_db - Auxiliary data pertaining to each Bus Clock Manager (BCM)
> + * @unit: divisor used to convert bytes/sec bw value to an RPMh msg
> + * @width: multiplier used to convert bytes/sec bw value to an RPMh msg
> + * @vcd: virtual clock domain that this bcm belongs to
> + * @reserved: reserved field
> + */
> +struct bcm_db {
> +	__le32 unit;
> +	__le16 width;
> +	u8 vcd;
> +	u8 reserved;
> +};
> +
> +static u64 bcm_div(u64 num, u32 base)
> +{
> +	/* Ensure that small votes aren't lost. */
> +	if (num && num < base)
> +		return 1;
> +
> +	do_div(num, base);
> +
> +	return num;
> +}

This should live in include/soc/qcom/bcm.h, similarly to tcs.h in
that directory

> +static int a6xx_gmu_rpmh_bw_votes_init(const struct a6xx_info *info,
> +				       struct a6xx_gmu *gmu)
> +{
> +	const struct bcm_db *bcm_data[GMU_MAX_BCMS] = { 0 };
> +	unsigned int bcm_index, bw_index, bcm_count = 0;
> +
> +	if (!info->bcms)
> +		return 0;
> +
> +	/* Retrieve BCM data from cmd-db */
> +	for (bcm_index = 0; bcm_index < GMU_MAX_BCMS; bcm_index++) {
> +		size_t count;
> +
> +		/* Stop at first unconfigured bcm */
> +		if (!info->bcms[bcm_index].name)
> +			break;
> +
> +		bcm_data[bcm_index] = cmd_db_read_aux_data(
> +						info->bcms[bcm_index].name,
> +						&count);
> +		if (IS_ERR(bcm_data[bcm_index]))
> +			return PTR_ERR(bcm_data[bcm_index]);
> +
> +		if (!count)
> +			return -EINVAL;
> +
> +		++bcm_count;
> +	}
> +
> +	/* Generate BCM votes values for each bandwidth & BCM */
> +	for (bw_index = 0; bw_index < gmu->nr_gpu_bws; bw_index++) {
> +		u32 *data = gmu->gpu_ib_votes[bw_index];
> +		u32 bw = gmu->gpu_bw_table[bw_index];
> +
> +		/* Calculations loosely copied from bcm_aggregate() & tcs_cmd_gen() */

Ditto, perhaps this should be exported from icc

[...]

Konrad