linux-kernel - Re: [PATCH v3 04/15] drm/msm/a6xx: Extend and explain UBWC config

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Message-ID: <e19b5cd7-9125-a285-accc-ecf530804cfc@quicinc.com>
Date:   Wed, 1 Mar 2023 01:53:43 +0530
From:   Akhil P Oommen <quic_akhilpo@...cinc.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>
CC:     <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Rob Clark <robdclark@...omium.org>
Subject: Re: [PATCH v3 04/15] drm/msm/a6xx: Extend and explain UBWC config

On 2/23/2023 5:36 PM, Konrad Dybcio wrote:
> Rename lower_bit to hbb_lo and explain what it signifies.
> Add explanations (wherever possible to other tunables).
>
> Sort the variable definition and assignment alphabetically.
Sorting based on decreasing order of line length is more readable, isn't it?
>
> Port setting min_access_length, ubwc_mode and hbb_hi from downstream.
> Set default values for all of the tunables to zero, as they should be.
>
> Values were validated against downstream and will be fixed up in
> separate commits so as not to make this one even more messy.
>
> A618 remains untouched (left at hw defaults) in this patch.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 55 ++++++++++++++++++++++++++++-------
>  1 file changed, 45 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index c5f5d0bb3fdc..bdae341e0a7c 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -786,39 +786,74 @@ static void a6xx_set_cp_protect(struct msm_gpu *gpu)
>  static void a6xx_set_ubwc_config(struct msm_gpu *gpu)
>  {
>  	struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> -	u32 lower_bit = 2;
> +	/* Unknown, introduced with A640/680 */
>  	u32 amsbc = 0;
> +	/*
> +	 * The Highest Bank Bit value represents the bit of the highest DDR bank.
> +	 * We then subtract 13 from it (13 is the minimum value allowed by hw) and
> +	 * write the lowest two bits of the remaining value as hbb_lo and the
> +	 * one above it as hbb_hi to the hardware. The default values (when HBB is
> +	 * not specified) are 0, 0.
> +	 */
> +	u32 hbb_hi = 0;
> +	u32 hbb_lo = 0;
> +	/* Whether the minimum access length is 64 bits */
> +	u32 min_acc_len = 0;
> +	/* Unknown, introduced with A650 family, related to UBWC mode/ver 4 */
>  	u32 rgb565_predicator = 0;
> +	/* Unknown, introduced with A650 family */
>  	u32 uavflagprd_inv = 0;
> +	/* Entirely magic, per-GPU-gen value */
> +	u32 ubwc_mode = 0;
>  
>  	/* a618 is using the hw default values */
>  	if (adreno_is_a618(adreno_gpu))
>  		return;
>  
> -	if (adreno_is_a640_family(adreno_gpu))
> +	if (adreno_is_a619(adreno_gpu)) {
> +		/* HBB = 14 */
> +		hbb_lo = 1;
> +	}
> +
> +	if (adreno_is_a630(adreno_gpu)) {
> +		/* HBB = 15 */
> +		hbb_lo = 2;
> +	}
> +
> +	if (adreno_is_a640_family(adreno_gpu)) {
>  		amsbc = 1;
> +		/* HBB = 15 */
> +		hbb_lo = 2;
> +	}
>  
>  	if (adreno_is_a650(adreno_gpu) || adreno_is_a660(adreno_gpu)) {
> -		/* TODO: get ddr type from bootloader and use 2 for LPDDR4 */
> -		lower_bit = 3;
>  		amsbc = 1;
> +		/* TODO: get ddr type from bootloader and use 2 for LPDDR4 */
> +		/* HBB = 16 */
> +		hbb_lo = 3;
>  		rgb565_predicator = 1;
>  		uavflagprd_inv = 2;
>  	}
>  
>  	if (adreno_is_7c3(adreno_gpu)) {
> -		lower_bit = 1;
>  		amsbc = 1;
> +		/* HBB is unset in downstream DTS, defaulting to 0 */
This is incorrect. For 7c3 hbb value is 14. So hbb_lo should be 1. FYI, hbb configurations were moved to the driver from DT in recent downstream kernels.

-Akhil.
>  		rgb565_predicator = 1;
>  		uavflagprd_inv = 2;
>  	}
>  
>  	gpu_write(gpu, REG_A6XX_RB_NC_MODE_CNTL,
> -		rgb565_predicator << 11 | amsbc << 4 | lower_bit << 1);
> -	gpu_write(gpu, REG_A6XX_TPL1_NC_MODE_CNTL, lower_bit << 1);
> -	gpu_write(gpu, REG_A6XX_SP_NC_MODE_CNTL,
> -		uavflagprd_inv << 4 | lower_bit << 1);
> -	gpu_write(gpu, REG_A6XX_UCHE_MODE_CNTL, lower_bit << 21);
> +		  rgb565_predicator << 11 | hbb_hi << 10 | amsbc << 4 |
> +		  min_acc_len << 3 | hbb_lo << 1 | ubwc_mode);
> +
> +	gpu_write(gpu, REG_A6XX_TPL1_NC_MODE_CNTL, hbb_hi << 4 |
> +		  min_acc_len << 3 | hbb_lo << 1 | ubwc_mode);
> +
> +	gpu_write(gpu, REG_A6XX_SP_NC_MODE_CNTL, hbb_hi << 10 |
> +		  uavflagprd_inv << 4 | min_acc_len << 3 |
> +		  hbb_lo << 1 | ubwc_mode);
> +
> +	gpu_write(gpu, REG_A6XX_UCHE_MODE_CNTL, min_acc_len << 23 | hbb_lo << 21);
>  }
>  
>  static int a6xx_cp_init(struct msm_gpu *gpu)
>