linux-kernel - Re: [PATCH 3/4] drm/msm/a6xx: Get HBB dynamically, if available

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Message-ID: <CACu1E7GMf0Mx2ZX_t76h+b1CPin49LGix7c5uvoWaJZC3dKyOw@mail.gmail.com>
Date: Wed, 9 Apr 2025 11:12:31 -0400
From: Connor Abbott <cwabbott0@...il.com>
To: Konrad Dybcio <konradybcio@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, 
	Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Dmitry Baryshkov <lumag@...nel.org>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-hardening@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, 
	Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH 3/4] drm/msm/a6xx: Get HBB dynamically, if available

On Wed, Apr 9, 2025 at 10:48 AM Konrad Dybcio <konradybcio@...nel.org> wrote:
>
> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>
> The Highest Bank address Bit value can change based on memory type used.
>
> Attempt to retrieve it dynamically, and fall back to a reasonable
> default (the one used prior to this change) on error.
>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 22 ++++++++++++++++------
>  1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 06465bc2d0b4b128cddfcfcaf1fe4252632b6777..0cc397378c99db35315209d0265ad9223e8b55c7 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -13,6 +13,7 @@
>  #include <linux/firmware/qcom/qcom_scm.h>
>  #include <linux/pm_domain.h>
>  #include <linux/soc/qcom/llcc-qcom.h>
> +#include <linux/soc/qcom/smem.h>
>
>  #define GPU_PAS_ID 13
>
> @@ -669,17 +670,22 @@ static void a6xx_calc_ubwc_config(struct adreno_gpu *gpu)
>  static void a6xx_set_ubwc_config(struct msm_gpu *gpu)
>  {
>         struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
> +       u32 hbb = qcom_smem_dram_get_hbb();
> +       u32 ubwc_mode = adreno_gpu->ubwc_config.ubwc_swizzle & 1;
> +       u32 level2_swizzling_dis = !(adreno_gpu->ubwc_config.ubwc_swizzle & 2);
> +       u32 hbb_hi, hbb_lo;
> +
>         /*
>          * We subtract 13 from the highest bank bit (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.
>          */
> -       BUG_ON(adreno_gpu->ubwc_config.highest_bank_bit < 13);
> -       u32 hbb = adreno_gpu->ubwc_config.highest_bank_bit - 13;
> -       u32 hbb_hi = hbb >> 2;
> -       u32 hbb_lo = hbb & 3;
> -       u32 ubwc_mode = adreno_gpu->ubwc_config.ubwc_swizzle & 1;
> -       u32 level2_swizzling_dis = !(adreno_gpu->ubwc_config.ubwc_swizzle & 2);
> +       if (hbb < 0)
> +               hbb = adreno_gpu->ubwc_config.highest_bank_bit;

No. The value we expose to userspace must match what we program.
You'll break VK_EXT_host_image_copy otherwise.

Connor

> +       hbb -= 13;
> +       BUG_ON(hbb < 0);
> +       hbb_hi = hbb >> 2;
> +       hbb_lo = hbb & 3;
>
>         gpu_write(gpu, REG_A6XX_RB_NC_MODE_CNTL,
>                   level2_swizzling_dis << 12 |
> @@ -2467,6 +2473,10 @@ struct msm_gpu *a6xx_gpu_init(struct drm_device *dev)
>         bool is_a7xx;
>         int ret;
>
> +       /* We need data from SMEM to retrieve HBB in set_ubwc_config() */
> +       if (!qcom_smem_is_available())
> +               return ERR_PTR(-EPROBE_DEFER);
> +
>         a6xx_gpu = kzalloc(sizeof(*a6xx_gpu), GFP_KERNEL);
>         if (!a6xx_gpu)
>                 return ERR_PTR(-ENOMEM);
>
> --
> 2.49.0
>