Re: [PATCH 7/8] drm/amdgpu: reserve vram for memory training

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Here is where you definitively set "ret" so DO NOT preinitialize it to 0,
just to avoid "pesky compiler unininitialized variable warnings"--those
are helpful to make the code more secure: a variable should be intentionally
initialized in all paths.

Rico: Still in confusion, pre-initialization can avoid "uninitialized variable", why should we can't pre-initialize?

From: Tuikov, Luben <Luben.Tuikov@xxxxxxx>
Sent: Wednesday, October 9, 2019 11:44
To: Alex Deucher <alexdeucher@xxxxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx <amd-gfx@xxxxxxxxxxxxxxxxxxxxx>
Cc: Deucher, Alexander <Alexander.Deucher@xxxxxxx>; Yin, Tianci (Rico) <Tianci.Yin@xxxxxxx>
Subject: Re: [PATCH 7/8] drm/amdgpu: reserve vram for memory training
 
On 2019-10-08 3:29 p.m., Alex Deucher wrote:
> From: "Tianci.Yin" <tianci.yin@xxxxxxx>
>
> memory training using specific fixed vram segment, reserve these
> segments before anyone may allocate it.
>
> Change-Id: I1436755813a565608a2857a683f535377620a637
> Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx>
> Signed-off-by: Tianci.Yin <tianci.yin@xxxxxxx>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 96 +++++++++++++++++++++++++
>  1 file changed, 96 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index 74a9bd94f10c..0819721af16e 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -1667,6 +1667,93 @@ static int amdgpu_ttm_fw_reserve_vram_init(struct amdgpu_device *adev)
>                                          &adev->fw_vram_usage.va);
>  }

> +/*
> + * Memoy training reservation functions
> + */

Include an empty line between the two comments, just as you would
a paragraph in written text.

> +/**
> + * amdgpu_ttm_training_reserve_vram_fini - free memory training reserved vram
> + *
> + * @adev: amdgpu_device pointer
> + *
> + * free memory training reserved vram if it has been reserved.
> + */
> +static int amdgpu_ttm_training_reserve_vram_fini(struct amdgpu_device *adev)
> +{
> +     int ret = 0;
> +     struct psp_memory_training_context *ctx = &adev->psp.mem_train_ctx;
> +
> +     ctx->init = PSP_MEM_TRAIN_NOT_SUPPORT;
> +     if(ctx->c2p_bo) {

Space after keywords, according to LKCS:
if (...)

> +             amdgpu_bo_free_kernel(&ctx->c2p_bo, NULL, NULL);
> +             ctx->c2p_bo = NULL;
> +     }
> +     if(ctx->p2c_bo) {

Space after keywords, according to LKCS:
if (...)

> +             amdgpu_bo_free_kernel(&ctx->p2c_bo, NULL, NULL);
> +             ctx->p2c_bo = NULL;
> +     }
> +
> +     return ret;
> +}

Get rid of "ret" variable altogether as it is not used in this function.

> +
> +/**
> + * amdgpu_ttm_training_reserve_vram_init - create bo vram reservation from memory training
> + *
> + * @adev: amdgpu_device pointer
> + *
> + * create bo vram reservation from memory training.
> + */
> +static int amdgpu_ttm_training_reserve_vram_init(struct amdgpu_device *adev)
> +{
> +     int ret = 0;

DO NOT preinitialize ret.

> +     struct psp_memory_training_context *ctx = &adev->psp.mem_train_ctx;
> +
> +     memset(ctx, 0, sizeof(*ctx));
> +     if(!adev->fw_vram_usage.mem_train_support) {

Space after keywords: "if (".

> +             DRM_DEBUG("memory training does not support!\n");
> +             return 0;
> +     }
> +
> +     ctx->c2p_train_data_offset = adev->fw_vram_usage.mem_train_fb_loc;
> +     ctx->p2c_train_data_offset = (adev->gmc.mc_vram_size - GDDR6_MEM_TRAINING_OFFSET);
> +     ctx->train_data_size = GDDR6_MEM_TRAINING_DATA_SIZE_IN_BYTES;
> +
> +     DRM_DEBUG("train_data_size:%llx,p2c_train_data_offset:%llx,c2p_train_data_offset:%llx.\n",
> +               ctx->train_data_size,
> +               ctx->p2c_train_data_offset,
> +               ctx->c2p_train_data_offset);
> +
> +     ret = amdgpu_bo_create_kernel_at(adev,

Here is where you definitively set "ret" so DO NOT preinitialize it to 0,
just to avoid "pesky compiler unininitialized variable warnings"--those
are helpful to make the code more secure: a variable should be intentionally
initialized in all paths.

> +                                      ctx->p2c_train_data_offset,
> +                                      ctx->train_data_size,
> +                                      AMDGPU_GEM_DOMAIN_VRAM,
> +                                      &ctx->p2c_bo,
> +                                      NULL);
> +     if(ret) {

Space after keywords "if (".

> +             DRM_ERROR("alloc p2c_bo failed(%d)!\n", ret);
> +             ret = -ENOMEM;
> +             goto err_out;
> +     }
> +
> +     ret = amdgpu_bo_create_kernel_at(adev,
> +                                      ctx->c2p_train_data_offset,
> +                                      ctx->train_data_size,
> +                                      AMDGPU_GEM_DOMAIN_VRAM,
> +                                      &ctx->c2p_bo,
> +                                      NULL);
> +     if(ret) {

Space after keywords: "if (", according to LKCS.

Regards,
Luben

> +             DRM_ERROR("alloc c2p_bo failed(%d)!\n", ret);
> +             ret = -ENOMEM;
> +             goto err_out;
> +     }
> +
> +     ctx->init = PSP_MEM_TRAIN_RESERVE_SUCCESS;
> +     return 0;
> +
> +err_out:
> +     amdgpu_ttm_training_reserve_vram_fini(adev);
> +     return ret;
> +}
> +
>  /**
>   * amdgpu_ttm_init - Init the memory management (ttm) as well as various
>   * gtt/vram related fields.
> @@ -1740,6 +1827,14 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
>                return r;
>        }

> +     /*
> +      *The reserved vram for memory training must be pinned to the specified
> +      *place on the VRAM, so reserve it early.
> +      */
> +     r = amdgpu_ttm_training_reserve_vram_init(adev);
> +     if (r)
> +             return r;
> +
>        /* allocate memory as required for VGA
>         * This is used for VGA emulation and pre-OS scanout buffers to
>         * avoid display artifacts while transitioning between pre-OS
> @@ -1825,6 +1920,7 @@ void amdgpu_ttm_fini(struct amdgpu_device *adev)
>                return;

>        amdgpu_ttm_debugfs_fini(adev);
> +     amdgpu_ttm_training_reserve_vram_fini(adev);
>        amdgpu_ttm_fw_reserve_vram_fini(adev);
>        if (adev->mman.aper_base_kaddr)
>                iounmap(adev->mman.aper_base_kaddr);
>

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