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

["Christian König" <ckoenig.leichtzumerken-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Am 09.10.19 um 13:12 schrieb Yin, Tianci (Rico):
> 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?

Because it avoids the uninitialized variable warning :)

See we really want the warning because it means that we have a bug in 
the code somewhere.

Regards,
Christian.

> ------------------------------------------------------------------------
> *From:* Tuikov, Luben <Luben.Tuikov-5C7GfCeVMHo@public.gmane.org>
> *Sent:* Wednesday, October 9, 2019 11:44
> *To:* Alex Deucher <alexdeucher-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>; 
> amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org <amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>
> *Cc:* Deucher, Alexander <Alexander.Deucher-5C7GfCeVMHo@public.gmane.org>; Yin, Tianci 
> (Rico) <Tianci.Yin-5C7GfCeVMHo@public.gmane.org>
> *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-5C7GfCeVMHo@public.gmane.org>
> >
> > memory training using specific fixed vram segment, reserve these
> > segments before anyone may allocate it.
> >
> > Change-Id: I1436755813a565608a2857a683f535377620a637
> > Reviewed-by: Alex Deucher <alexander.deucher-5C7GfCeVMHo@public.gmane.org>
> > Signed-off-by: Tianci.Yin <tianci.yin-5C7GfCeVMHo@public.gmane.org>
> > ---
> >  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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