linux-kernel - Re: [PATCH drm-misc-next 4/5] drm/gpuvm: fall back to drm_exec_lock

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Message-ID: <3c7b7683-da36-4ffe-a250-91eef019499f@redhat.com>
Date:   Sat, 25 Nov 2023 00:40:18 +0100
From:   Danilo Krummrich <dakr@...hat.com>
To:     Christian König <christian.koenig@....com>
Cc:     mripard@...nel.org, airlied@...il.com, daniel@...ll.ch,
        frank.binns@...tec.com, donald.robson@...tec.com,
        matt.coster@...tec.com, sarah.walker@...tec.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next 4/5] drm/gpuvm: fall back to
 drm_exec_lock_obj()

Hi Christian,

do you think it makes sense to handle this in drm_exec_prepare_obj() or
even dma_resv_reserve_fences() even?

- Danilo

On 11/25/23 00:36, Danilo Krummrich wrote:
> Fall back to drm_exec_lock_obj() if num_fences is zero for the
> drm_gpuvm_prepare_* function family.
> 
> Otherwise dma_resv_reserve_fences() would actually allocate slots even
> though num_fences is zero.
> 
> Cc: Christian König <christian.koenig@....com>
> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
> ---
>   drivers/gpu/drm/drm_gpuvm.c | 36 +++++++++++++++++++++++++++++++++---
>   include/drm/drm_gpuvm.h     | 23 +++--------------------
>   2 files changed, 36 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_gpuvm.c b/drivers/gpu/drm/drm_gpuvm.c
> index 54f5e8851de5..d1d1c2379e44 100644
> --- a/drivers/gpu/drm/drm_gpuvm.c
> +++ b/drivers/gpu/drm/drm_gpuvm.c
> @@ -1085,6 +1085,36 @@ drm_gpuvm_put(struct drm_gpuvm *gpuvm)
>   }
>   EXPORT_SYMBOL_GPL(drm_gpuvm_put);
>   
> +static int
> +exec_prepare_obj(struct drm_exec *exec, struct drm_gem_object *obj,
> +		 unsigned int num_fences)
> +{
> +	return num_fences ? drm_exec_prepare_obj(exec, obj, num_fences) :
> +			    drm_exec_lock_obj(exec, obj);
> +}
> +
> +/**
> + * drm_gpuvm_prepare_vm() - prepare the GPUVMs common dma-resv
> + * @gpuvm: the &drm_gpuvm
> + * @exec: the &drm_exec context
> + * @num_fences: the amount of &dma_fences to reserve
> + *
> + * Calls drm_exec_prepare_obj() for the GPUVMs dummy &drm_gem_object.
> + *
> + * Using this function directly, it is the drivers responsibility to call
> + * drm_exec_init() and drm_exec_fini() accordingly.
> + *
> + * Returns: 0 on success, negative error code on failure.
> + */
> +int
> +drm_gpuvm_prepare_vm(struct drm_gpuvm *gpuvm,
> +		     struct drm_exec *exec,
> +		     unsigned int num_fences)
> +{
> +	return exec_prepare_obj(exec, gpuvm->r_obj, num_fences);
> +}
> +EXPORT_SYMBOL_GPL(drm_gpuvm_prepare_vm);
> +
>   static int
>   __drm_gpuvm_prepare_objects(struct drm_gpuvm *gpuvm,
>   			    struct drm_exec *exec,
> @@ -1095,7 +1125,7 @@ __drm_gpuvm_prepare_objects(struct drm_gpuvm *gpuvm,
>   	int ret = 0;
>   
>   	for_each_vm_bo_in_list(gpuvm, extobj, &extobjs, vm_bo) {
> -		ret = drm_exec_prepare_obj(exec, vm_bo->obj, num_fences);
> +		ret = exec_prepare_obj(exec, vm_bo->obj, num_fences);
>   		if (ret)
>   			break;
>   	}
> @@ -1116,7 +1146,7 @@ drm_gpuvm_prepare_objects_locked(struct drm_gpuvm *gpuvm,
>   
>   	drm_gpuvm_resv_assert_held(gpuvm);
>   	list_for_each_entry(vm_bo, &gpuvm->extobj.list, list.entry.extobj) {
> -		ret = drm_exec_prepare_obj(exec, vm_bo->obj, num_fences);
> +		ret = exec_prepare_obj(exec, vm_bo->obj, num_fences);
>   		if (ret)
>   			break;
>   
> @@ -1186,7 +1216,7 @@ drm_gpuvm_prepare_range(struct drm_gpuvm *gpuvm, struct drm_exec *exec,
>   	drm_gpuvm_for_each_va_range(va, gpuvm, addr, end) {
>   		struct drm_gem_object *obj = va->gem.obj;
>   
> -		ret = drm_exec_prepare_obj(exec, obj, num_fences);
> +		ret = exec_prepare_obj(exec, obj, num_fences);
>   		if (ret)
>   			return ret;
>   	}
> diff --git a/include/drm/drm_gpuvm.h b/include/drm/drm_gpuvm.h
> index f94fec9a8517..b3f82ec7fb17 100644
> --- a/include/drm/drm_gpuvm.h
> +++ b/include/drm/drm_gpuvm.h
> @@ -544,26 +544,9 @@ struct drm_gpuvm_exec {
>   	} extra;
>   };
>   
> -/**
> - * drm_gpuvm_prepare_vm() - prepare the GPUVMs common dma-resv
> - * @gpuvm: the &drm_gpuvm
> - * @exec: the &drm_exec context
> - * @num_fences: the amount of &dma_fences to reserve
> - *
> - * Calls drm_exec_prepare_obj() for the GPUVMs dummy &drm_gem_object.
> - *
> - * Using this function directly, it is the drivers responsibility to call
> - * drm_exec_init() and drm_exec_fini() accordingly.
> - *
> - * Returns: 0 on success, negative error code on failure.
> - */
> -static inline int
> -drm_gpuvm_prepare_vm(struct drm_gpuvm *gpuvm,
> -		     struct drm_exec *exec,
> -		     unsigned int num_fences)
> -{
> -	return drm_exec_prepare_obj(exec, gpuvm->r_obj, num_fences);
> -}
> +int drm_gpuvm_prepare_vm(struct drm_gpuvm *gpuvm,
> +			 struct drm_exec *exec,
> +			 unsigned int num_fences);
>   
>   int drm_gpuvm_prepare_objects(struct drm_gpuvm *gpuvm,
>   			      struct drm_exec *exec,