linux-kernel - Re: [PATCH drm-misc-next v2 5/7] drm/gpuvm: add an abstraction for a VM / BO combination

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Message-ID: <20230907130528.5ec58bfd@collabora.com>
Date:   Thu, 7 Sep 2023 13:05:28 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Danilo Krummrich <dakr@...hat.com>
Cc:     airlied@...il.com, daniel@...ll.ch, matthew.brost@...el.com,
        thomas.hellstrom@...ux.intel.com, sarah.walker@...tec.com,
        donald.robson@...tec.com, christian.koenig@....com,
        faith.ekstrand@...labora.com, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v2 5/7] drm/gpuvm: add an abstraction for
 a VM / BO combination

On Thu, 7 Sep 2023 11:41:11 +0200
Danilo Krummrich <dakr@...hat.com> wrote:

> On 9/7/23 10:42, Boris Brezillon wrote:
> > On Wed,  6 Sep 2023 23:47:13 +0200
> > Danilo Krummrich <dakr@...hat.com> wrote:
> >   
> >> +void drm_gpuvm_bo_destroy(struct kref *kref);  
> > 
> > I usually keep kref's release functions private so people are not
> > tempted to use them.  
> 
> I think I did that because drm_gpuvm_bo_put() needs it.

Yeah, but you can move the drm_gpuvm_bo_put() implementation to the C
file and make this one private.

> 
> >   
> >> +
> >> +/**
> >> + * drm_gpuvm_bo_get() - acquire a struct drm_gpuvm_bo reference
> >> + * @vm_bo: the &drm_gpuvm_bo to acquire the reference of
> >> + *
> >> + * This function acquires an additional reference to @vm_bo. It is illegal to
> >> + * call this without already holding a reference. No locks required.
> >> + */
> >> +static inline struct drm_gpuvm_bo *
> >> +drm_gpuvm_bo_get(struct drm_gpuvm_bo *vm_bo)
> >> +{
> >> +	kref_get(&vm_bo->kref);
> >> +	return vm_bo;
> >> +}
> >> +
> >> +/**
> >> + * drm_gpuvm_bo_put() - drop a struct drm_gpuvm_bo reference
> >> + * @vm_bo: the &drm_gpuvm_bo to release the reference of
> >> + *
> >> + * This releases a reference to @vm_bo.
> >> + */
> >> +static inline void
> >> +drm_gpuvm_bo_put(struct drm_gpuvm_bo *vm_bo)
> >> +{
> >> +	kref_put(&vm_bo->kref, drm_gpuvm_bo_destroy);  
> > 
> > nit: can we have
> > 
> > 	if (vm_bo)
> > 		kref_put(&vm_bo->kref, drm_gpuvm_bo_destroy);
> > 
> > so we don't have to bother testing the vm_bo value in the error/cleanup
> > paths?
> >   
> >> +}
> >> +  
> >   
>