Re: [PATCH v1 3/8] drm/etnaviv: Drop the second argument of the etnaviv_gem_new_impl()

[suijingfeng]

Hi,  Lucas


Thanks for you guidance!


On 2023/7/17 17:51, Lucas Stach wrote:
> Hi Jingfeng,
>
> Am Freitag, dem 23.06.2023 um 18:08 +0800 schrieb Sui Jingfeng:
> > From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> >
> > Because it is not used by the etnaviv_gem_new_impl() function,
> > no functional change.
> I think it would make sense to move into the opposite direction: in
> both callsites of etnaviv_gem_new_impl we immediately call
> drm_gem_object_init with the size.

Really?

But there are multiple call path to the etnaviv_gem_new_impl() function.


Code path 1 (PRIME):

|- etnaviv_gem_prime_import_sg_table()

|--  etnaviv_gem_new_private()

|--- etnaviv_gem_new_impl(dev, size, flags, ops, &obj)

|--- drm_gem_private_object_init(dev, obj, size)


Code path 2 (USERPTR):

|- etnaviv_gem_new_userptr()

|--  etnaviv_gem_new_private()

|--- etnaviv_gem_new_impl(dev, size, flags, ops, &obj)

|--- drm_gem_private_object_init(dev, obj, size)


Code path 3 (construct a GEM buffer object for the user-space):

|- etnaviv_ioctl_gem_new()

|-- etnaviv_gem_new_handle()

|--- etnaviv_gem_new_impl(dev, size, flags, &etnaviv_gem_shmem_ops, &obj);

|---  drm_gem_object_init(dev, obj, size);


If I understand this correctly:


Code path 1 is for cross device (and cross driver) buffer-sharing,

Code path 2 is going to share the buffer the userspace,


*Only* the code path 3 is to construct a GEM buffer object for the 
user-space the userspace,

that is say, *only* the code path 3 need to do the backing memory 
allocation work for the userspace.

thus it need to call drm_gem_object_init() function, which really the 
shmem do the backing memory

allocation.


The code path 1 and the code path 2 do not need the kernel space 
allocate the backing memory.

Because they are going to share the buffer already allocated by others.

thus, code path 2 and code path 3 should call drm_gem_private_object_init(),

*not* the drm_gem_object_init() function.


When import buffer from the a specific KMS driver,

then etnaviv_gem_prime_import_sg_table() will be called.


I guess you means that drm_gem_private_object_init() (not the 
drm_gem_object_init() function)here ?


> A better cleanup would be to make
> use of the size parameter and move this object init call into
> etnaviv_gem_new_impl.

If I following you guidance, how do I differentiate the cases

when to call drm_gem_private_object_init() not drm_gem_object_init() ?

and when call drm_gem_object_init() not drm_gem_private_object_init()?


I don't think you are right here.

> Regards,
> Lucas
>
> > Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/etnaviv/etnaviv_gem.c | 7 +++----
> >   1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > index b5f73502e3dd..be2f459c66b5 100644
> > --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> > @@ -542,7 +542,7 @@ static const struct drm_gem_object_funcs etnaviv_gem_object_funcs = {
> >   	.vm_ops = &vm_ops,
> >   };
> >   
> > -static int etnaviv_gem_new_impl(struct drm_device *dev, u32 size, u32 flags,
> > +static int etnaviv_gem_new_impl(struct drm_device *dev, u32 flags,
> >   	const struct etnaviv_gem_ops *ops, struct drm_gem_object **obj)
> >   {
> >   	struct etnaviv_gem_object *etnaviv_obj;
> > @@ -591,8 +591,7 @@ int etnaviv_gem_new_handle(struct drm_device *dev, struct drm_file *file,
> >   
> >   	size = PAGE_ALIGN(size);
> >   
> > -	ret = etnaviv_gem_new_impl(dev, size, flags,
> > -				   &etnaviv_gem_shmem_ops, &obj);
> > +	ret = etnaviv_gem_new_impl(dev, flags, &etnaviv_gem_shmem_ops, &obj);
> >   	if (ret)
> >   		goto fail;
> >   
> > @@ -627,7 +626,7 @@ int etnaviv_gem_new_private(struct drm_device *dev, size_t size, u32 flags,
> >   	struct drm_gem_object *obj;
> >   	int ret;
> >   
> > -	ret = etnaviv_gem_new_impl(dev, size, flags, ops, &obj);
> > +	ret = etnaviv_gem_new_impl(dev, flags, ops, &obj);
> >   	if (ret)
> >   		return ret;
> >