Re: [PATCH 1/3] Revert "drm/prime: Unexport helpers for fd/handle conversion"

[Christian König <christian.koenig@xxxxxxx>]

Am 20.11.23 um 12:54 schrieb Thomas Zimmermann:
> Hi
>
> Am 17.11.23 um 22:44 schrieb Felix Kuehling:
> > This reverts commit 71a7974ac7019afeec105a54447ae1dc7216cbb3.
> >
> > These helper functions are needed for KFD to export and import DMABufs
> > the right way without duplicating the tracking of DMABufs associated 
> > with
> > GEM objects while ensuring that move notifier callbacks are working as
> > intended.
>
> I'm unhappy to see these functions making a comeback. They are the 
> boiler-plate logic that all drivers should use. Historically, drivers 
> did a lot one things in their GEM code that was only semi-correct. 
> Unifying most of that made the memory management more readable. Not 
> giving back drivers to option of tinkering with this might be 
> preferable. The rsp hooks in struct drm_driver, prime_fd_to_handle and 
> prime_handle_to_fd, are only there for vmwgfx.
>
> If you want to hook into prime import and export, there are 
> drm_driver.gem_prime_import and drm_gem_object_funcs.export. Isn't it 
> possible to move the additional code behind these pointers?

No, the problem here is that the KFD code wants to create DMA-buf 
exports for GEM buffers but from a different file descriptor than the 
DRM render or primary node.

Essentially the KFD node is a separate file descriptor AMD GPUs came up 
with for supporting compute.

Regards,
Christian.

> Best regards
> Thomas
>
> > CC: Christian König <christian.koenig@xxxxxxx>
> > CC: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > Signed-off-by: Felix Kuehling <Felix.Kuehling@xxxxxxx>
> > ---
> >   drivers/gpu/drm/drm_prime.c | 33 ++++++++++++++++++---------------
> >   include/drm/drm_prime.h     |  7 +++++++
> >   2 files changed, 25 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> > index 63b709a67471..834a5e28abbe 100644
> > --- a/drivers/gpu/drm/drm_prime.c
> > +++ b/drivers/gpu/drm/drm_prime.c
> > @@ -278,7 +278,7 @@ void drm_gem_dmabuf_release(struct dma_buf *dma_buf)
> >   }
> >   EXPORT_SYMBOL(drm_gem_dmabuf_release);
> >   -/*
> > +/**
> >    * drm_gem_prime_fd_to_handle - PRIME import function for GEM drivers
> >    * @dev: drm_device to import into
> >    * @file_priv: drm file-private structure
> > @@ -292,9 +292,9 @@ EXPORT_SYMBOL(drm_gem_dmabuf_release);
> >    *
> >    * Returns 0 on success or a negative error code on failure.
> >    */
> > -static int drm_gem_prime_fd_to_handle(struct drm_device *dev,
> > -                      struct drm_file *file_priv, int prime_fd,
> > -                      uint32_t *handle)
> > +int drm_gem_prime_fd_to_handle(struct drm_device *dev,
> > +                   struct drm_file *file_priv, int prime_fd,
> > +                   uint32_t *handle)
> >   {
> >       struct dma_buf *dma_buf;
> >       struct drm_gem_object *obj;
> > @@ -360,6 +360,7 @@ static int drm_gem_prime_fd_to_handle(struct 
> > drm_device *dev,
> >       dma_buf_put(dma_buf);
> >       return ret;
> >   }
> > +EXPORT_SYMBOL(drm_gem_prime_fd_to_handle);
> >     int drm_prime_fd_to_handle_ioctl(struct drm_device *dev, void *data,
> >                    struct drm_file *file_priv)
> > @@ -408,7 +409,7 @@ static struct dma_buf 
> > *export_and_register_object(struct drm_device *dev,
> >       return dmabuf;
> >   }
> >   -/*
> > +/**
> >    * drm_gem_prime_handle_to_fd - PRIME export function for GEM drivers
> >    * @dev: dev to export the buffer from
> >    * @file_priv: drm file-private structure
> > @@ -421,10 +422,10 @@ static struct dma_buf 
> > *export_and_register_object(struct drm_device *dev,
> >    * The actual exporting from GEM object to a dma-buf is done 
> > through the
> >    * &drm_gem_object_funcs.export callback.
> >    */
> > -static int drm_gem_prime_handle_to_fd(struct drm_device *dev,
> > -                      struct drm_file *file_priv, uint32_t handle,
> > -                      uint32_t flags,
> > -                      int *prime_fd)
> > +int drm_gem_prime_handle_to_fd(struct drm_device *dev,
> > +                   struct drm_file *file_priv, uint32_t handle,
> > +                   uint32_t flags,
> > +                   int *prime_fd)
> >   {
> >       struct drm_gem_object *obj;
> >       int ret = 0;
> > @@ -506,6 +507,7 @@ static int drm_gem_prime_handle_to_fd(struct 
> > drm_device *dev,
> >         return ret;
> >   }
> > +EXPORT_SYMBOL(drm_gem_prime_handle_to_fd);
> >     int drm_prime_handle_to_fd_ioctl(struct drm_device *dev, void *data,
> >                    struct drm_file *file_priv)
> > @@ -864,9 +866,9 @@ EXPORT_SYMBOL(drm_prime_get_contiguous_size);
> >    * @obj: GEM object to export
> >    * @flags: flags like DRM_CLOEXEC and DRM_RDWR
> >    *
> > - * This is the implementation of the &drm_gem_object_funcs.export 
> > functions
> > - * for GEM drivers using the PRIME helpers. It is used as the 
> > default for
> > - * drivers that do not set their own.
> > + * This is the implementation of the &drm_gem_object_funcs.export 
> > functions for GEM drivers
> > + * using the PRIME helpers. It is used as the default in
> > + * drm_gem_prime_handle_to_fd().
> >    */
> >   struct dma_buf *drm_gem_prime_export(struct drm_gem_object *obj,
> >                        int flags)
> > @@ -962,9 +964,10 @@ EXPORT_SYMBOL(drm_gem_prime_import_dev);
> >    * @dev: drm_device to import into
> >    * @dma_buf: dma-buf object to import
> >    *
> > - * This is the implementation of the gem_prime_import functions for GEM
> > - * drivers using the PRIME helpers. It is the default for drivers 
> > that do
> > - * not set their own &drm_driver.gem_prime_import.
> > + * This is the implementation of the gem_prime_import functions for 
> > GEM drivers
> > + * using the PRIME helpers. Drivers can use this as their
> > + * &drm_driver.gem_prime_import implementation. It is used as the 
> > default
> > + * implementation in drm_gem_prime_fd_to_handle().
> >    *
> >    * Drivers must arrange to call drm_prime_gem_destroy() from their
> >    * &drm_gem_object_funcs.free hook when using this function.
> > diff --git a/include/drm/drm_prime.h b/include/drm/drm_prime.h
> > index a7abf9f3e697..2a1d01e5b56b 100644
> > --- a/include/drm/drm_prime.h
> > +++ b/include/drm/drm_prime.h
> > @@ -60,12 +60,19 @@ enum dma_data_direction;
> >     struct drm_device;
> >   struct drm_gem_object;
> > +struct drm_file;
> >     /* core prime functions */
> >   struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
> >                         struct dma_buf_export_info *exp_info);
> >   void drm_gem_dmabuf_release(struct dma_buf *dma_buf);
> >   +int drm_gem_prime_fd_to_handle(struct drm_device *dev,
> > +                   struct drm_file *file_priv, int prime_fd, 
> > uint32_t *handle);
> > +int drm_gem_prime_handle_to_fd(struct drm_device *dev,
> > +                   struct drm_file *file_priv, uint32_t handle, 
> > uint32_t flags,
> > +                   int *prime_fd);
> > +
> >   /* helper functions for exporting */
> >   int drm_gem_map_attach(struct dma_buf *dma_buf,
> >                  struct dma_buf_attachment *attach);