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

[Christian König <christian.koenig@xxxxxxx>]

Am 20.11.23 um 16:18 schrieb Thomas Zimmermann:
> Hi
>
> Am 20.11.23 um 16:06 schrieb Felix Kuehling:
> > On 2023-11-20 6:54, Thomas Zimmermann wrote:
> > > 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?
> >
> > I'm not trying to hook into these functions, I'm just trying to call 
> > them. I'm not bringing back the .prime_handle_to_fd and 
> > .prime_fd_to_handle hooks in struct drm_driver. I need a clean way to 
> > export and import DMAbuffers from a kernel mode context. I had 
> > incorrect or semi-correct ways of doing that by calling some 
> > driver-internal functions, but then my DMABufs aren't correctly 
> > linked with GEM handles in DRM and move notifiers in amdgpu aren't 
> > working correctly.
>
> I understand that. But why don't you use drm_driver.gem_prime_import 
> and drm_gem_object_funcs.export to add the amdkfd-specific code? These 
> callbacks are being invoked from within drm_gem_prime_fd_to_handle() and
> drm_gem_prime_handle_to_fd() as part of the importing and exporting 
> logic. With the intention of doing driver-specific things. Hence you 
> should not have to re-export the internal drm_gem_prime_*_to_*() helpers.
>
> My question is if the existing hooks are not suitable for your needs. 
> If so, how could we improve them?

No no. You don't seem to understand the use case :) Felix doesn't try to 
implement any driver-specific things.

What Felix tries to do is to export a DMA-buf handle from kernel space.

Regards,
Christian.

> Best regards
> Thomas
>
>
> > Regards,
> >    Felix
> >
> >
> > > 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);