[PATCH v2 1/2] drm/shmem: add support for per object caching attributes
Daniel Vetter
daniel at ffwll.ch
Wed Dec 11 12:36:35 UTC 2019
On Wed, Dec 11, 2019 at 11:07:25AM +0100, Thomas Zimmermann wrote:
>
>
> Am 11.12.19 um 10:58 schrieb Thomas Zimmermann:
> > Hi Gerd
> >
> > Am 11.12.19 um 09:18 schrieb Gerd Hoffmann:
> >> Add caching field to drm_gem_shmem_object to specify the cachine
> >> attributes for mappings. Add helper function to tweak pgprot
> >> accordingly. Switch vmap and mmap functions to the new helper.
> >>
> >> Set caching to write-combine when creating the object so behavior
> >> doesn't change by default. Drivers can override that later if
> >> needed.
> >>
> >> Signed-off-by: Gerd Hoffmann <kraxel at redhat.com>
> >
> > If you want to merge this patch, you have my
> >
> > Reviewed-by: Thomas Zimmermann <tzimmermann at suse.de>
> >
> > Please see my comment below.
> >
> >> ---
> >> include/drm/drm_gem_shmem_helper.h | 12 ++++++++++++
> >> drivers/gpu/drm/drm_gem_shmem_helper.c | 24 +++++++++++++++++++++---
> >> 2 files changed, 33 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> >> index 6748379a0b44..9d6e02c6205f 100644
> >> --- a/include/drm/drm_gem_shmem_helper.h
> >> +++ b/include/drm/drm_gem_shmem_helper.h
> >> @@ -17,6 +17,11 @@ struct drm_mode_create_dumb;
> >> struct drm_printer;
> >> struct sg_table;
> >>
> >> +enum drm_gem_shmem_caching {
> >> + DRM_GEM_SHMEM_CACHED = 1,
> >> + DRM_GEM_SHMEM_WC,
> >> +};
> >> +
> >> /**
> >> * struct drm_gem_shmem_object - GEM object backed by shmem
> >> */
> >> @@ -83,6 +88,11 @@ struct drm_gem_shmem_object {
> >> * The address are un-mapped when the count reaches zero.
> >> */
> >> unsigned int vmap_use_count;
> >> +
> >> + /**
> >> + * @caching: caching attributes for mappings.
> >> + */
> >> + enum drm_gem_shmem_caching caching;
> >> };
> >>
> >> #define to_drm_gem_shmem_obj(obj) \
> >> @@ -130,6 +140,8 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
> >>
> >> struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_object *obj);
> >>
> >> +pgprot_t drm_gem_shmem_caching(struct drm_gem_shmem_object *shmem, pgprot_t prot);
> >> +
> >> /**
> >> * DRM_GEM_SHMEM_DRIVER_OPS - Default shmem GEM operations
> >> *
> >> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> >> index a421a2eed48a..5bb94e130a50 100644
> >> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> >> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> >> @@ -76,6 +76,7 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t
> >> mutex_init(&shmem->pages_lock);
> >> mutex_init(&shmem->vmap_lock);
> >> INIT_LIST_HEAD(&shmem->madv_list);
> >> + shmem->caching = DRM_GEM_SHMEM_WC;
> >>
> >> /*
> >> * Our buffers are kept pinned, so allocating them
> >> @@ -256,9 +257,11 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
> >>
> >> if (obj->import_attach)
> >> shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
> >> - else
> >> + else {
> >> + pgprot_t prot = drm_gem_shmem_caching(shmem, PAGE_KERNEL);
> >> shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
> >> - VM_MAP, pgprot_writecombine(PAGE_KERNEL));
> >> + VM_MAP, prot);
> >> + }
> >>
> >> if (!shmem->vaddr) {
> >> DRM_DEBUG_KMS("Failed to vmap pages\n");
> >> @@ -540,7 +543,8 @@ int drm_gem_shmem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> >> }
> >>
> >> vma->vm_flags |= VM_MIXEDMAP | VM_DONTEXPAND;
> >> - vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
> >> + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
> >> + vma->vm_page_prot = drm_gem_shmem_caching(shmem, vma->vm_page_prot);
> >> vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
> >> vma->vm_ops = &drm_gem_shmem_vm_ops;
> >>
> >> @@ -683,3 +687,17 @@ drm_gem_shmem_prime_import_sg_table(struct drm_device *dev,
> >> return ERR_PTR(ret);
> >> }
> >> EXPORT_SYMBOL_GPL(drm_gem_shmem_prime_import_sg_table);
> >> +
> >> +pgprot_t drm_gem_shmem_caching(struct drm_gem_shmem_object *shmem, pgprot_t prot)
> >> +{
> >> + switch (shmem->caching) {
> >> + case DRM_GEM_SHMEM_CACHED:
> >> + return prot;
> >> + case DRM_GEM_SHMEM_WC:
> >> + return pgprot_writecombine(prot);
> >> + default:
> >> + WARN_ON_ONCE(1);
> >> + return prot;
> >> + }
> >> +}
> >> +EXPORT_SYMBOL_GPL(drm_gem_shmem_caching);
> >
> > Two reason why I'd reconsider this design.
> >
> > I don't like switch statements new the bottom of the call graph. The
> > code ends up with default warnings, such as this one.
> >
> > Udl has different caching flags for imported and 'native' buffers. This
> > would require a new constant and additional code here.
> >
> > What do you think about turning this function into a callback in struct
> > shmem_funcs? The default implementation would be for WC, virtio would
> > use CACHED. The individual implementations could still be located in the
> > shmem code. Udl would later provide its own code.
>
> On a second thought, all this might be over-engineered and v1 of the
> patchset was the correct approach. You can add my
The udl use-case should be covered already, simply set the flag correctly
at create/import time? It's per-object ...
btw on why udl does this: Imported bo are usually rendered by real hw, and
reading it uncached/wc is the more defensive setting. It would be kinda
nice if dma-buf would expose this, but I fear dma-api maintainers would
murder us if we even just propose that ... so it's a mess right now.
btw the issue extends to dma access by devices too, e.g. both i915 and
amdgpu can select the coherency mode at runtime (using e.g. the pcie
no-snoop transaction mode), and we have similar uncoordinated hacks in
there too, like in udl.
-Daniel
>
> Acked-by: Thomas Zimmermann <tzimmermann at suse.de>
>
> if you prefer to merge v1.
>
> >
> > Best regards
> > Thomas
> >
> >>
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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