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SubjectRe: [PATCH v10 06/11] drm/shmem-helper: Don't use vmap_use_count for dma-bufs
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Hi

Am 08.01.23 um 22:04 schrieb Dmitry Osipenko:
> DMA-buf core has its own refcounting of vmaps, use it instead of drm-shmem
> counting. This change prepares drm-shmem for addition of memory shrinker
> support where drm-shmem will use a single dma-buf reservation lock for
> all operations performed over dma-bufs.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>

with my comments below considered.

> ---
> drivers/gpu/drm/drm_gem_shmem_helper.c | 35 +++++++++++++++-----------
> 1 file changed, 20 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 5006f7da7f2d..1392cbd3cc02 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -301,24 +301,22 @@ static int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem,
> struct drm_gem_object *obj = &shmem->base;
> int ret = 0;
>
> - if (shmem->vmap_use_count++ > 0) {
> - iosys_map_set_vaddr(map, shmem->vaddr);
> - return 0;
> - }
> -
> if (obj->import_attach) {
> ret = dma_buf_vmap(obj->import_attach->dmabuf, map);
> if (!ret) {
> if (drm_WARN_ON(obj->dev, map->is_iomem)) {

I'm sure that I added this line at some point. But I'm now wondering why
we're testing this flag. Everything that uses the mapped buffer should
by agnostic to is_iomem. IIRC the only reason for this test is is that
we're setting shmem->vaddr to the returned map->vaddr. Now that the code
is gone, we can also remove that whole branch.

> dma_buf_vunmap(obj->import_attach->dmabuf, map);
> - ret = -EIO;
> - goto err_put_pages;
> + return -EIO;
> }
> - shmem->vaddr = map->vaddr;
> }
> } else {
> pgprot_t prot = PAGE_KERNEL;
>
> + if (shmem->vmap_use_count++ > 0) {
> + iosys_map_set_vaddr(map, shmem->vaddr);
> + return 0;
> + }
> +
> ret = drm_gem_shmem_get_pages(shmem);
> if (ret)
> goto err_zero_use;
> @@ -384,15 +382,15 @@ static void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem,
> {
> struct drm_gem_object *obj = &shmem->base;
>
> - if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
> - return;
> -
> - if (--shmem->vmap_use_count > 0)
> - return;
> -
> if (obj->import_attach) {
> dma_buf_vunmap(obj->import_attach->dmabuf, map);
> } else {
> + if (drm_WARN_ON_ONCE(obj->dev, !shmem->vmap_use_count))
> + return;
> +
> + if (--shmem->vmap_use_count > 0)
> + return;
> +
> vunmap(shmem->vaddr);
> drm_gem_shmem_put_pages(shmem);
> }
> @@ -660,7 +658,14 @@ void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
> struct drm_printer *p, unsigned int indent)
> {
> drm_printf_indent(p, indent, "pages_use_count=%u\n", shmem->pages_use_count);
> - drm_printf_indent(p, indent, "vmap_use_count=%u\n", shmem->vmap_use_count);
> +
> + if (shmem->base.import_attach)
> + drm_printf_indent(p, indent, "vmap_use_count=%u\n",
> + shmem->base.dma_buf->vmapping_counter);

This is not vmap_use_count and the best solution is to add a print_info
callback to dma_bufs. So Maybe simply ignore imported buffers here.

Best regards
Thomas

> + else
> + drm_printf_indent(p, indent, "vmap_use_count=%u\n",
> + shmem->vmap_use_count);
> +
> drm_printf_indent(p, indent, "vaddr=%p\n", shmem->vaddr);
> }
> EXPORT_SYMBOL(drm_gem_shmem_print_info);

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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