Re: [PATCH 2/6] drm/ttm: Store the bo_kmap_type in struct iosys_map

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 14.06.24 um 16:31 schrieb Christian König:
> Am 14.06.24 um 15:21 schrieb Thomas Zimmermann:
> > For each instances of struct iosys_map set up by ttm_bo_vmap(), store
> > the type of allocation in the instance. Use this information to unmap
> > the memory in ttm_bo_vunmap(). This change simplifies the unmap code
> > and puts the complicated logic entirely into the map code.
>
> I'm not sure that's a good idea.
>
> The mapping information should already be available in the resource 
> and storing it in the iosys_map structures duplicates that information.
>
> So we might run into the issue that the resource has changed and so we 
> need a different approach now, but the iosys_map will say that we 
> should unmap things for example.

Patches 1 and 2 are only here to make patch 4 (add the kmap special 
case) work. How can I distinguish between vmap'ed and kmap'ed memory? 
It's not clear to me, whether there is a benefit from patch 4. The xe 
driver makes it sound like that, but the rest of the kernel appears to 
disagree.

Best regards
Thomas

> Regards,
> Christian.
>
> > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > ---
> >   drivers/gpu/drm/ttm/ttm_bo_util.c | 46 +++++++++++++++++++++----------
> >   1 file changed, 31 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c 
> > b/drivers/gpu/drm/ttm/ttm_bo_util.c
> > index 0b3f4267130c4..a9df0deff2deb 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> > @@ -36,6 +36,7 @@
> >   #include <drm/ttm/ttm_tt.h>
> >     #include <drm/drm_cache.h>
> > +#include <drm/drm_device.h>
> >     struct ttm_transfer_obj {
> >       struct ttm_buffer_object base;
> > @@ -479,24 +480,29 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, 
> > struct iosys_map *map)
> >         if (mem->bus.is_iomem) {
> >           void __iomem *vaddr_iomem;
> > +        u16 alloc_flags;
> >   -        if (mem->bus.addr)
> > +        if (mem->bus.addr) {
> >               vaddr_iomem = (void __iomem *)mem->bus.addr;
> > -        else if (mem->bus.caching == ttm_write_combined)
> > -            vaddr_iomem = ioremap_wc(mem->bus.offset,
> > -                         bo->base.size);
> > +            alloc_flags = ttm_bo_map_premapped;
> > +        } else if (mem->bus.caching == ttm_write_combined) {
> > +            vaddr_iomem = ioremap_wc(mem->bus.offset, bo->base.size);
> > +            alloc_flags = ttm_bo_map_iomap;
> >   #ifdef CONFIG_X86
> > -        else if (mem->bus.caching == ttm_cached)
> > -            vaddr_iomem = ioremap_cache(mem->bus.offset,
> > -                          bo->base.size);
> > +        } else if (mem->bus.caching == ttm_cached) {
> > +            vaddr_iomem = ioremap_cache(mem->bus.offset, 
> > bo->base.size);
> > +            alloc_flags = ttm_bo_map_iomap;
> >   #endif
> > -        else
> > +        } else {
> >               vaddr_iomem = ioremap(mem->bus.offset, bo->base.size);
> > +            alloc_flags = ttm_bo_map_iomap;
> > +        }
> >             if (!vaddr_iomem)
> >               return -ENOMEM;
> >             iosys_map_set_vaddr_iomem(map, vaddr_iomem);
> > +        map->alloc_flags = alloc_flags;
> >         } else {
> >           struct ttm_operation_ctx ctx = {
> > @@ -506,6 +512,7 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, 
> > struct iosys_map *map)
> >           struct ttm_tt *ttm = bo->ttm;
> >           pgprot_t prot;
> >           void *vaddr;
> > +        u16 alloc_flags;
> >             ret = ttm_tt_populate(bo->bdev, ttm, &ctx);
> >           if (ret)
> > @@ -519,8 +526,10 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, 
> > struct iosys_map *map)
> >           vaddr = vmap(ttm->pages, ttm->num_pages, 0, prot);
> >           if (!vaddr)
> >               return -ENOMEM;
> > +        alloc_flags = ttm_bo_map_vmap;
> >             iosys_map_set_vaddr(map, vaddr);
> > +        map->alloc_flags = alloc_flags;
> >       }
> >         return 0;
> > @@ -537,20 +546,27 @@ EXPORT_SYMBOL(ttm_bo_vmap);
> >    */
> >   void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct iosys_map 
> > *map)
> >   {
> > -    struct ttm_resource *mem = bo->resource;
> > -
> >       dma_resv_assert_held(bo->base.resv);
> >         if (iosys_map_is_null(map))
> >           return;
> >   -    if (!map->is_iomem)
> > -        vunmap(map->vaddr);
> > -    else if (!mem->bus.addr)
> > +    switch (map->alloc_flags) {
> > +    case ttm_bo_map_iomap:
> >           iounmap(map->vaddr_iomem);
> > -    iosys_map_clear(map);
> > -
> > +        break;
> > +    case ttm_bo_map_vmap:
> > +        vunmap(map->vaddr);
> > +        break;
> > +    case ttm_bo_map_premapped:
> > +        break;
> > +    default:
> > +        drm_err(bo->base.dev, "Unsupported alloc_flags 0x%x\n", 
> > map->alloc_flags);
> > +        return;
> > +    }
> >       ttm_mem_io_free(bo->bdev, bo->resource);
> > +
> > +    iosys_map_clear(map);
> >   }
> >   EXPORT_SYMBOL(ttm_bo_vunmap);

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)