Am 08.10.20 um 16:14 schrieb Daniel Vetter:
On Thu, Oct 08, 2020 at 04:09:14PM +0200, Daniel Vetter wrote:
On Thu, Oct 08, 2020 at 01:23:40PM +0200, Christian König wrote:
We have reoccurring requests on this so better document that
this approach doesn't work and dma_buf_mmap() needs to be used instead.
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/gpu/drm/drm_prime.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 4910c446db83..16fa2bfc271e 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -956,7 +956,7 @@ EXPORT_SYMBOL(drm_gem_prime_import);
/**
* drm_prime_sg_to_page_addr_arrays - convert an sg table into a page array
* @sgt: scatter-gather table to convert
- * @pages: optional array of page pointers to store the page array in
+ * @pages: deprecated array of page pointers to store the page array in
* @addrs: optional array to store the dma bus address of each page
* @max_entries: size of both the passed-in arrays
*
@@ -965,6 +965,11 @@ EXPORT_SYMBOL(drm_gem_prime_import);
*
* Drivers can use this in their &drm_driver.gem_prime_import_sg_table
* implementation.
+ *
+ * Specifying the pages array is deprecated and strongly discouraged for new
+ * drivers. The pages array is only useful for page faults and those can
+ * corrupt fields in the struct page if they are not handled by the exporting
+ * driver.
*/
I'd make this a _lot_ stronger: Aside from amdgpu and radeon all drivers
using this only need it for the pages array. Imo just open-code the sg
table walking loop in amdgpu/radeon (it's really not much code), and then
drop the dma_addr_t parameter from this function here (it's set to NULL by
everyone else).
And then deprecate this entire function here with a big warning that a)
dma_buf_map_attachment is allowed to leave the struct page pointers NULL
and b) this breaks mmap, users must call dma_buf_mmap instead.
Also maybe make it an uppercase DEPRECATED or something like that :-)
OK I just realized I missed nouveau. That would be 3 places where we need
to stuff the dma_addr_t list into something ttm can take. Still feels
better than this half-deprecated function kludge ...
Mhm, I don't see a reason why nouveau would need the struct page either.
How about we split that up into two function?
One for converting the sg_table into a linear dma_addr array.
And one for converting the sg_table into a linear struct page array with
a __deprecated attribute on it?
Christian.
-Daniel
-Daniel
int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
dma_addr_t *addrs, int max_entries)
--
2.17.1
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
