| Message ID | 20240625112425.37172-1-fusibrandon13@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v3,v4l-utils] common: Use posix_memalign for allocating userptr buffers | expand |
Hi Brandon, On 25/06/2024 13:24, Brandon Cheo Fusi wrote: > When dealing with a userptr pointing to a buffer in userspace, > videobuf2 swaps the corresponding physical pages with other pages > so we have a contiguous area of memory for DMA. This only works if > the userptr is page aligned. > > The current way of allocating user buffers using malloc only > guarantees alignment up to `alignof(max_align_t)`, which is usually > 16. So replace malloc with posix_memalign to ensure the returned > pointer is on a page boundary. With which driver is this tested? USERPTR is really supposed to work with malloc()ed memory. There have been drivers in the past that used contiguous DMA but still allowed USERPTR, but that was a hack and these days you would use DMABUF. Regards, Hans > > Signed-off-by: Brandon Cheo Fusi <fusibrandon13@gmail.com> > --- > utils/common/v4l-helpers.h | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/utils/common/v4l-helpers.h b/utils/common/v4l-helpers.h > index cf0e92d..aa9ee26 100644 > --- a/utils/common/v4l-helpers.h > +++ b/utils/common/v4l-helpers.h > @@ -1661,10 +1661,11 @@ static inline int v4l_queue_alloc_bufs(struct v4l_fd *f, > return 0; > for (b = from; b < v4l_queue_g_buffers(q); b++) { > for (p = 0; p < v4l_queue_g_num_planes(q); p++) { > - void *m = malloc(v4l_queue_g_length(q, p)); > - > - if (m == NULL) > - return errno; > + void *m; > + int ret = posix_memalign(&m, getpagesize(), > + v4l_queue_g_length(q, p)); > + if (ret) > + return ret; > v4l_queue_s_userptr(q, b, p, m); > } > }
diff --git a/utils/common/v4l-helpers.h b/utils/common/v4l-helpers.h index cf0e92d..aa9ee26 100644 --- a/utils/common/v4l-helpers.h +++ b/utils/common/v4l-helpers.h @@ -1661,10 +1661,11 @@ static inline int v4l_queue_alloc_bufs(struct v4l_fd *f, return 0; for (b = from; b < v4l_queue_g_buffers(q); b++) { for (p = 0; p < v4l_queue_g_num_planes(q); p++) { - void *m = malloc(v4l_queue_g_length(q, p)); - - if (m == NULL) - return errno; + void *m; + int ret = posix_memalign(&m, getpagesize(), + v4l_queue_g_length(q, p)); + if (ret) + return ret; v4l_queue_s_userptr(q, b, p, m); } }
When dealing with a userptr pointing to a buffer in userspace, videobuf2 swaps the corresponding physical pages with other pages so we have a contiguous area of memory for DMA. This only works if the userptr is page aligned. The current way of allocating user buffers using malloc only guarantees alignment up to `alignof(max_align_t)`, which is usually 16. So replace malloc with posix_memalign to ensure the returned pointer is on a page boundary. Signed-off-by: Brandon Cheo Fusi <fusibrandon13@gmail.com> --- utils/common/v4l-helpers.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)