| Message ID | 20240622065743.385831-1-fusibrandon13@gmail.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2,v4l-utils] common: Use posix_memalign for allocating userptr buffers | expand |
Hi Brandon, On Sat, Jun 22, 2024 at 07:57:43AM +0100, 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. > > 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..4104b53 100644 > --- a/utils/common/v4l-helpers.h > +++ b/utils/common/v4l-helpers.h > @@ -1656,15 +1656,16 @@ static inline int v4l_queue_alloc_bufs(struct v4l_fd *f, > struct v4l_queue *q, unsigned from) > { > unsigned b, p; > + void *m; > + int ret; > > if (q->memory != V4L2_MEMORY_USERPTR) > 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)); Please continue declaring m and ret here. They're not used outside the loop (and should not be). > - > - if (m == NULL) > - return errno; > + ret = posix_memalign(&m, getpagesize(), v4l_queue_g_length(q, p)); Over 80 characters per line for no apparent reason. > + 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..4104b53 100644 --- a/utils/common/v4l-helpers.h +++ b/utils/common/v4l-helpers.h @@ -1656,15 +1656,16 @@ static inline int v4l_queue_alloc_bufs(struct v4l_fd *f, struct v4l_queue *q, unsigned from) { unsigned b, p; + void *m; + int ret; if (q->memory != V4L2_MEMORY_USERPTR) 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; + 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(-)