Hi Marek,
On Monday 14 December 2015 10:20:22 Marek Szyprowski wrote:
> On 2015-12-13 20:57, Laurent Pinchart wrote:
> > On Wednesday 09 December 2015 14:58:19 Marek Szyprowski wrote:
> >> Add a helper function for device drivers to set DMA's max_seg_size.
> >> Setting it to largest possible value lets DMA-mapping API always create
> >> contiguous mappings in DMA address space. This is essential for all
> >> devices, which use dma-contig videobuf2 memory allocator and shared
> >> buffers.
> >>
> >> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> >> ---
> >>
> >> drivers/media/v4l2-core/videobuf2-dma-contig.c | 15 +++++++++++++++
> >> include/media/videobuf2-dma-contig.h | 1 +
> >> 2 files changed, 16 insertions(+)
> >>
> >> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> >> b/drivers/media/v4l2-core/videobuf2-dma-contig.c index c331272..628518d
> >> 100644
> >> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> >> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> >> @@ -742,6 +742,21 @@ void vb2_dma_contig_cleanup_ctx(void *alloc_ctx)
> >>
> >> }
> >> EXPORT_SYMBOL_GPL(vb2_dma_contig_cleanup_ctx);
> >>
> >> +int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int
> >> size)
> >> +{
> >> + if (!dev->dma_parms) {
> >
> > When can this function be called with dev->dma_parms not NULL ?
>
> When one loads a module with multimedia driver (which calls this
> function), then unloads and loads it again. It is rather safe to have this
> check.
Don't you have a much bigger problem in that case ? When you unload the module
the device will be unbound from the driver, causing the memory allocated by
devm_kzalloc to be freed. dev->dma_parms will then point to freed memory,
which will get reused by all subsequent calls to dma_get_max_seg_size(),
dma_get_max_seg_size() & co (including the ones in this function).
> >> + dev->dma_parms = devm_kzalloc(dev, sizeof(dev->dma_parms),
> >> + GFP_KERNEL);
> >> + if (!dev->dma_parms)
> >> + return -ENOMEM;
> >> + }
> >> + if (dma_get_max_seg_size(dev) < size)
> >> + return dma_set_max_seg_size(dev, size);
> >> +
> >> + return 0;
> >> +}
> >> +EXPORT_SYMBOL_GPL(vb2_dma_contig_set_max_seg_size);
> >> +
> >> MODULE_DESCRIPTION("DMA-contig memory handling routines for
> >> videobuf2");
> >> MODULE_AUTHOR("Pawel Osciak <pawel@xxxxxxxxxx>");
> >> MODULE_LICENSE("GPL");
> >> diff --git a/include/media/videobuf2-dma-contig.h
> >> b/include/media/videobuf2-dma-contig.h index c33dfa6..0e6ba64 100644
> >> --- a/include/media/videobuf2-dma-contig.h
> >> +++ b/include/media/videobuf2-dma-contig.h
> >> @@ -26,6 +26,7 @@ vb2_dma_contig_plane_dma_addr(struct vb2_buffer *vb,
> >> unsigned int plane_no)
> >> void *vb2_dma_contig_init_ctx(struct device *dev);
> >> void vb2_dma_contig_cleanup_ctx(void *alloc_ctx);
> >> +int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int
> >> size);
> >> extern const struct vb2_mem_ops vb2_dma_contig_memops;
--
Regards,
Laurent Pinchart
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