Re: [PATCH v5 0/3] add dma noncoherent API

[Hans de Goede <hansg@kernel.org>]

Hi all,

On 4-Jul-25 11:57, Xu Yang wrote:
> On architectures where there is no coherent caching such as ARM it's
> proved that using dma_alloc_noncontiguous API and handling manually
> the cache flushing will significantly improve performance.
> 
> Refer to:
> commit 20e1dbf2bbe2 ("media: uvcvideo: Use dma_alloc_noncontiguous API")
> commit 68d0c3311ec1 ("media: stk1160: use dma_alloc_noncontiguous API")
> 
> However, it's obvious that there is significant code duplication between
> these two commits. Besides, a potential user USB Monitor may read outdated
> data before the driver do DMA sync for CPU which will make the data
> unreliable.
> 
> To reduce code duplication and avoid USB Monitor result unreliable, this
> series will introduce DMA noncoherent API to USB core. And the USB core
> layer will manage synchronization itself.
> 
> Then the last 2 patches have used the API.
> 
> I have tested uvcvideo driver. But I haven't tested stk1160 driver as I
> don't have such boards. @Ezequiel Garcia, @Dafna Hirschfeld do you have
> time to test it? Your support on this would be greatly appreciated.

It seems that patches 1 + 2 are ready for merging now
(for patch 3 we should probably wait for testing).

I think that it would be best for both patches 1 + 2 to
be merged through the USB tree. The changed code in the UVC
driver is not touched that often so I do not expect any
conflicts.

Regards,

Hans




> Changes in v5:
>  - improve if-else logic as suggested by Andy and Alan.
>  - add Reviewed-by tag
> 
> Changes in v4:
>  - https://lore.kernel.org/all/20250703103811.4048542-1-xu.yang_2@nxp.com/
>  - improve if-else logic
>  - remove uvc_stream_to_dmadev()
> 
> Changes in v3:
>  - https://lore.kernel.org/all/20250702110222.3926355-1-xu.yang_2@nxp.com/
>  - put Return section at the end of description
>  - correct some abbreviations
>  - remove usb_dma_noncoherent_sync_for_cpu() and
>    usb_dma_noncoherent_sync_for_device()
>  - do DMA sync in usb_hcd_map_urb_for_dma() and
>    usb_hcd_unmap_urb_for_dma()
>  - call flush_kernel_vmap_range() for OUT transfers
>    and invalidate_kernel_vmap_range() for IN transfers 
> 
> Changes in v2:
>  - https://lore.kernel.org/all/20250627101939.3649295-1-xu.yang_2@nxp.com/
>  - handle it in USB core
> 
> v1:
>  - https://lore.kernel.org/linux-usb/20250614132446.251218-1-xu.yang_2@nxp.com/
> 
> Xu Yang (3):
>   usb: core: add dma-noncoherent buffer alloc and free API
>   media: uvcvideo: use usb_alloc_noncoherent/usb_free_noncoherent()
>   media: stk1160: use usb_alloc_noncoherent/usb_free_noncoherent()
> 
>  drivers/media/usb/stk1160/stk1160-v4l.c   |  4 --
>  drivers/media/usb/stk1160/stk1160-video.c | 43 ++++--------
>  drivers/media/usb/stk1160/stk1160.h       |  7 --
>  drivers/media/usb/uvc/uvc_video.c         | 61 ++++-------------
>  drivers/usb/core/hcd.c                    | 29 +++++---
>  drivers/usb/core/usb.c                    | 80 +++++++++++++++++++++++
>  include/linux/usb.h                       | 11 ++++
>  7 files changed, 137 insertions(+), 98 deletions(-)
>