[PATCH v4 1/2] usb: dwc2: alloc dma aligned buffer for isoc split in

Doug Anderson dianders at google.com
Thu May 10 14:01:59 PDT 2018


On Wed, May 9, 2018 at 3:11 AM, William Wu <william.wu at rock-chips.com> wrote:
> The commit 3bc04e28a030 ("usb: dwc2: host: Get aligned DMA in
> a more supported way") rips out a lot of code to simply the
> allocation of aligned DMA. However, it also introduces a new
> issue when use isoc split in transfer.
> In my test case, I connect the dwc2 controller with an usb hs
> Hub (GL852G-12), and plug an usb fs audio device (Plantronics
> headset) into the downstream port of Hub. Then use the usb mic
> to record, we can find noise when playback.
> It's because that the usb Hub uses an MDATA for the first
> transaction and a DATA0 for the second transaction for the isoc
> split in transaction. An typical isoc split in transaction sequence
> like this:
> - SSPLIT IN transaction
> - CSPLIT IN transaction
>   - MDATA packet
> - CSPLIT IN transaction
>   - DATA0 packet
> The DMA address of MDATA (urb->dma) is always DWORD-aligned, but
> the DMA address of DATA0 (urb->dma + qtd->isoc_split_offset) may
> not be DWORD-aligned, it depends on the qtd->isoc_split_offset (the
> length of MDATA). In my test case, the length of MDATA is usually
> unaligned, this cause DATA0 packet transmission error.
> This patch use kmem_cache to allocate aligned DMA buf for isoc
> split in transaction. Note that according to usb 2.0 spec, the
> maximum data payload size is 1023 bytes for each fs isoc ep,
> and the maximum allowable interrupt data payload size is 64 bytes
> or less for fs interrupt ep. So we set the size of object to be
> 1024 bytes in the kmem cache.
> Signed-off-by: William Wu <william.wu at rock-chips.com>
> ---
> Changes in v4:
> - get rid of "qh->dw_align_buf_size"
> - allocate unaligned_cache for Address DMA mode and Desc DMA mode
> - freeing order opposite of allocation

You only did half of this.  You changed the order under "error4" but
forgot to make dwc2_hcd_remove() match.

> - do dma_map_single() with the size of DWC2_KMEM_UNALIGNED_BUF_SIZE
> Changes in v3:
> - Modify the commit message
> - Use Kmem_cache to allocate aligned DMA buf
> - Fix coding style
> Changes in v2:
> - None
>  drivers/usb/dwc2/core.h      |  3 ++
>  drivers/usb/dwc2/hcd.c       | 87 ++++++++++++++++++++++++++++++++++++++++++--
>  drivers/usb/dwc2/hcd.h       |  8 ++++
>  drivers/usb/dwc2/hcd_intr.c  |  8 ++++
>  drivers/usb/dwc2/hcd_queue.c |  3 ++
>  5 files changed, 105 insertions(+), 4 deletions(-)

My only remaining comment is a really nitty detail.  Unless someone
else feels strongly about it, I'm not sure it's worth spinning the
patch just for that nit unless someone else has review comments.

I believe I've looked at this enough to say:

Reviewed-by: Douglas Anderson <dianders at chromium.org>

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