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

在 2018年05月11日 05:01, Doug Anderson 写道:
> Hi,
>
> On Wed, May 9, 2018 at 3:11 AM, William Wu <william.wu@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@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.
Ah, sorry, I'm careless.
>
>
>> - 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@chromium.org>
Thank you very much for your review. I will submit V5 patches to fix the
order of memory free in dwc2_hcd_remove(), and also add Review-by.
>
>
>


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