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

[wlf]

Dear Doug,

å 2018å05æ11æ 05:01, Doug Anderson åé:
> Hi,
>
> On Wed, May 9, 2018 at 3:11 AM, William Wu <william.wu@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> > ---
> > 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@xxxxxxxxxxxx>
Thank you very much for your review. I will submit V5 patches to fix the 
order of memory free in dwc2_hcd_remove()ï and also add Review-by.
>