linux-kernel - Re: [PATCH 2/2] usb: dwc2: fix isoc split in transfer with no data

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Date:   Tue, 24 Apr 2018 11:27:04 +0300
From:   Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:     William Wu <william.wu@...k-chips.com>, hminas@...opsys.com,
        felipe.balbi@...ux.intel.com, gregkh@...uxfoundation.org
Cc:     heiko@...ech.de, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        frank.wang@...k-chips.com, huangtao@...k-chips.com,
        dianders@...gle.com, daniel.meng@...k-chips.com,
        John.Youn@...opsys.com, wzz@...k-chips.com, zsq@...k-chips.com,
        Allen.Hsu@...ntatw.com, StanTsui@...EN.com
Subject: Re: [PATCH 2/2] usb: dwc2: fix isoc split in transfer with no data

Hello!

On 4/24/2018 5:43 AM, William Wu wrote:

> If isoc split in transfer with no data (the length of DATA0
> packet is 0), we can't simply return immediately. Because the
> DATA0 can be the first transaction or the second transaction for
> the isoc split in transaction. If the DATA0 packet with on data
                                                           ^^ no?

> is in the first transaction, we can return immediately. But if
> the the DATA0 packet with on data is in the second transaction

   One "the" too many. And that "on data" again... :-)

> of isoc split in transaction sequence, we need to increase the
> qtd->isoc_frame_index and giveback urb to device driver if needed,
> otherwise, the MDATA packet will be lost.
> 
> A typical test case is that 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.
> 
> In the case, the isoc split in transaction sequence like this:
> 
> - SSPLIT IN transaction
> - CSPLIT IN transaction
>    - MDATA packet (176 bytes)
> - CSPLIT IN transaction
>    - DATA0 packet (0 byte)
> 
> This patch use both the length of DATA0 and qtd->isoc_split_offset
> to check if the DATA0 is in the second transaction.
> 
> Signed-off-by: William Wu <william.wu@...k-chips.com>
[...]

MBR, Sergei