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

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Message-ID: <CAD=FV=VGhnQ2NQqn+HYNadxor8a4gNwj8hmSvGXxxstKiUJmdA@mail.gmail.com>
Date:   Thu, 10 May 2018 14:01:59 -0700
From:   Doug Anderson <dianders@...gle.com>
To:     William Wu <william.wu@...k-chips.com>
Cc:     hminas@...opsys.com, felipe.balbi@...ux.intel.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Heiko Stübner <heiko@...ech.de>,
        LKML <linux-kernel@...r.kernel.org>, linux-usb@...r.kernel.org,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Frank Wang <frank.wang@...k-chips.com>,
        黄涛 <huangtao@...k-chips.com>,
        "daniel.meng" <daniel.meng@...k-chips.com>,
        John Youn <John.Youn@...opsys.com>,
        王征增 <wzz@...k-chips.com>,
        zsq@...k-chips.com,
        許嘉銘 <Allen.Hsu@...ntatw.com>,
        Stan Tsui <StanTsui@...en.com>,
        Spruce Wu (吳建勳) <Spruce.Wu@...ntatw.com>,
        Martin Tsai <Martin.Tsai@...ntatw.com>,
        Kevin Hsueh <Kevin.Shai@...ntatw.com>,
        Mon-Jer Wu (吳孟哲) 
        <Mon-Jer.Wu@...ntatw.com>,
        Claud Chang (張恭築) 
        <Claud.Chang@...ntatw.com>,
        San Lin (林建菱) <San.Lin@...ntatw.com>,
        Ren Kuo <Ren.Kuo@...ntatw.com>,
        "David H.T. Wang" <davidhtwang@...en.com>,
        Fong Lin <fonglin@...en.com>,
        Steven Cheng <stevencheng@...en.com>,
        Tom Chen <tomchen@...en.com>, Don Chang <donchang@...en.com>,
        milesschofield@...en.com
Subject: Re: [PATCH v4 1/2] usb: dwc2: alloc dma aligned buffer for isoc split in

Hi,

On Wed, May 9, 2018 at 3:11 AM, William Wu <william.wu@...k-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@...k-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@...omium.org>