linux-kernel - Re: [PATCH v3] usb: gadget: musb: fix short isoc packets with inventra dma

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Message-ID: <20190116153322.GG18026@uda0271908>
Date:   Wed, 16 Jan 2019 09:33:22 -0600
From:   Bin Liu <b-liu@...com>
To:     Paul Elder <paul.elder@...asonboard.com>
CC:     <laurent.pinchart@...asonboard.com>,
        <kieran.bingham@...asonboard.com>, <drinkcat@...omium.org>,
        <balbi@...nel.org>, <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] usb: gadget: musb: fix short isoc packets with
 inventra dma

On Tue, Jan 15, 2019 at 07:01:45PM -0500, Paul Elder wrote:
> Handling short packets (length < max packet size) in the Inventra DMA
> engine in the MUSB driver causes the MUSB DMA controller to hang. An
> example of a problem that is caused by this problem is when streaming
> video out of a UVC gadget, only the first video frame is transferred.
> 
> For short packets (mode-0 or mode-1 DMA), MUSB_TXCSR_TXPKTRDY must be
> set manually by the driver. This was previously done in musb_g_tx
> (musb_gadget.c), but incorrectly (all csr flags were cleared, and only
> MUSB_TXCSR_MODE and MUSB_TXCSR_TXPKTRDY were set). Fixing that problem
> allows some requests to be transferred correctly, but multiple requests
> were often put together in one USB packet, and caused problems if the
> packet size was not a multiple of 4. Instead, set MUSB_TXCSR_TXPKTRDY
> in dma_controller_irq (musbhsdma.c), just like host mode transfers.
> 
> This topic was originally tackled by Nicolas Boichat [0] [1] and is
> discussed further at [2] as part of his GSoC project [3].
> 
> [0] https://groups.google.com/forum/?hl=en#!topic/beagleboard-gsoc/k8Azwfp75CU
> [1] https://gitorious.org/beagleboard-usbsniffer/beagleboard-usbsniffer-kernel/commit/b0be3b6cc195ba732189b04f1d43ec843c3e54c9?p=beagleboard-usbsniffer:beagleboard-usbsniffer-kernel.git;a=patch;h=b0be3b6cc195ba732189b04f1d43ec843c3e54c9
> [2] http://beagleboard-usbsniffer.blogspot.com/2010/07/musb-isochronous-transfers-fixed.html
> [3] http://elinux.org/BeagleBoard/GSoC/USBSniffer
> 
> Signed-off-by: Paul Elder <paul.elder@...asonboard.com>
> ---
> Changes in v3:
> 
> - remove unnecessary chunk for sending short packet
> 
> Changes in v2:
> 
> - no more flushing FIFO
> - greatly simplified short packet if guard in musb_g_tx, and removed
>   unnecessary variables
> - minor indentation and wording changes
>  drivers/usb/musb/musb_gadget.c | 13 +------------
>  drivers/usb/musb/musbhsdma.c   | 21 +++++++++++----------
>  2 files changed, 12 insertions(+), 22 deletions(-)

Applied. Thanks.

Regards,
-Bin.