[1/1] usb: gadget: musb: fix short isoc packets with inventra dma

[Bin Liu <b-liu@ti.com>]

Greg,

On Wed, Jan 30, 2019 at 09:24:04AM +0100, Greg Kroah-Hartman wrote:
> On Mon, Jan 28, 2019 at 02:01:51PM -0600, Bin Liu wrote:
> > From: Paul Elder <paul.elder@ideasonboard.com>
> > 
> > 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@ideasonboard.com>
> > Signed-off-by: Bin Liu <b-liu@ti.com>
> 
> No "Fixes:" tag?

This patch changes the logic which was there in the very first commit of
the musb drivers more than a decade ago, so it seems the issue was there
from day one. I didn't add the 'Fixes:' tag, was thinking it doesn't add
any value.

Do you want me to add it?
	Fixes: 550a7375fe72 ("USB: Add MUSB and TUSB support")
> 
> No need for stable?

The patch might not be applied on stable cleanly. I was thinking to send
out backport patches for applicable stable trees once this patch got in
v5.0 -rc.

> 
> That seems odd...

Indeed, this is a forward-port from 2.6.34.

Regards,
-Bin.