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SubjectRe: [PATCH v2] usb: gadget: musb: fix short isoc packets with inventra dma
Hi Paul,

On Wed, Jan 09, 2019 at 02:10:09AM -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@ideasonboard.com>
> ---
> 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 | 19 +++++--------------
> drivers/usb/musb/musbhsdma.c | 21 +++++++++++----------
> 2 files changed, 16 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/usb/musb/musb_gadget.c b/drivers/usb/musb/musb_gadget.c
> index eae8b1b1b45b..496643f54faa 100644
> --- a/drivers/usb/musb/musb_gadget.c
> +++ b/drivers/usb/musb/musb_gadget.c
> @@ -452,13 +452,10 @@ void musb_g_tx(struct musb *musb, u8 epnum)
> }
>
> if (request) {
> - u8 is_dma = 0;
> - bool short_packet = false;
>
> trace_musb_req_tx(req);
>
> if (dma && (csr & MUSB_TXCSR_DMAENAB)) {
> - is_dma = 1;
> csr |= MUSB_TXCSR_P_WZC_BITS;
> csr &= ~(MUSB_TXCSR_DMAENAB | MUSB_TXCSR_P_UNDERRUN |
> MUSB_TXCSR_TXPKTRDY | MUSB_TXCSR_AUTOSET);
> @@ -476,16 +473,8 @@ void musb_g_tx(struct musb *musb, u8 epnum)
> */
> if ((request->zero && request->length)
> && (request->length % musb_ep->packet_sz == 0)
> - && (request->actual == request->length))
> - short_packet = true;
> + && (request->actual == request->length)) {
>
> - if ((musb_dma_inventra(musb) || musb_dma_ux500(musb)) &&
> - (is_dma && (!dma->desired_mode ||
> - (request->actual &
> - (musb_ep->packet_sz - 1)))))
> - short_packet = true;
> -
> - if (short_packet) {
> /*
> * On DMA completion, FIFO may not be
> * available yet...
> @@ -493,8 +482,10 @@ void musb_g_tx(struct musb *musb, u8 epnum)
> if (csr & MUSB_TXCSR_TXPKTRDY)
> return;
>
> - musb_writew(epio, MUSB_TXCSR, MUSB_TXCSR_MODE
> - | MUSB_TXCSR_TXPKTRDY);
> + musb_dbg(musb, "sending short pkt (zero=%d, length=%d, actual=%d, dma->desired_mode=%d)\n",
> + request->zero, request->length, request->actual,
> + dma->desired_mode);
> + musb_writew(epio, MUSB_TXCSR, csr | MUSB_TXCSR_TXPKTRDY);

Sorry I didn't catch this in the last review, but this change seems not
required, isn't it? In the first version of the patch, the code is
'returned' in the 'if (musb_dma_inventra())' branch above, doesn't reach
here.

Regards,
-Bin.

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