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SubjectRe: [PATCH] usb: gadget: f_midi: Add checking if it need align buffer's size to an ep's maxpacketsize
Date
On Fri, Jul 08 2016, Felipe Balbi wrote:
> My take on this is that it's calling max_t() to try and align to
> wMaxPacketSize. We can see from original commit what was the intent:
>
> commit 03d27ade4941076b34c823d63d91dc895731a595
> Author: Felipe F. Tonello <eu@felipetonello.com>
> Date: Wed Mar 9 19:39:30 2016 +0000
>
> usb: gadget: f_midi: Fixed a bug when buflen was smaller than wMaxPacketSize
>
> buflen by default (256) is smaller than wMaxPacketSize (512) in high-speed
> devices.
>
> That caused the OUT endpoint to freeze if the host send any data packet of
> length greater than 256 bytes.
>
> This is an example dump of what happended on that enpoint:
> HOST: [DATA][Length=260][...]
> DEVICE: [NAK]
> HOST: [PING]
> DEVICE: [NAK]
> HOST: [PING]
> DEVICE: [NAK]
> ...
> HOST: [PING]
> DEVICE: [NAK]
>
> This patch fixes this problem by setting the minimum usb_request's buffer size
> for the OUT endpoint as its wMaxPacketSize.
>
> Acked-by: Michal Nazarewicz <mina86@mina86.com>
> Signed-off-by: Felipe F. Tonello <eu@felipetonello.com>
> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
>
> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
> index 56e2dde99b03..9ad51dcab982 100644
> --- a/drivers/usb/gadget/function/f_midi.c
> +++ b/drivers/usb/gadget/function/f_midi.c
> @@ -360,7 +360,9 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
> /* allocate a bunch of read buffers and queue them all at once. */
> for (i = 0; i < midi->qlen && err == 0; i++) {
> struct usb_request *req =
> - midi_alloc_ep_req(midi->out_ep, midi->buflen);
> + midi_alloc_ep_req(midi->out_ep,
> + max_t(unsigned, midi->buflen,
> + bulk_out_desc.wMaxPacketSize));
> if (req == NULL)
> return -ENOMEM;
>
> Seems to me usb_ep_align_maybe() would cover this case just as well. But
> then, Felipe's UDC driver seems to need quirk_ep_out_aligned_size. Felipe?

In that case, I agree that max is likely unnecessary.

--
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»

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