linux-kernel - Re: [PATCH] usb: gadget: f_midi: Add checking if it need align buffer's size to an ep's maxpacketsize

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Date:	Fri, 08 Jul 2016 16:05:53 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Felipe Balbi <balbi@...nel.org>,
	Baolin Wang <baolin.wang@...aro.org>,
	Felipe Ferreri Tonello <eu@...ipetonello.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>, eu@...ipetonello.com,
	dan.carpenter@...cle.com, USB <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] usb: gadget: f_midi: Add checking if it need align buffer's size to an ep's maxpacketsize

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@...ipetonello.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@...a86.com>
>     Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
>     Signed-off-by: Felipe Balbi <felipe.balbi@...ux.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»