linux-kernel - Re: [PATCH v2] usb: gadget: f_midi: fixed a bug when buflen was smaller than wMaxPacketSize

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Message-ID: <87lh51shmm.fsf@intel.com>
Date:	Tue, 29 Mar 2016 13:28:17 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	"Felipe F. Tonello" <eu@...ipetonello.com>,
	linux-usb@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Clemens Ladisch <clemens@...isch.de>
Subject: Re: [PATCH v2] usb: gadget: f_midi: fixed a bug when buflen was smaller than wMaxPacketSize


Hi,

"Felipe F. Tonello" <eu@...ipetonello.com> writes:
> [ text/plain ]
> 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]
>
> Users should not change the buffer size to anything other than wMaxPacketSize
> because that can cause bugs (this bug) or performance issues. Thus, this patch
> fixes this problem by eliminating buflen entirely and replacing it with
> wMaxPacketSize of the appropriate endpoint where needed.
>
> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
> ---
>
> v2:
>  - Removed buflen

sounds like removing buflen should be delyed to v4.7 merge window while
the fix is, indeed, needed. Can you drop the removal of buflen ? I guess
it's mostly about picking v1 and fixing endianess problems ?

-- 
balbi

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