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

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Date:	Mon, 04 Apr 2016 13:46:21 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Felipe Ferreri Tonello <eu@...ipetonello.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	linux-usb@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Robert Baldyga <r.baldyga@...sung.com>
Subject: Re: [PATCH] usb: gadget: f_midi: Fixed a bug when buflen was smaller than wMaxPacketSize


Hi,

Felipe Ferreri Tonello <eu@...ipetonello.com> writes:
>>> On 30/03/16 13:33, Michal Nazarewicz wrote:
>>>> On Wed, Mar 30 2016, Felipe Balbi wrote:
>>>>> a USB packet, right. that's correct. But a struct usb_request can
>>>>> point to whatever size buffer it wants and UDC is required to split
>>>>> that into wMaxPacketSize transfers.
>>>>
>>>> D’oh.  Of course.  Disregard all my comments on the patch (except for
>>>> Ack).
>>>>
>>>
>>> I didn't really get it. Does that mean that if buflen is multiple of
>>> wMaxPacketSize, the UDC driver should fit as many [DATA] packets into
>>> one usb_request and call complete() or it will always call complete() on
>>> each [DATA] packet, thus not requiring buflen at all?
>>>
>>> Does that mean that we can still use buflen and this patch is still
>>> valid? (besides the endianess issue that was addressed on v2)
>> 
>> if you have e.g. 2048 bytes of data to transfer and wMaxPacketSize is
>> e.g. 256 bytes, the UDC controller is required to do whatever it needs
>> to do to transfer 2048 bytes (or less if there's a short packet).
>> 
>> You don't need to break these 2048 bytes into several requests yourself,
>> the UDC is required to do that for the gadget.
>
> Right, what about OUT endpoints?

also applicable

-- 
balbi

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