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

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Date:	Fri, 1 Apr 2016 15:52:48 +0100
From:	Felipe Ferreri Tonello <eu@...ipetonello.com>
To:	Felipe Balbi <balbi@...nel.org>,
	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 Balbi,

On 01/04/16 11:22, Felipe Balbi wrote:
> 
> Hi,
> 
> Felipe Ferreri Tonello <eu@...ipetonello.com> writes:
>> Hi Balbi and Mina,
>>
>> 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?

So that means that buflen is still usable, at least on IN endpoints.

-- 
Felipe

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