linux-kernel - Re: [PATCH 1/2] usb: gadget: f

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Message-ID: <567A8A77.4000504@felipetonello.com>
Date:	Wed, 23 Dec 2015 11:50:15 +0000
From:	Felipe Ferreri Tonello <eu@...ipetonello.com>
To:	Clemens Ladisch <clemens@...isch.de>, linux-usb@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Robert Baldyga <r.baldyga@...sung.com>
Subject: Re: [PATCH 1/2] usb: gadget: f_midi: refactor state machine

Hi Clemens,

On 22/12/15 17:10, Clemens Ladisch wrote:
> Felipe F. Tonello wrote:
>> This refactor includes the following:
>>  * Cleaner state machine code;
> 
> It does not correctly handle system real time messages inserted between
> the status and data bytes of other messages.

True, thanks for pointing that out. I fixed that on next revision of
this patch.

> 
>>  * Reset state if MIDI message parsed is non-conformant;
> 
> Why?  In a byte stream like "C1 C3 44", where the data byte of the first
> message was lost, the reset would also drop the second message.

True. That was fixed as well.

> 
>>  * Fixed bug when a conformant MIDI message was followed by a non-conformant
>>    causing the MIDI-USB message to use old temporary data (port->data[0..1]),
>>    thus packing a wrong MIDI-USB request.
> 
> Running status is feature.

What do you mean by that? I don't qualify writing a *wrong* MIDI-USB
packet because of a previous MIDI message as a feature.

For instance, try this MIDI message:
"8A 54 24 00 40"

It will be converted to MIDI-USB as "08 8A 54 24 08 8A 00 40" which is
wrong. It should only be "08 8A 54 24" and ignore the "00 40" MIDI bytes.

On every state byte the message should basically reset data[0..1] to
zero overwriting previous data. This should also be true when a MIDI-USB
packet is complete.

Felipe

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