linux-kernel - Re: [RFC PATCH] usb: dwc3: ep0: Fix mem corruption on OUT transfers of more than 512 bytes

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Message-ID: <Pine.LNX.4.44L0.1506091320160.1324-100000@iolanthe.rowland.org>
Date:	Tue, 9 Jun 2015 13:24:32 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Kishon Vijay Abraham I <kishon@...com>
cc:	Michael Trimarchi <michael@...rulasolutions.com>,
	Felipe Balbi <balbi@...com>, <gregkh@...uxfoundation.org>,
	<linux-omap@...r.kernel.org>, <nsekhar@...com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [RFC PATCH] usb: dwc3: ep0: Fix mem corruption on OUT transfers
 of more than 512 bytes

On Tue, 9 Jun 2015, Kishon Vijay Abraham I wrote:

> > But with a bounce buffer that's only 512 bytes long, you can never send
> > an entire packet's worth of data.  If the bounce buffer is 1024 bytes
> 
> for control endpoint, 512 bytes should be sufficient to send entire packet right?

Yes, you're right.  I had confused control endpoints with bulk 
endpoints, where the maxpacket size is 1024.  Sorry for the mistake.

> > then you can send the entire first packet.  When that's done, you can
> > send the second packet.  And so on.  It wouldn't be quite as fast, but
> > for ep0 that shouldn't matter.
> 
> right! this is a variant of what I tried to implement in chained TRB [1]. 
> $subject tries just to avoid memory corruption instead of actually trying to 
> receive all the data.

Okay.  If you take the $SUBJECT approach, I think it would be better
for an URB submission to fail than for the host controller to send only
part of the data.

Alan Stern

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