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

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Date:	Tue, 9 Jun 2015 21:44:06 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Alan Stern <stern@...land.harvard.edu>
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

Hi,

On Tuesday 09 June 2015 08:46 PM, Alan Stern wrote:
> On Tue, 9 Jun 2015, Kishon Vijay Abraham I wrote:
>
>>> Why not just make the bounce buffer size the same as the maxpacket
>>> size?  In other words, 1024 bytes instead of 512, for ep0 on a USB-3
>>> device.
>>
>> It would still be possible for the host to send data more than 1024 bytes no?
>
> Yes.
>
>> When working with DFU gadget, I've seen host sends data upto 4KB. Changing the
>> bounce buffer size might not be able to fix all the cases IMO. The actual fix
>> will be something like [1]
>>
>> [1] -> http://comments.gmane.org/gmane.linux.kernel/1883688
>
> 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?
> 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.

Thanks
Kishon
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