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

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Date:	Wed, 10 Jun 2015 11:03:59 +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 10:54 PM, Alan Stern wrote:
> 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.

no problem.
>
>>> 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.

Could be but we also want to prevent mem corruption in the case of a faulty 
host to be more robust.

Thanks
Kishon
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