linux-kernel - Re: [RESEND/PATCH 5/6] USB: musb-gadget: complete request only if data is transfered over

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Message-ID: <4C8FB60D.1080906@ru.mvista.com>
Date:	Tue, 14 Sep 2010 21:51:09 +0400
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	balbi@...com
CC:	Sergei Shtylyov <sshtylyov@...sta.com>,
	Ming Lei <tom.leiming@...il.com>,
	"greg@...ah.com" <greg@...ah.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	"Gadiyar, Anand" <gadiyar@...com>,
	Mike Frysinger <vapier@...too.org>
Subject: Re: [RESEND/PATCH 5/6] USB: musb-gadget: complete request only if
 data is transfered over

Hello.

Felipe Balbi wrote:

>>    If a DMA interrupt comes when the whole transfer is not yet 
>> complete (and
>> other Ming Lei's patches are making this possible),

    Oh, here I mixed some other patch with Ming Lei's ones...

>> it will pass due to the

> than this is the actual problem, no ? If we're using mode1 dma (as we
> are on tx path), we should only get dma interrupt when the whole
> transfer has been completed.

    The Inventra DMA controller has serious DMA length limitation, so the whole 
transfer may take more than one DMA.

>> 'ís_dma' condition above the patched code:

>>                 if (is_dma || request->actual == request->length) {

>> and then it will hit the code sending the final ZLP (above this 
>> patched code too):

> but this was already there before the patch.

    Yes, and here lies the problem.

>>                         /*
>>                          * First, maybe a terminating short packet. 
>> Some DMA
>>                          * engines might handle this by themselves.
>>                          */
>>                         if ((request->zero && request->length
>>                                 && request->length % 
>> musb_ep->packet_sz == 0)
>> #ifdef CONFIG_USB_INVENTRA_DMA
>>                                 || (is_dma && (!dma->desired_mode ||
>>                                         (request->actual &
>>                                                 (musb_ep->packet_sz - 
>> 1))))
>> #endif
>>                         ) {

>> before the transfer is complete while it should only be hit when and 
>> only when
>> the whole transfer is complete. The current code doesn't look correct 
>> as well
>> though, all due to this 'ís_dma' condition. Surely this needs fixing.

> likewise, this was there before the patch. I don't think the real
> problem lies with this patch, it's been there for a while, don't you
> agree ?

    Then what problem this patch fixes, if not this one?

> the problem is not on the extra if () added below the quoted code,
> it's on the quoted code itself, which wasn't changed in any way.

    Let me repeat: in the PIO mode the added check is just duplicate, in the DMA 
mode it's added too late in the code, after ZLP/short packet send is triggered.
We should modify the check at the top of that code instead.

WBR, Sergei
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