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

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Date:	Wed, 15 Sep 2010 14:01:05 +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.

On 15-09-2010 10:53, 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.

> When I said 'whole transfer' I meant the transfer size you programmed
> dma to transfer, see that we have (not actual code):

> if (transfer_size > dma->max_len)
> transfer_size = dma->max_len;

> dma->channel_program(...,..., transfer_size,...);

    Ah, I didn't mean the same thing -- I meant the transfer size as specified 
by 'struct usb_request'.

> with mode1, we will only get irq when dma has transferred transfer_size
> bytes.

    Sure.

>>> 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?

> if request->length == 1MB and dma->max_len = 128KB, when is_dma is true,
> request->actual will be different from request->length for 7
> 'iterations', then only on the 8th it will be the same. I believe that's
> what Ming is trying to fix.

    I repeat once again: it's too late to check this where Ming is inserting 
the check.

> Ming, am I correct ?
>
>> Let me repeat: in the PIO mode the added check is just duplicate, in the DMA

> it is duplicate for PIO, but not for DMA.

    I didn't say it was duplicate for DMA, just too late.

WBR, Sergei
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