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

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Message-ID: <20100915065345.GC3393@legolas.emea.dhcp.ti.com>
Date:	Wed, 15 Sep 2010 09:53:45 +0300
From:	Felipe Balbi <balbi@...com>
To:	Sergei Shtylyov <sshtylyov@...sta.com>
Cc:	"Balbi, Felipe" <balbi@...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

On Tue, Sep 14, 2010 at 12:51:09PM -0500, Sergei Shtylyov wrote:
>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.

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,...);

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

>> 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.

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.

-- 
balbi
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