linux-kernel - Re: [Discussion] USB: musb-gadget: how to fix ZLP issue in musb_g

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Message-ID: <AANLkTi=gYSsxSHqAur+isj_UinVLC-YWkdmi5j_vkSUV@mail.gmail.com>
Date:	Wed, 15 Sep 2010 19:02:22 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	balbi@...com
Cc:	Sergei Shtylyov <sshtylyov@...sta.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: [Discussion] USB: musb-gadget: how to fix ZLP issue in musb_g_tx

2010/9/15 Felipe Balbi <balbi@...com>:
> Hi,
>
> On Wed, Sep 15, 2010 at 05:53:10AM -0500, Ming Lei wrote:
>>
>> 1),  why is the check for "is_dma" needed here?
>>
>>     if (is_dma || request->actual == request->length) {
>>          ....
>>     }
>
> if you programmed dma to request->length (and assuming it worked just
> fine) mode1 will only interrupt you when the entire request has been
> sent.

If so, once the dma interrupt comes, will request->actual be same
with request->length in musb_g_tx?  And if it is true, could we remove the
check for 'is_dma'?

>
>> 2), why is a zlp needed in the case below?
>>
>>     #ifdef CONFIG_USB_INVENTRA_DMA
>>                 || (is_dma && (!dma->desired_mode ||
>>                    (request->actual & (musb_ep->packet_sz - 1))))
>>    #endif
>
> in that case, it's not a zlp, it's short packet. Inventra will *NOT*
> transfer short packets, you need to set txpktrdy by hand to get it
> transfered.

I see now.

>
>> IMO, it is not difficult to give a good fix for the ZLP problem
>> if the two questions are clear.
>
> true, but some re-work needs to be done.

Thanks for your reply.


-- 
Lei Ming
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