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

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Date:	Wed, 15 Sep 2010 13:56:41 +0300
From:	Felipe Balbi <balbi@...com>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Sergei Shtylyov <sshtylyov@...sta.com>,
	"Balbi, Felipe" <balbi@...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

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.

>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.

>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.

-- 
balbi
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