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 17:02:45 +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

Felipe Balbi wrote:

>>> your forgetting the fact that not always you need to send ZLP after
>>> completing a packet_size-aligned transfer,

>>    So what?

> what you're saying is that when we change the ZLP handling, the
> request->actual == request->lenght check will have to be removed, but
> that's not true because ZLP is only needed if request->zero is set.

> So the final code would be something like (pseudo-code):

> if (request->lenght % musb_ep->packet_sz)
>     set_last_packet_is_short_flag(musb_request);

> if (request->zero || last_packet_is_short(request)) {
>     set_txpktrdy(musb);
>     set_musb_request_completed_flag(musb_request);
>     return;
> }

> if (request->acual == request->length)
>     musb_g_giveback(musb, request);

> restart_ep_if_more_requests(musb_ep);

    No, this code will still send ZLP before the whole requested transfer is 
done. The (request->actual == request->length) check is needed before we even 
check that request->zero is set (and it is there but not for the DMA case). I 
thought that this was quite obvious, and I was surprised that this caused such a 
lengthy discussion.

WBR, Sergei
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