Re: [PATCH 1/2] usb: gadget: introduce flag for large request

From: Macpaul Lin <macpaul@gmail.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: "Macpaul Lin" <macpaul.lin@mediatek.com>,
	"Chunfeng Yun" <chunfeng.yun@mediatek.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Felipe Balbi" <balbi@kernel.org>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
	"Sergey Organov" <sorganov@gmail.com>,
	"Fabrice Gasnier" <fabrice.gasnier@st.com>,
	linux-usb@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org,
	"Mediatek WSD Upstream" <wsd_upstream@mediatek.com>,
	"Macpaul Lin" <macpaul.lin@gmail.com>
Subject: Re: [PATCH 1/2] usb: gadget: introduce flag for large request
Date: Wed, 17 Jun 2020 10:27:23 +0800	[thread overview]
Message-ID: <CACCg+XNdnzsn4RH+1OWJXNY6mVA9a6tpaUec3=P53WkywcWfkA@mail.gmail.com> (raw)
In-Reply-To: <20200616140246.GA30975@rowland.harvard.edu>

Alan Stern <stern@rowland.harvard.edu> 於 2020年6月16日 週二 下午10:05寫道：
>
> On Tue, Jun 16, 2020 at 08:34:43PM +0800, Macpaul Lin wrote:
> > Some USB hardware like DMA engine can help to process (split) the data
> > of each URB request into small packets. For example, the max packet size
> > of high speed is 512 bytes. These kinds of hardware can help to split
> > the continue Tx/Rx data requests into packets just at the max packet
> > size during transmission. Hence upper layer software can reduce some
> > effort for queueing many requests back and forth for larger data.
> >
> > Here we introduce "can_exceed_maxp" flag in gadget when these kinds of
> > hardware is ready to support these operations.
>
> This isn't needed.  All UDC drivers must be able to support requests that
> are larger than the maxpacket size.
>
> Alan Stern

Thanks for your reply, could we just modify the patch 2 (u_serial.c)
for improving
better performance? I'm not sure why there was a restriction about max packet.
Isn't there any historical reason?

-- 
Best regards,
Macpaul Lin