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

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Message-ID: <CACCg+XNdnzsn4RH+1OWJXNY6mVA9a6tpaUec3=P53WkywcWfkA@mail.gmail.com>
Date:   Wed, 17 Jun 2020 10:27:23 +0800
From:   Macpaul Lin <macpaul@...il.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Macpaul Lin <macpaul.lin@...iatek.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Sergey Organov <sorganov@...il.com>,
        Fabrice Gasnier <fabrice.gasnier@...com>,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Mediatek WSD Upstream <wsd_upstream@...iatek.com>,
        Macpaul Lin <macpaul.lin@...il.com>
Subject: Re: [PATCH 1/2] usb: gadget: introduce flag for large request

Alan Stern <stern@...land.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