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From:   Macpaul Lin <macpaul@gmail.com>
Date:   Wed, 17 Jun 2020 10:27:23 +0800
Message-ID: <CACCg+XNdnzsn4RH+1OWJXNY6mVA9a6tpaUec3=P53WkywcWfkA@mail.gmail.com>
Subject: Re: [PATCH 1/2] usb: gadget: introduce flag for large request
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>,
        =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <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>
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Alan Stern <stern@rowland.harvard.edu> =E6=96=BC 2020=E5=B9=B46=E6=9C=8816=
=E6=97=A5 =E9=80=B1=E4=BA=8C =E4=B8=8B=E5=8D=8810:05=E5=AF=AB=E9=81=93=EF=
=BC=9A
>
> 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 siz=
e
> > 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 pack=
et.
Isn't there any historical reason?

--=20
Best regards,
Macpaul Lin