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

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Message-ID: <20200616140246.GA30975@rowland.harvard.edu>
Date:   Tue, 16 Jun 2020 10:02:46 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Macpaul Lin <macpaul.lin@...iatek.com>
Cc:     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

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