linux-kernel - Re: [PATCH] usb: gadget: f_hid: optional SETUP/SET

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Message-ID: <20210814014518.GA56183@rowland.harvard.edu>
Date:   Fri, 13 Aug 2021 21:45:18 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Maxim Devaev <mdevaev@...il.com>
Cc:     balbi@...nel.org, gregkh@...uxfoundation.org,
        ruslan.bilovol@...il.com, mika.westerberg@...ux.intel.com,
        maze@...gle.com, jj251510319013@...il.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: f_hid: optional SETUP/SET_REPORT mode

On Fri, Aug 13, 2021 at 11:40:22PM +0300, Maxim Devaev wrote:
> В Fri, 13 Aug 2021 23:22:12 +0300
> Maxim Devaev <mdevaev@...il.com> пишет:
> 
> > Alan Stern <stern@...land.harvard.edu> wrote:
> > > In other words, a device does not need to have an interrupt-OUT 
> > > endpoint, but if it does have one then the host must use it.
> > 
> > You're right. Although the actual behavior of the hosts is not different
> > from what I wrote - they really just ignore out endpoint.
> > I will eventually fix this in the patch description.
> 
> It seems that I have confused everything even more, sorry. I will explain.
> There are three possible host behaviors:
> 
> (1) The host works with the OUT endpoint as it describes the standard
>     and transmits reports through it.
> 
> (2) The host works with IN endpoint, but refuses to transmit reports
>     via OUT endpoint at all. In the case of the keyboard, it will work,
>     but it will not receive the status of the LEDs.
> 
> (3) The host sees OUT endpoint and either refuses to use such a device at all,
>     or goes crazy in various ways.
> 
> In both cases (2) and (3), using SETUP/SET_REPORT solves the problem.
> Therefore, I offer this as an option to solve compatibility problems.
> Yes, in fact, this is not our problem, but it is impossible to fix the drivers
> of all these proprietary devices. Moreover, I have never met a keyboard
> with OUT endpoint, absolutely all of them use SETUP/SET_REPORT.

Okay.  I appreciate the more detailed explanations; thanks.  Please 
resubmit the patch with appropriate changes to the description.

Alan Stern