linux-kernel - Re: [PATCH] usb: raw-gadget: fix gadget endpoint selection

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Message-ID: <Pine.LNX.4.44L0.2004282110170.26482-100000@netrider.rowland.org>
Date:   Tue, 28 Apr 2020 21:14:34 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Andrey Konovalov <andreyknvl@...gle.com>
cc:     USB list <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: raw-gadget: fix gadget endpoint selection

On Tue, 28 Apr 2020, Andrey Konovalov wrote:

> Hi Alan,
> 
> This patch uses the approach that I mentioned in the discussion about
> endpoint selection. Does this look acceptable?

I haven't had time to look through it yet.

> I'm not sure which endpoint limits it makes sense to expose via
> USB_RAW_IOCTL_EPS_INFO. I'm more or less sure about maxpacket_limit
> and max_streams, but I don't exactly know what maxburst is used for.
> Maybe there are some others?

maxburst is a USB-3 thing.  It mainly affects just throughput, not 
functionality, and it's handled pretty much entirely by the hardware.  
You shouldn't worry about it, at least, not now.

> I also wonder if we need to expose ep0 limits via USB_RAW_IOCTL_EPS_INFO too.
> expose ep0 parameters?

I don't think there are any significant attributes for ep0.  In
general, gadget drivers have to live with what the hardware supports --
or else fail to run at all.  After all, the driver can't substitute a 
different endpoint for ep0.

Alan Stern