linux-kernel - Re: [PATCH v2] char: xillybus: Check endpoint type before allocing

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Date:   Thu, 26 May 2022 20:02:28 +0800
From:   Zheyu Ma <zheyuma97@...il.com>
To:     Eli Billauer <eli.billauer@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, arnd@...db.de,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] char: xillybus: Check endpoint type before allocing

On Tue, May 24, 2022 at 8:24 PM Eli Billauer <eli.billauer@...il.com> wrote:
>
> On 23/05/22 20:15, Greg KH wrote:
> >> Rather, it works like this: The driver uses the EP 1 IN and OUT endpoints to
> >> >  query the device for a data structure, which contains information on the
> >> >  device's communication channels. The driver sets up device files
> >> >  accordingly, and it also gets informed on which bulk OUT endpoints are
> >> >  present.
> >> >
> >> >  For what it's worth, I think it's fairly safe to assume that if a device
> >> >  returns a legal data structure (which passes a CRC test), it's a XillyUSB
> >> >  device.
> >>
> > Why?  You still need to verify that the requested endpoints match up
> > with what the device really has.
> >
> OK. So to summarize:
>
> EP 1 IN and EP 1 OUT are always present in XillyUSB devices.
>
> On top of these, there might be additional bulk OUT endpoints. The
> driver resolves which ones in setup_channels(), by scanning a data blob
> it has received from the device. This takes place in the for-loop inside
> this function. When (out_desc & 0x80) is true for a given @i in the
> loop, the device has a bulk OUT endpoint with address i+2 (e.g. if this
> condition is met for i==2, the device has a bulk OUT EP 4).
>
> So it seems like setup_channels() would be the right place to make this
> check, since it's called during the device's probe.
>
> I guess it would likewise make sense to check for EP 1 IN and OUT in
> xillyusb_setup_base_eps().
>
> Thanks,
>     Eli

Thanks for the detailed explanation, I will try to send a new version
of the patch to fix the bug.

Thanks,
Zheyu Ma