linux-kernel - Re: [PATCH] hid: Add support for the xp-pen deco mini7 tablet

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Date:   Thu, 23 Jun 2022 21:01:41 +0300
From:   Nikolai Kondrashov <spbnick@...il.com>
To:     José Expósito <jose.exposito89@...il.com>,
        Stefan Berzl <stefanberzl@...il.com>
Cc:     Jiri Kosina <jikos@...nel.org>, benjamin.tissoires@...hat.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hid: Add support for the xp-pen deco mini7 tablet

On 6/23/22 20:51, José Expósito wrote:
>> I would of course fix this, but I don't really know what's the preferred
>> way. One can obviously simply set up an urb to catch this, but it would
>> have to be a special corner case for the mini 7, as José assures me that
>> none of his tablets display similar behavior. Is this acceptable?
> 
> My tablets also send an ACK packet, but in my case it does not have any
> visible effects. Maybe it is related to the DE environment used. I
> tested it on elementary OS (Ubuntu) and Fedora 36, in both cases the
> ACK is ignored... But catching it is fine, we can include the code you
> suggest.
> 
>> José already had a look at some firmware device descriptor string that
>> reports the number of buttons and what not, but as far as I know, it
>> doesn't say anything about ack packets (right José? Does it say
>> anything about touch strips or similar?).
> 
> In the devices I tested, the ACK packet is always present, so it should
> be fine to catch it. I'll test your patch in all the devices I own to
> be safe.

I think it's OK to just ignore the first packet for these devices, even if the 
ACK packet is not sent for some of them. Even with the report rate of 20 years 
ago nobody would've noticed if you dropped one packet.

Nick