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

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Date:   Wed, 22 Jun 2022 23:31:05 +0200
From:   Stefan Berzl <stefanberzl@...il.com>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     benjamin.tissoires@...hat.com, spbnick@...il.com,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        José Expósito <jose.exposito89@...il.com>
Subject: Re: [PATCH] hid: Add support for the xp-pen deco mini7 tablet

Hello!

>> >From f9bb82e400effd3aea37b2be710add9e2bb832da Mon Sep 17 00:00:00 2001
>> From: Stefan Berzl <stefanberzl@...il.com>
>> Date: Fri, 11 Mar 2022 04:04:30 +0100
>> Subject: [PATCH] hid: Add support for the xp-pen deco mini7 tablet
>>
>> ...
> 
> Stefan,
> 
> sorry for not responding earlier, but this patch somehow fell in between 
> cracks. Please for your further submissions do not forget to at least CC 
> some of the relevant malinglists as well.

Will do... I am still new to the process and tend to forget things, but 
I'll do my best.

> Quite a lot has changed in uclogic driver since then, as José has been 
> pushing quite a lot of code there from DIGImend project ... could you 
> please update your patch on top of current codebase and resend it?
> 
> Thanks,
> 

I think you'll be pleased to find that José's work is basically a 
superset of mine, therefore eliminating the need for my patch 
altogether. When running his newest deco l code, the deco mini 7 is 
fully supported as well. I should have given a tested-by or something, 
but since I am still new to this, I was kinda hesitant with the big 
changes introduced by the newest digimend work. As you know, there is no 
sort of registry to differentiate devices by ability, so one or two
useless evdev devices are generated for hardware the tablet may or may 
not have, like "Touch Ring" or "Touch Strip". I thought that this might 
cause confusion and would have to be amended.

There is however one caveat that seems to be unique to the mini7, which 
is the ack packet that is sent when switching to the vendor defined 
usage. It doesn't do much though, as currently it gets interpreted as a 
pen report and since it doesn't have useful values, causes the cursor to 
go to the top left screen position. Since the ack packet is only sent 
once, it ought to be of little consequence.

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?
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?).

Everything said, I think this can be closed
https://patchwork.kernel.org/project/linux-input/patch/b401e453-9c66-15e3-1a1d-21f33b7a64e8@gmail.com/

Also I made this patch, which is very trivial and simplifies the hot path
https://patchwork.kernel.org/project/linux-input/patch/17153eb3-0eb9-cc05-4b65-9c0f4e8d3c90@gmail.com/

Thanks for your work on the linux input subsystem!

Kind Regards
Stefan Berzl

PS: notice how I put the right CCs and stuff :)