linux-kernel - Re: [RESEND PATCH 1/2] HID: Add driver for RC Simulator Controllers

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Date:   Thu, 15 Sep 2022 09:34:06 +0200
From:   Marcus Folkesson <marcus.folkesson@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Jonathan Corbet <corbet@....net>, Jiri Kosina <jikos@...nel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "open list:HID CORE LAYER" <linux-input@...r.kernel.org>
Subject: Re: [RESEND PATCH 1/2] HID: Add driver for RC Simulator Controllers

Hi Benjamin,

On Tue, Aug 30, 2022 at 02:45:11PM +0200, Benjamin Tissoires wrote:
> On Thu, Aug 25, 2022 at 8:44 AM Marcus Folkesson
> <marcus.folkesson@...il.com> wrote:
> >


[...]
> >
> >
> > Is the fact that more than one button share the same
> > byte hard to describe in the report?
> 
> No, this is actually easy to describe. You say that there is one usage
> of "something" which has a report size of 1 bit, and then you have
> another usage of "something else" with the same report size.
> 
> But usually you have to add padding after to make up to 8 bits (so 6
> bits in that case).
> 
> I was referring to the case  where you are parsing the same bit on the
> wire, and give a different usage based if you have received an odd or
> an even number of reports. In that case, we probably need to use move
> this bit to a const field in the original report descriptor and say
> that the data is now not const:
> 
> - initial report (completely random example):
>   X (2 bytes) | Y (2 bytes) | button this_or_that (1 bit, depending of
> odd or even received reports) | 7 bits of padding
> - we can declare it as:
>   X (2 bytes) | Y (2 bytes) | button this (1 bit) | button that (1
> bit) | 6 bits of padding

How about if there is no unused bytes?

The XTRG2FMS has 8 10-bit channels and use every byte in the report.
Should I specify 8 8-bit channels instead and fix that in raw_event?
If so, should I only use 8bit values then?

(Are you at the ELCE conference btw?)

Best regards
Marcus Folkesson

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