linux-kernel - Re: [PATCH 2/5] Input: add driver for Focaltech FTS touchscreen

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Date:   Sun, 9 Apr 2023 16:32:27 +0300
From:   Markuss Broks <markuss.broks@...il.com>
To:     Joel Selvaraj <joelselvaraj.oss@...il.com>,
        Caleb Connolly <caleb@...nolly.tech>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Henrik Rydberg <rydberg@...math.org>,
        Arnd Bergmann <arnd@...db.de>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Jeff LaBundy <jeff@...undy.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Jean Delvare <jdelvare@...e.de>,
        Max Krummenacher <max.krummenacher@...adex.com>,
        Job Noorman <job@...rman.info>,
        Alistair Francis <alistair@...stair23.me>,
        Chris Morgan <macromorgan@...mail.com>
Cc:     linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org
Subject: Re: [PATCH 2/5] Input: add driver for Focaltech FTS touchscreen

Hi Joel,

Sorry for responding late:

On 3/13/23 00:21, Joel Selvaraj wrote:
> Hi Markuss,
>
> Thanks for the quick review! I agree with most of your comments and will
> fix them in a v2 soon. I have a few doubts as discussed below.
>
> On 12/03/23 15:40, Markuss Broks wrote:
>
>> Why is the _ratelimited variant necessary?
> I assumed in case of the interrupt working, but i2c reads fail for some
> reason, it would spam a lot of error messages if the user touches the
> screen continuously, like a swipe up gesture or something.
>
> I referred to ad7879 touchscreen's irq handling code [1] and thought
> it's probably best to do this, to be on the safe side. I will remove
> this if it's not needed in v2.
>
>> Overall, I think it's better to cast the data type to a struct, which
>> would make this seem with less random.
> Sorry, I am not sure I got this right. Do you mean I create an array of
> struct called say "fts_point" that stores the x, y, type, etc. info of
> all the points, then report it separately. Like similar to something
> done by the auo-pixcir touchscreen driver [2]?

By that I meant doing something like the Zinitix driver[1] does. It has 
a struct data type for whatever you read from hardware, e.g.

struct point_coord {
     __le16    x;
     __le16    y;
...
};

from that driver. That way you can cast the data read to that struct and 
have it look a bit nicer.

This is just a suggestion though, you have the final choice in what 
design you choose for your code :)

>
> If I didn't get this correctly, can you show me some code in mainline,
> that does it? It would be very helpful.
>
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/input/touchscreen/ad7879.c?h=v6.3-rc1#n250
> [2]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/input/touchscreen/auo-pixcir-ts.c?h=v6.3-rc1#n162
>
>> - Markuss
> Thanks,
> Joel
[1]
https://elixir.free-electrons.com/linux/v6.3-rc5/source/drivers/input/touchscreen/zinitix.c


- Markuss