linux-kernel - Re: [RESEND PATCH v8 06/10] serial: sc16is7xx: fix regression with GPIO configuration

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Date:   Fri, 21 Jul 2023 13:24:19 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Hugo Villeneuve <hugo@...ovil.com>
Cc:     gregkh@...uxfoundation.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, jirislaby@...nel.org, jringle@...dpoint.com,
        isaac.true@...onical.com, jesse.sung@...onical.com,
        tomasz.mon@...lingroup.com, l.perczak@...lintechnologies.com,
        linux-serial@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
        Hugo Villeneuve <hvilleneuve@...onoff.com>,
        stable@...r.kernel.org,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Lech Perczak <lech.perczak@...lingroup.com>
Subject: Re: [RESEND PATCH v8 06/10] serial: sc16is7xx: fix regression with
 GPIO configuration

On Fri, Jul 21, 2023 at 10:19 AM Hugo Villeneuve <hugo@...ovil.com> wrote:
>
> From: Hugo Villeneuve <hvilleneuve@...onoff.com>
>
> Commit 679875d1d880 ("sc16is7xx: Separate GPIOs from modem control lines")
> and commit 21144bab4f11 ("sc16is7xx: Handle modem status lines")
> changed the function of the GPIOs pins to act as modem control
> lines without any possibility of selecting GPIO function.

Requiring a new DT property is not fixing a kernel regression. You
should be returning the kernel to original behavior and then have a
new DT property for new behavior.

> As a consequence, applications that depends on GPIO lines configured
> by default as GPIO pins no longer work as expected.
>
> Also, the change to select modem control lines function was done only
> for channel A of dual UART variants (752/762). This was not documented
> in the log message.
>
> Allow to specify GPIO or modem control line function in the device
> tree, and for each of the ports (A or B).
>
> Do so by using the new device-tree property named
> "modem-control-line-ports" (property added in separate patch).

That's not the name in the patch.

> When registering GPIO chip controller, mask-out GPIO pins declared as
> modem control lines according to this new "modem-control-line-ports"
> DT property.
>
> Boards that need to have GPIOS configured as modem control lines
> should add that property to their device tree. Here is a list of
> boards using the sc16is7xx driver in their device tree and that may
> need to be modified:
>     arm64/boot/dts/freescale/fsl-ls1012a-frdm.dts
>     mips/boot/dts/ingenic/cu1830-neo.dts
>     mips/boot/dts/ingenic/cu1000-neo.dts

Then again, if no one cares about those boards needing a change then
it can be okay.


Rob