linux-kernel - Re: [PATCH] serial: 8250: SERIAL_8250_FSL should not default to y when compile-testing

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Message-ID: <YUMESxr907YHM3ZT@hovoldconsulting.com>
Date:   Thu, 16 Sep 2021 10:46:03 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>, Li Yang <leoyang.li@....com>,
        Scott Wood <oss@...error.net>, linux-serial@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: 8250: SERIAL_8250_FSL should not default to y
 when compile-testing

On Wed, Sep 15, 2021 at 02:56:52PM +0200, Geert Uytterhoeven wrote:
> Commit b1442c55ce8977aa ("serial: 8250: extend compile-test coverage")
> added compile-test support to the Freescale 16550 driver.  However, as
> SERIAL_8250_FSL is an invisible symbol, merely enabling COMPILE_TEST now
> enables this driver.
> 
> Fix this by making SERIAL_8250_FSL visible.  Tighten the dependencies to
> prevent asking the user about this driver when configuring a kernel
> without appropriate Freescale SoC or ACPI support.

This tightening is arguable a separate change which risk introducing
regressions if you get it wrong and should go in a separate patch at
least.

> Fixes: b1442c55ce8977aa ("serial: 8250: extend compile-test coverage")
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> Yes, it's ugly, but I see no better solution. Do you?
> 
>  drivers/tty/serial/8250/Kconfig | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> index 808268edd2e82a45..a2978b31144e94f2 100644
> --- a/drivers/tty/serial/8250/Kconfig
> +++ b/drivers/tty/serial/8250/Kconfig
> @@ -361,9 +361,13 @@ config SERIAL_8250_BCM2835AUX
>  	  If unsure, say N.
>  
>  config SERIAL_8250_FSL
> -	bool
> +	bool "Freescale 16550-style UART support (8250 based driver)"
>  	depends on SERIAL_8250_CONSOLE
> -	default PPC || ARM || ARM64 || COMPILE_TEST
> +	depends on FSL_SOC || ARCH_LAYERSCAPE || SOC_LS1021A || (ARM64 && ACPI) || COMPILE_TEST
> +	default FSL_SOC || ARCH_LAYERSCAPE || SOC_LS1021A || (ARM64 && ACPI)

I'd suggest just doing

	bool "Freescale 16550-style UART support (8250 based driver)"
	depends on SERIAL_8250_CONSOLE
	default PPC || ARM || ARM64

Since neither of the symbols you add to that "depends on" line is an
actual build or runtime dependency.

Then you can refine the "default" line in a follow up (or argue why you
think there should be a "depends on FSL_SOC || ...").

> +	help
> +	  Selecting this option will add support for the 16550-style serial
> +	  port hardware found on Freescale SoCs.
>  
>  config SERIAL_8250_DW
>  	tristate "Support for Synopsys DesignWare 8250 quirks"

Johan