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

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

[Geert Uytterhoeven]

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.

Fixes: b1442c55ce8977aa ("serial: 8250: extend compile-test coverage")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.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)
+	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"
-- 
2.25.1

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

[Johan Hovold]

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@glider.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

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

[Geert Uytterhoeven]

Hi Johan,

On Thu, Sep 16, 2021 at 10:46 AM Johan Hovold <johan@kernel.org> wrote:
> 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.

Getting it wrong would indeed be a regression, but not tightening
that at the same time would mean I have to send a separate patch with
a Fixes tag referring to this fix, following this template:

    foo should depend on bar

    The foo hardware is only present on bar SoCs.  Hence add a
    dependency on bar, to prevent asking the user about this driver
    when configuring a kernel without bar support.

> > Fixes: b1442c55ce8977aa ("serial: 8250: extend compile-test coverage")
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.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.

They are.

> 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"

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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

[Johan Hovold]

On Thu, Sep 16, 2021 at 10:55:49AM +0200, Geert Uytterhoeven wrote:
> Hi Johan,
> 
> On Thu, Sep 16, 2021 at 10:46 AM Johan Hovold <johan@kernel.org> wrote:
> > 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.
> 
> Getting it wrong would indeed be a regression, but not tightening
> that at the same time would mean I have to send a separate patch with
> a Fixes tag referring to this fix, following this template:
> 
>     foo should depend on bar
> 
>     The foo hardware is only present on bar SoCs.  Hence add a
>     dependency on bar, to prevent asking the user about this driver
>     when configuring a kernel without bar support.

I know this is a pet peeve of yours, but asking users about one more
symbol when configuring their kernels is hardly something that requires
a Fixes tag.

Either way it's a pretty weak argument for not separating the change.

Johan