linux-kernel - Re: [PATCH v3 2/2] serial: 8250: Apply FSL workarounds also without SERIAL_8250

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Message-ID: <20230605142225.75l6px3ep5ythkl6@pengutronix.de>
Date:   Mon, 5 Jun 2023 16:22:25 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Tharun Kumar P <tharunkumar.pasumarthi@...rochip.com>,
        kernel@...gutronix.de,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Randy Dunlap <rdunlap@...radead.org>,
        linuxppc-dev@...ts.ozlabs.org, Nicholas Piggin <npiggin@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Kumaravel Thiagarajan <kumaravel.thiagarajan@...rochip.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-serial <linux-serial@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Matthew Gerlach <matthew.gerlach@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Liang He <windhl@....com>
Subject: Re: [PATCH v3 2/2] serial: 8250: Apply FSL workarounds also without
 SERIAL_8250_CONSOLE

Hello Ilpo,

On Mon, Jun 05, 2023 at 04:44:08PM +0300, Ilpo Järvinen wrote:
> On Mon, 5 Jun 2023, Uwe Kleine-König wrote:
> > On Mon, Jun 05, 2023 at 04:22:55PM +0300, Ilpo Järvinen wrote:
> > > On Mon, 5 Jun 2023, Uwe Kleine-König wrote:
> > > 
> > > > The need to handle the FSL variant of 8250 in a special way is also
> > > > present without console support. So soften the dependency for
> > > > SERIAL_8250_FSL accordingly. Note that with the 8250 driver compiled as
> > > > a module, some devices still might not make use of the needed
> > > > workarounds. That affects the ports instantiated in
> > > > arch/powerpc/kernel/legacy_serial.c.
> > > > 
> > > > This issue was identified by Dominik Andreas Schorpp.
> > > > 
> > > > To cope for CONFIG_SERIAL_8250=m + CONFIG_SERIAL_8250_FSL=y, 8250_fsl.o
> > > > must be put in the same compilation unit as 8250_port.o because the
> > > > latter defines some functions needed in the former and so 8250_fsl.o
> > > > must not be built-in if 8250_port.o is available in a module.
> > > > 
> > > > Acked-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > > > Link: https://lore.kernel.org/r/20230531083230.2702181-1-u.kleine-koenig@pengutronix.de
> > > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > > ---
> > > >  drivers/tty/serial/8250/Kconfig  | 2 +-
> > > >  drivers/tty/serial/8250/Makefile | 2 +-
> > > >  2 files changed, 2 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
> > > > index 5313aa31930f..10c09b19c871 100644
> > > > --- a/drivers/tty/serial/8250/Kconfig
> > > > +++ b/drivers/tty/serial/8250/Kconfig
> > > > @@ -378,7 +378,7 @@ config SERIAL_8250_BCM2835AUX
> > > >  
> > > >  config SERIAL_8250_FSL
> > > >  	bool "Freescale 16550 UART support" if COMPILE_TEST && !(PPC || ARM || ARM64)
> > > > -	depends on SERIAL_8250_CONSOLE
> > > > +	depends on SERIAL_8250
> > > 
> > > Just one additional thought: After the adding the arch side 
> > > workaround/hack, SERIAL_8250_FSL could become a tristate?
> > 
> > I see no benefit for a module separate from 8250_base.ko. There are
> > dependencies in both directions between 8250_port.o and 8250_fsl.o[1].
> > So in my book a bool SERIAL_8250_FSL that modifies 8250_base.ko (with
> > SERIAL_8250=m) is fine.
> > 
> > Best regards
> > Uwe
> > 
> > [1] 8250_port.o uses fsl8250_handle_irq() from 8250_fsl.o
> 
> Is that after some fix which isn't in tty-next? I see only these:
> 
> $ git grep -l fsl8250_handle_irq
> arch/powerpc/kernel/legacy_serial.c
> drivers/tty/serial/8250/8250_fsl.c
> drivers/tty/serial/8250/8250_of.c
> include/linux/serial_8250.h
> 
> No users of fsl8250_handle_irq in 8250_port.c.

Ah right, I was too quick:

	8250_of.o uses fsl8250_handle_irq() from 8250_fsl.o
	8250_fsl.o uses serial8250_modem_status() from 8250_port.o (which is in 8250_base.o)


However linking 8250_fsl.o in 8250_of.o isn't a good solution either as
8250_fsl.o should also be available with CONFIG_SERIAL_OF_PLATFORM
disabled to provide the ACPI driver. And as 8250_of.o already depends on
8250_port.o (e.g. via serial8250_em485_config()) adding 8250_fsl.o
together with 8250_port.o into 8250_base.ko is fine and doesn't add new
dependencies.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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