linux-kernel - Re: [PATCH v2 23/25] tty: serial: samsung_tty: Add earlycon support for Apple UARTs

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Date:   Mon, 15 Feb 2021 20:17:48 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Hector Martin <marcan@...can.st>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Marc Zyngier <maz@...nel.org>, Rob Herring <robh@...nel.org>,
        Arnd Bergmann <arnd@...nel.org>,
        Olof Johansson <olof@...om.net>,
        Mark Kettenis <mark.kettenis@...all.nl>,
        Tony Lindgren <tony@...mide.com>,
        Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Stan Skowronek <stan@...ellium.com>,
        Alexander Graf <graf@...zon.com>,
        Will Deacon <will@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v2 23/25] tty: serial: samsung_tty: Add earlycon support
 for Apple UARTs

On Mon, Feb 15, 2021 at 09:17:11PM +0900, Hector Martin wrote:
> Earlycon support is identical to S3C2410, but Apple SoCs also need
> MMIO mapped as nGnRnE. This is handled generically for normal drivers
> including the normal UART path here, but earlycon uses fixmap and
> runs before that scaffolding is ready.
> 
> Since this is the only case where we need this fix, it makes more
> sense to do it here in the UART driver instead of introducing a
> whole fdt nonposted-mmio resolver just for earlycon/fixmap.
> 
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Hector Martin <marcan@...can.st>
> ---
>  drivers/tty/serial/samsung_tty.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/tty/serial/samsung_tty.c b/drivers/tty/serial/samsung_tty.c
> index e7ab0b9d89a7..00262f0e704b 100644
> --- a/drivers/tty/serial/samsung_tty.c
> +++ b/drivers/tty/serial/samsung_tty.c
> @@ -2988,6 +2988,23 @@ OF_EARLYCON_DECLARE(s5pv210, "samsung,s5pv210-uart",
>  			s5pv210_early_console_setup);
>  OF_EARLYCON_DECLARE(exynos4210, "samsung,exynos4210-uart",
>  			s5pv210_early_console_setup);
> +
> +/* Apple S5L */
> +static int __init apple_s5l_early_console_setup(struct earlycon_device *device,
> +						const char *opt)
> +{
> +	/* Close enough to S3C2410 for earlycon... */
> +	device->port.private_data = &s3c2410_early_console_data;
> +
> +#ifdef CONFIG_ARM64

if IS_ENABLED()
(unless it cannot be used due to missing symbol?)

> +	/* ... but we need to override the existing fixmap entry as nGnRnE */
> +	__set_fixmap(FIX_EARLYCON_MEM_BASE, device->port.mapbase,
> +		     __pgprot(PROT_DEVICE_nGnRnE));
> +#endif
> +	return samsung_early_console_setup(device, opt);

Don't you need to handle the error code - set PROT_DEFAULT() or whatever
was there before?

Best regards,
Krzysztof