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

[Arnd Bergmann <arnd@kernel.org>]

On Mon, Feb 15, 2021 at 8:19 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
> On Mon, Feb 15, 2021 at 09:17:11PM +0900, Hector Martin wrote:

> > +
> > +/* 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

It has to be a preprocessor conditional because PROT_DEVICE_nGnRnE
is only defined on arm64. We could add a FIXMAP_PAGE_NONPOSTED
alias for it that defaults to FIXMAP_PAGE_IO, but in the end this is
really an architecture specific thing and I think leaving it guarded by
the architecture is appropriate.

> > +     return samsung_early_console_setup(device, opt);
>
> Don't you need to handle the error code - set PROT_DEFAULT() or whatever
> was there before?

__set_fixmap() has no return value, it just writes a page table entry and
does not fail.

      Arnd