Re: [PATCH v2 2/3] x86/acpi: take rsdp address for boot params if available

From: Ingo Molnar
Date: Fri Dec 08 2017 - 02:05:16 EST



* Juergen Gross <jgross@xxxxxxxx> wrote:

> In case the rsdp address in struct boot_params is specified don't try
> to find the table by searching, but take the address directly as set
> by the boot loader.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> drivers/acpi/osl.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
> index 3bb46cb24a99..3b25e2ad7d75 100644
> --- a/drivers/acpi/osl.c
> +++ b/drivers/acpi/osl.c
> @@ -45,6 +45,10 @@
> #include <linux/uaccess.h>
> #include <linux/io-64-nonatomic-lo-hi.h>
>
> +#ifdef CONFIG_X86
> +#include <asm/setup.h>
> +#endif
> +
> #include "internal.h"
>
> #define _COMPONENT ACPI_OS_SERVICES
> @@ -195,6 +199,10 @@ acpi_physical_address __init acpi_os_get_root_pointer(void)
> if (acpi_rsdp)
> return acpi_rsdp;
> #endif
> +#ifdef CONFIG_X86
> + if (boot_params.hdr.acpi_rsdp_addr)
> + return boot_params.hdr.acpi_rsdp_addr;
> +#endif

Argh, that's typical short sighted hackery, layering violations and general
eyesore combined into a single patch ...

Those #ifdefs are a disgrace, plus why should generic ACPI code include platform
details like boot_params.hdr/acpi_rsdp_addr? It's also not very extensible to
non-x86 - so someone will have to redo this work for ARM64 as well in the future
...

So how about doing it right:

1)

Add a __weak acpi_arch_get_root_pointer() __weak function to drivers/acpi/osl.c:


__weak acpi_physical_address acpi_arch_get_root_pointer(void)
{
return 0;
}

2)

use it in acpi_os_get_root_pointer():

...
pa = acpi_arch_get_root_pointer();
if (pa)
return pa;
...

3)

Override the default variant in x86's acpi.c via something like:

acpi_physical_address acpi_arch_get_root_pointer(void)
{
return boot_params.hdr.acpi_rsdp_addr;
}

4)

Add this to arch/x86/include/asm/acpi.h:

extern acpi_physical_address acpi_arch_get_root_pointer(void);

5)

Add #include <asm/acpi.h> to drivers/acpi/osl.c.


That looks much cleaner, has no layering violations and is infinitely more
extensible, right?

Thanks,

Ingo