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

[Juergen Gross <jgross@xxxxxxxx>]

On 08/12/17 08:05, Ingo Molnar wrote:
> 
> * 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?

Right.

Thanks for the very constructive comment.


Juergen

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