About HPET is_hpet_capable()

[Stratos Psomadakis]

On 08/09/2011 11:28 AM, limp wrote:
> Hi all,
>
> I am having a deeper look on Linux hpet code and I was wondering how exactly
> is_hpet_capable() works.
> >From the name of it, I assume that this function checks if the system
> supports HPET or not but I can't really tell how it does that.
>
> The function is the following:
>
> static inline int is_hpet_capable(void)
> {
>          return !boot_hpet_disable && hpet_address;
> }
>
> Could anyone help me understand how this works?
>
> Regards.
>
>
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boot_hpet_disable is a boot time param, which as the name suggests
disables the hpet timer(nohpet is the actual parameter given to the
kernel by the bootloader I think)...

hpet_address is the address where the hpet timers are mapped, which is
read by the kernel from the BIOS ACPI table for hpet I think...

If you look at the code that does the actual initialization for hpet,
it's a bit more complicated than that, but generally, this function
checks whether HPET is disabled at boot time, and if a suitable entry /
address for HPET timers is found in the BIOS ACPI tables (if it's not
found, the hpet_address will be NULL). So if hpet is enabled, and an
address is found, this function returns 1/true. Else 0/false.

-- 
Stratos Psomadakis
<s.psomadakis at gmail.com>