Re: [linux-pm] [PATCH 3/6] [-mm]: ACPI: duplicate ACPI sleep "alarm" attribute in sysfs

Matthew Garrett
2007-01-08T10:10:26Z

On Sun, Jan 07, 2007 at 06:31:17PM -0800, David Brownell wrote:
> On Saturday 06 January 2007 9:57 pm, Matthew Garrett wrote:
> > Especially since /proc/acpi/alarm is just banging on the RTC registers
> > - the only ACPI thing about it is that the FADT can expose whether or
> > not the extended registers exist, and then making sure that the GPE is
> > enabled.
>
> The FADT also exposes whether the RTC can wake from S4. You may have
> noticed that my rtc-cmos patch #3 exported the relevant FADT info
> to the RTC device using platform_data, but the S4 wake capability flag
> isn't useful for anything on today's Linux.

Isn't useful in what way? It'd be helpful for userspace to know that now
that we're actually using S4 for swsusp, but I understand that it might
not fit into the current API terribly well.

> Not speaking as an ACPI expert, I do see the ACPI spec says (right
> under fig 4-11 in my version) that RTC events don't require GPEs.

Hmm. My interpretation of that section had been that RTC_EN and RTC_STS
were optional, and that a GPE would be required if they weren't
implemented. On re-reading it, I think you're right.

--
Matthew Garrett | mjg59@srcf.ucam.org