Re: SYSFS "errors"

Em Mon, 18 Feb 2013 20:46:33 +0200
Felipe Balbi [off-list ref] escreveu:

Hi, On Mon, Feb 18, 2013 at 09:49:16AM -0800, Greg KH wrote:

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Input/output error - /sys/devices/cpu/power/autosuspend_delay_ms

The issue with this file is, if the power.use_autosuspend flag is not
set for the device, then it can't be read or written to.  This flag
changes dynamically with the system state
(__pm_runtime_use_autosuspend() can change it), so we can't just not
show the file if the flag is not set properly, sorry.

So the "error" is correct here, as is the 0644 file value.

hmm... we could create the file at pm_runtime_enable() time and remove
it on pm_runtime_disable() time, no ? Addin Rafael to Cc

...

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No such device - /sys/devices/system/edac/mc/mc0/sdram_scrub_rate

Odd, go ask the edac developers

will do ;-)

Well, the question is missing ;) /me assumes that you want to talk about
suspending/resume and EDAC, right?

In general, memory controllers don't supports suspend, as far as I can tell. 
Still, I've seen a few ones that support, but the current drivers and/or the
EDAC core currently doesn't offer any support to it, as such setup is done
by the BIOS, when it detects the used DIMM banks.

I suspect that, when the OS puts the machine on a suspend state, the BIOS may
also suspend also the memory controller or put it into a low power consumption
mode, but it does it without any help from the EDAC drivers.

For most of what's there at EDAC, I don't think it is worth to add any PM support
inside it. There are, however, two cases were we may need to add some support:

1) if user changed the SDRAM scrub rate before suspending, it makes sense to
restore it after resume, on the memory controller drivers that support such
feature (not all supports it);

2) hot-pluggable DIMMs. EDAC currently doesn't support. This could be needed
on some future. In this case, the core may need to re-scan the memory controller,
changing the memory properties. I've no idea if is there any real case needing
it, nor what event would trigger the memory-controller re-scan. Resume is likely
one of the candidates for it, on machines that support hot-pluggable memories.

Regards,
Mauro