linux-kernel - Re: [PATCH] x86: mce: Honour bios-set CMCI threshold

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Message-ID: <20120827091235.GB26602@aftab.osrc.amd.com>
Date:	Mon, 27 Aug 2012 11:12:35 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:	tony.luck@...el.com, andi@...stfloor.org,
	gong.chen@...ux.intel.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
	linux-edac@...r.kernel.org, ananth@...ibm.com,
	Chris McDermott <lcm@...ibm.com>, masbock@...ux.vnet.ibm.com
Subject: Re: [PATCH] x86: mce: Honour bios-set CMCI threshold

On Thu, Aug 23, 2012 at 05:26:09PM +0530, Naveen N. Rao wrote:
> Sure - sounds like a good idea. Further, a #define could eliminate
> the need to change other references, but I'm not sure that's
> GENERALLacceptable
>
> #define mce_bios_cmci_threshold boot_flags.mce_bios_cmci_threshold
>
> could eliminate the need to change other references, but I'm not sure
> that's acceptable

Yeah, that's kinda obfuscating it for no reason. As I said before, we
can always add it later if it makes sense.

> But, I just had a quick look and it seems to me that these were
> defined as integers since they are exposed via sysfs. For instance:
> 
> static struct dev_ext_attribute dev_attr_cmci_disabled = {
>         __ATTR(cmci_disabled, 0644, device_show_int, set_cmci_disabled),
>         &mce_cmci_disabled
> };
> 
> Converting mce_cmci_disabled to a bit-field doesn't work since we
> take its address above. We could ignore and not set the second field
> at all (dev_ext_attribute->var) and define our own callbacks, but
> that'll be more work and I'm not sure if we work fine without

Right,

but take a look at set_cmci_disabled(): it converts the newly read value
to bool anyway:

        if (mce_cmci_disabled ^ !!new) {

so we can do later

	flags.mce_cmci_disabled = true;

or
	flags.mce_cmci_disabled = false;

instead of assigning 0 or 1 to it.

And, about showing it with device_show_int, a simple test works:

---
#include <stdio.h>
#include <stdbool.h>

int main()
{
        bool a = true;
        printf("%d\n", a);
        return 0;
}
--

but even if there are troubles with that, we can change device_show_int
to a locally defined function.

But, anyway, long story short: I wasn't suggesting you go and change all
of them - simply start by adding your flag mce_bios_cmci_threshold to a
struct <something>_flags and I'll take care of the rest.

Unless you really want to do it, of course :-)

Oh, and the more important thing is, Tony would need to review your
Intel-specific changes so pls keep him CCed on your next iteration too.

Thanks.

-- 
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
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