linux-kernel - RE: [RFC PATCH 0/3] mca

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Date:	Wed, 10 Oct 2012 15:35:56 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Borislav Petkov <bp@...64.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <borislav.petkov@....com>,
	"jejb@...isc-linux.org" <jejb@...isc-linux.org>,
	"deller@....de" <deller@....de>
Subject: RE: [RFC PATCH 0/3] mca_config stuff

> Therefore, I can toggle the bits in the mce code with mca_cfg.<bitname>.
> When defining accessing them through the device attributes in sysfs, I
> use a new macro DEVICE_BIT_ATTR which gets the corresponding bit number
> of that same bit in the bitfield. This gives only one function which
> operates on a bitfield instead of a single function per bit in the
> bitfield.

Is this true across all architectures? I know that pa-risc instructions
that operate on bitfields use "0" to operate on the high order bit
rather than the low order one. I don't recall whether this spills over
into the compiler. If it did, then you'd have to have different #defines
for the bit numbers[1].  For this specific use case it wouldn't matter because
you are just using it in x86 code. But device_store_bit() and device_show_bit()
are in generic code - so they must be able to work across all architectures.

-Tony

[1] Or fix the store/show bit functions to transform the bit numbers from
"little-bitian" to "big-bitian" on architectures that count the other way.
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