linux-kernel - Re: [PATCH] sparc: Use generic idle loop

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Date:	Mon, 08 Apr 2013 15:24:49 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sam@...nborg.org
Cc:	srivatsa.bhat@...ux.vnet.ibm.com, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	rusty@...tcorp.com.au, paulmck@...ux.vnet.ibm.com, mingo@...e.hu,
	peterz@...radead.org, magnus.damm@...il.com
Subject: Re: [PATCH] sparc: Use generic idle loop

From: Sam Ravnborg <sam@...nborg.org>
Date: Mon, 8 Apr 2013 19:10:35 +0200

> I think not.
> local_irq_disable writes 0 to the PIL register,
> whereas the above code set the IE (Interrupt enable) bit to 0.
> 
> So the implementations differs - and I think there is a good
> reason for being so.
> 
> But this is the part where I refer to that I am fooling around
> in code that I do not understand.
> I re-checked the SPARC V9 manual - but I did not within a few minutes
> reading understand what is the difference between the twoo.

Device interrupts arrive first as high-priority interrupt packets
that are serviced by traps which are enabled only if PSTATE.IE is
set.

These trap handlers reschedule the interrupt quickly into a PIL
levelled interrupt, whose delivery is covered by (%pil & PSTATE.IE)

The sun4v sleeping code requires that we have PSTATE.IE clear over
the cpu sleep hypervisor call.

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