Re: [PATCH] save and restore etm state across core OFF modes

[Tony Lindgren <tony@atomide.com>]

* Nishanth Menon <nm@ti.com> [100112 14:06]:
> Alexander Shishkin had written, on 01/12/2010 03:46 PM, the following:
> >On Tue, Jan 12, 2010 at 01:04:04 -0800, Tony Lindgren wrote:
> >>* Nishanth Menon <nm@ti.com> [100112 09:31]:
> >>>Alexander Shishkin had written, on 01/12/2010 11:30 AM, the following:
> >>>>On Tue, Jan 12, 2010 at 11:13:13 -0600, Nishanth Menon wrote:
> >>>>>Alexander Shishkin had written, on 01/12/2010 11:04 AM, the following:
> >>>>>>diff --git a/arch/arm/mach-omap2/sleep34xx.S b/arch/arm/mach-omap2/sleep34xx.S
> >>>>>>index 69521be..0a5ec86 100644
> >>>>>>--- a/arch/arm/mach-omap2/sleep34xx.S
> >>>>>>+++ b/arch/arm/mach-omap2/sleep34xx.S
> >>>[...]
> >>>>>>	/* Store current cpsr*/
> >>>>>>	mrs	r2, cpsr
> >>>>>>	stmia	r8!, {r2}
> >>>>>>@@ -520,6 +616,7 @@ clean_caches:
> >>>>>>	cmp	r9, #1 /* Check whether L2 inval is required or not*/
> >>>>>>	bne	skip_l2_inval
> >>>>>>clean_l2:
> >>>>>>+#if 0
> >>>>>my aversion to #if 0 kicks in here :(.. do we have an alternative
> >>>>>like using the CONFIG_ENABLE_OFF_MODE_JTAG_ETM_DEBUG or something
> >>>>>else?
> >>>>Fair enough. I could replace it with "#if !defined(...)" as the first
> >>>>thing that comes to mind. This way it will only take disabling the
> >>>>config option to catch any possible regressions in between. Does this
> >>>>sound reasonable?
> >>>sounds ok to me.. unless folks have ideas coz of clean_l2 label..
> >>>more comments might be useful before a rev2 of the patch..
> >>The best solution would be to be able to toggle this via sysfs or
> >>debugfs by swapping the sram code for idle loop when JTAG support
> >>is needed.
> >
> >Well, if you say, compile the ETM driver in, this will be needed most of
> >the time.
> >
> I can think of reasons for an against a sysfs entry (as part of
> discussion -warning lot of self contradictions below- but I think
> might save a bit of back and froth ;)):
> 
> for sysfs entry:
> a) save and restore will have additional latency when you save a
> chunk such as EMU domain regs - this will not be needed in
> production phones, disabling it might pop up surprises

There's no overhead if you're just replacing the function
loaded to SRAM as needed. But for sure it's a debug tool only.

Regards,

Tony