[U-Boot] OMAP3 performance regression in 2011.12

[Joe Woodward <jw@terrafix.co.uk>]

> -----Original Message-----
> From: Tom Rini <tom.rini@gmail.com>
> To: Joe Woodward <jw@terrafix.co.uk>
> Cc: u-boot at lists.denx.de
> Date: Mon, 9 Jan 2012 08:11:07 -0700
> Subject: Re: [U-Boot] OMAP3 performance regression in 2011.12
> 
> > On Mon, Jan 9, 2012 at 3:27 AM, Joe Woodward <jw@terrafix.co.uk>
> wrote:
> > > Commit "armv7: disable L2 cache in cleanup_before_linux()" on 6th
> Dec
> > 2011 by Aneesh V adds the following:
> > >
> > > arch/arm/cpu/armv7/cpu.c:cleanup_before_linux()
> > >
> > > ...
> > > v7_out_cache_disable();
> > > ...
> > >
> > > The commit message implies this change was to make booting reliable
> > on OMAP4 by disabling L2 cache before jumping to Linux.
> > >
> > > However, when running with a stock 3.2 Linux kernel on an OMAP3 it
> > has the effect of massively reducing system performance (when running
> > using an OMAP3-
> > > only 3.2 Linux Kernel on a GUSMTIX Overo OMAP3530).
> > >
> > > Therefore, I assume this means that the kernel isn't turning the L2
> > cache back on for an OMAP3 (at least with my kernel build)!
> > >
> > > So, my question is...
> > >
> > > Are there any Kconfig options in Linux that will re-enable the L2
> > cache (something obvious that I've missed), or is this commit just
> > bad-news for OMAP3?
> > 
> > Are you certain that this is the commit that's causing your problem?
> > The kernel is responsible for turning the cache back on and has for a
> > long time, iirc.
> > 
> > -- 
> > Tom

(apologies for previous top posting, wasn't paying attention to what I was doing!)

I'm fairly certain...

If I take the 2011.12 uBoot release the kernel takes about twice the time to boot (compared to 2011.09), and the device is noticably slower.

Then if I comment out the v7_out_cache_disable() line in cpu.c and rebuild uBoot then everything speeds up again.
 
I thought the kernel would turn on the cache again too...

Is there any easy way from userspace to determine if the cache is on?

I did a bit of Googling and found:
http://www.spinics.net/lists/arm-kernel/msg50064.html
http://www.spinics.net/lists/arm-kernel/msg50083.html

It may be that the kernel is re-enabling the L1 cache, but expecting L2 to be on?
Or the way v7_out_cache_disable() disables L2 is not compatible with the way the kernel expects to re-enable it?

Also, in the Linux there seem to be OMAP4 specific functions for re-enabling the L2 cache (omap4-common.c:omap_l2_cache_init()), but none for OMAP3. I'm 
assuming this is because up to now OMAP3 is assumed to have the L2 left enabled? Either that, or there is some generic Cortex-A8 method for enabling the L2 
cache in the kernel soures that I've not found...

Cheers,
Joe

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