[PATCH] arm: Allow mounting root on omaps with CPU_V6 and CPU_V7

[PATCH] arm: Allow mounting root on omaps with CPU_V6 and CPU_V7

[Tony Lindgren]

Hi all,

Here's one more patch for booting CPU_V6 and CPU_V7 omaps
with the same kernel binary. This is needed to boot to
user space, earlier I was just checking for "Mounted root".

Now I'm wondering if some of these should be done as

default y if CPU_V7 && !CPU_32v6K

or 

default y if CPU_V7 && !CPU_V6

instead to make them more generic? This is, after the
earlier patch selecting CPU_32v6K if !ARCH_OMAP2.

Regards,

Tony


From: Tony Lindgren <tony@atomide.com>
Date: Thu, 18 Feb 2010 13:22:58 -0800
Subject: [PATCH] arm: Allow mounting root on omaps with CPU_V6 and CPU_V7

To mount root, we need to disable VFPv3, HAS_TLS_REG, and
set ARM_L1_CACHE_SHIFT=5.

Otherwise we'll get something like this for CPUv3:

Freeing init memory: 184K
Internal error: Oops - undefined instruction: 0 [#1]
last sysfs file:
Modules linked in:
CPU: 0    Not tainted  (2.6.33-rc8-07824-gf2e1d91-dirty #36)
PC is at no_old_VFP_process+0x8/0x3c
LR is at __und_usr_unknown+0x0/0x14
...

Or the system just hangs if HAS_TLS_REG is set.

The ARM_L1_CACHE_SHIFT most likely will cause issues
too if not set to 5.

Signed-off-by: Tony Lindgren <tony@atomide.com>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 554cb9c..89dba0b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1498,7 +1498,7 @@ config VFP
 config VFPv3
 	bool
 	depends on VFP
-	default y if CPU_V7
+	default y if CPU_V7 && !ARCH_OMAP2
 
 config NEON
 	bool "Advanced SIMD (NEON) Extension support"
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 4c2e90d..800f0ce 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -718,7 +718,7 @@ config TLS_REG_EMUL
 config HAS_TLS_REG
 	bool
 	depends on !TLS_REG_EMUL
-	default y if SMP || CPU_32v7
+	default y if (SMP || CPU_32v7) && !ARCH_OMAP2
 	help
 	  This selects support for the CP15 thread register.
 	  It is defined to be available on some ARMv6 processors (including
@@ -779,5 +779,5 @@ config CACHE_XSC3L2
 
 config ARM_L1_CACHE_SHIFT
 	int
-	default 6 if ARCH_OMAP3 || ARCH_S5PC1XX
+	default 6 if (ARCH_OMAP3 || ARCH_S5PC1XX) && !ARCH_OMAP2
 	default 5

[PATCH] arm: Allow mounting root on omaps with CPU_V6 and CPU_V7

[Russell King - ARM Linux]

On Thu, Feb 18, 2010 at 04:27:48PM -0800, Tony Lindgren wrote:
> @@ -779,5 +779,5 @@ config CACHE_XSC3L2
>  
>  config ARM_L1_CACHE_SHIFT
>  	int
> -	default 6 if ARCH_OMAP3 || ARCH_S5PC1XX
> +	default 6 if (ARCH_OMAP3 || ARCH_S5PC1XX) && !ARCH_OMAP2
>  	default 5

This one is definitely wrong.  Setting the L1 cache line size larger
than it actually is should be safe; setting it smaller is definitely
unsafe.

[PATCH] arm: Allow mounting root on omaps with CPU_V6 and CPU_V7

[Tony Lindgren]

* Russell King - ARM Linux <linux@arm.linux.org.uk> [100219 00:33]:
> On Thu, Feb 18, 2010 at 04:27:48PM -0800, Tony Lindgren wrote:
> > @@ -779,5 +779,5 @@ config CACHE_XSC3L2
> >  
> >  config ARM_L1_CACHE_SHIFT
> >  	int
> > -	default 6 if ARCH_OMAP3 || ARCH_S5PC1XX
> > +	default 6 if (ARCH_OMAP3 || ARCH_S5PC1XX) && !ARCH_OMAP2
> >  	default 5
> 
> This one is definitely wrong.  Setting the L1 cache line size larger
> than it actually is should be safe; setting it smaller is definitely
> unsafe.

OK dropped that part, updated patch below. Maybe the VFPv3
code can be fixed to boot on earlier hardware too.

So I guess ARM_L1_CACHE_SHIFT should be only used for alignment, and
not for for cache operations?

If so, then what have in arch/arm/plat-omap/iommu.c seems buggy:

static void flush_iopgd_range(u32 *first, u32 *last)
{
	/* FIXME: L2 cache should be taken care of if it exists */
	do {
		asm("mcr	p15, 0, %0, c7, c10, 1 @ flush_pgd"
		    : : "r" (first));
		first += L1_CACHE_BYTES / sizeof(*first);
	} while (first <= last);
}

It seems that this code should use the real cache line size instead to
avoid every other line not to flush if ARM_L1_CACHE_SHIFT is set larger
than it is.

Regards,

Tony
-------------- next part --------------
A non-text attachment was scrubbed...
Name: v6-v7-mount-root-v2.patch
Type: text/x-diff
Size: 1374 bytes
Desc: not available
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20100219/fb979dbd/attachment.bin>

[PATCH] arm: Allow mounting root on omaps with CPU_V6 and CPU_V7

[Russell King - ARM Linux]

On Fri, Feb 19, 2010 at 10:03:32AM -0800, Tony Lindgren wrote:
> If so, then what have in arch/arm/plat-omap/iommu.c seems buggy:
> 
> static void flush_iopgd_range(u32 *first, u32 *last)
> {
> 	/* FIXME: L2 cache should be taken care of if it exists */
> 	do {
> 		asm("mcr	p15, 0, %0, c7, c10, 1 @ flush_pgd"
> 		    : : "r" (first));
> 		first += L1_CACHE_BYTES / sizeof(*first);
> 	} while (first <= last);
> }
> 
> It seems that this code should use the real cache line size instead to
> avoid every other line not to flush if ARM_L1_CACHE_SHIFT is set larger
> than it is.

Yes.