linux-kernel - Re: [PATCH] ARM: OMAP5: Switch to THUMB mode if needed on secondary CPU

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Message-ID: <20140428164348.GA14354@e103592.cambridge.arm.com>
Date:	Mon, 28 Apr 2014 17:43:54 +0100
From:	Dave Martin <Dave.Martin@....com>
To:	Joel Fernandes <joelf@...com>
Cc:	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Nishanth Menon <nm@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH] ARM: OMAP5: Switch to THUMB mode if needed on secondary
 CPU

On Tue, Apr 22, 2014 at 01:31:46PM -0500, Joel Fernandes wrote:
> On my DRA7 system, when the kernel is built in THUMB mode, the secondary CPU
> (Cortex A15) fails to come up causing SMP boot on second CPU to timeout. This
> seems to be because the CPU is in ARM mode once the ROM hands over control to
> the kernel.  Switch to THUMB mode if required once the kernel is control of
> secondary CPU. On OMAP4 on the other hand, it appears to be in THUMB mode on
> entry so this is not required and SMP boot works as is.
> 
> Cc: Santosh Shilimkar <santosh.shilimkar@...com>
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Nishanth Menon <nm@...com>
> Cc: Tony Lindgren <tony@...mide.com>
> Signed-off-by: Joel Fernandes <joelf@...com>
> ---
>  arch/arm/mach-omap2/omap-headsmp.S |    8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mach-omap2/omap-headsmp.S b/arch/arm/mach-omap2/omap-headsmp.S
> index 75e9295..1809dce 100644
> --- a/arch/arm/mach-omap2/omap-headsmp.S
> +++ b/arch/arm/mach-omap2/omap-headsmp.S
> @@ -1,7 +1,7 @@
>  /*
>   * Secondary CPU startup routine source file.
>   *
> - * Copyright (C) 2009 Texas Instruments, Inc.
> + * Copyright (C) 2014 Texas Instruments, Inc.
>   *
>   * Author:
>   *      Santosh Shilimkar <santosh.shilimkar@...com>
> @@ -28,9 +28,13 @@
>   * code.  This routine also provides a holding flag into which
>   * secondary core is held until we're ready for it to initialise.
>   * The primary core will update this flag using a hardware
> -+ * register AuxCoreBoot0.
> + * register AuxCoreBoot0.
>   */
>  ENTRY(omap5_secondary_startup)

Are you sure this problem is not caused by the missing ENDPROC() for
omap5_secondary_startup?

You have END() instead (which may have been accidental).

Without ENDPROC(), the symbol is not marked as a function and so
the Thumb bit won't be set when taking a pointer -- so the kernel
is actually telling the firmware to enter in ARM state.

Try changing END() to ENDPROC() without this patch, and see if it
makes a difference.

If it still doesn't work, then the firmware either doesn't support
entering in ARM, or is buggy.

Cheers
---Dave

> +.arm
> +THUMB( adr     r9, BSYM(wait)  )       @ CPU may be entered in ARM mode.
> +THUMB( bx      r9              )       @ If this is a Thumb-2 kernel,
> +THUMB( .thumb                  )       @ switch to Thumb now.
>  wait:	ldr	r2, =AUX_CORE_BOOT0_PA	@ read from AuxCoreBoot0
>  	ldr	r0, [r2]
>  	mov	r0, r0, lsr #5
> -- 
> 1.7.9.5
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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