Re: [PATCH 02/12] ARM: OMAP3: Store reboot mode in scratchpad on OMAP34xx - Russell King

From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Juha Yrjola <juha.yrjola@solidboot.com>
Cc: Tony Lindgren <tony@atomide.com>,
	linux-arm-kernel@lists.arm.linux.org.uk,
	Kevin Hilman <khilman@deeprootsystems.com>,
	linux-omap@vger.kernel.org
Subject: Re: [PATCH 02/12] ARM: OMAP3: Store reboot mode in scratchpad on OMAP34xx
Date: Mon, 16 Mar 2009 22:21:46 +0000	[thread overview]
Message-ID: <20090316222146.GA8150@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <49BE8F08.3000100@solidboot.com>

On Mon, Mar 16, 2009 at 07:40:24PM +0200, Juha Yrjola wrote:
> Russell King - ARM Linux wrote:
>
>> Right.  You are aware that there is already a mechanism for doing this
>> in the generic kernel (obviously not)?
>
> I am. Unfortunately, glibc fails to support this mechanism, as you say.  
> I didn't want to start making such intrusive changes for our trivial 
> need.

Yes, glibc sucks with that - they hide the Linux reboot syscall.
Luckily, it is accessible via the syscall() interface:

#include <linux/reboot.h>

int sys_reboot(const char *cmd)
{
	return syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2C,
			LINUX_REBOOT_CMD_RESTART2, cmd);
}

>> sys_reboot() with LINUX_REBOOT_CMD_RESTART2 takes a string in addition
>> to the standard parameters.  This string is passed into machine_restart()
>> which we currently ignore.  If LINUX_REBOOT_CMD_RESTART is used, this
>> string is NULL.
>>
>> We could change machine_restart() to pass this parameter through to
>> arm_pm_restart() and ultimately down to arch_reset().
>
> Sure. With RESTART2, I could've even used the reboot notifier chain with  
> an OMAP3-specific driver to store the string.

The notifier chain is called in any case.

> Are you suggesting to get rid of reboot_mode altogether? If not, could  
> we still have the sysfs mechanism? A one-character reboot_mode would be  
> plenty enough for us.

No, reboot mode tells _how_ to perform the reboot - whether that be
by hardware reset, gpio reset or a soft call via the reset address.
It's not supposed to tell the boot loader what to do.