Subject: [PATCH] ARM: omap_hwmod: Add a new state to handle hwmods left enabled at init

From: [email-masked] (Kevin Hilman)
Date: Thu, 17 Nov 2011 11:35:11 -0800

Rajendra Nayak <[email-masked]> writes:

> A hwmod with a 'HWMOD_INIT_NO_IDLE' flag set, is left in
> enabled state by the hwmod framework post the initial setup.
> Once a real user of the device (a driver) tries to enable it
> at a later point, the hmwod framework throws a WARN() about
> the device being already in enabled state.
>
> Fix this by introducing a new state '_HWMOD_STATE_ENABLED_AT_INIT'
> to identify such devices/hwmods, so nothing but just a state
> change to '_HWMOD_STATE_ENABLED' can be done when the device/hwmod
> is requested to be enabled (the first time) by its driver/user.
>
> A good example of a such a device is an UART used as debug console.
> The UART module needs to be kept enabled through the boot, until the
> UART driver takes control of it, for debug prints to appear on
> the console.

Nice.  This is indeed much cleaner than what we're doing in the UART
code.  However...

> Signed-off-by: Rajendra Nayak <[email-masked]>
> ---
>  arch/arm/mach-omap2/omap_hwmod.c             |   16 ++++++++++++++--
>  arch/arm/plat-omap/include/plat/omap_hwmod.h |    1 +
>  2 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/omap_hwmod.c b/arch/arm/mach-omap2/omap_hwmod.c
> index d7f4623..7d94cc3 100644
> --- a/arch/arm/mach-omap2/omap_hwmod.c
> +++ b/arch/arm/mach-omap2/omap_hwmod.c
> @@ -1441,6 +1441,17 @@ static int _enable(struct omap_hwmod *oh)
>  
>  	pr_debug("omap_hwmod: %s: enabling\n", oh->name);
>  
> +	/*
> +	 * hwmods' with HWMOD_INIT_NO_IDLE flag set, are left

(no the ' isn't necessary)

> +	 * in enabled state at init.
> +	 * Now that someone is really trying to enable them,
> +	 * just update the state.
> +	 */
> +	if (oh->_state == _HWMOD_STATE_ENABLED_AT_INIT) {
> +		oh->_state = _HWMOD_STATE_ENABLED;
> +		return 0;
> +	}

...this subtly changes the behavior, at least compared to how the UART
code handles this today.

One thing that this doesn't do that the current UART code does is ensure
that the IP is actually in a state that can properly idle after this is
done.

For example, if the bootloader is dumb (most are) and has configured the
UARTs in mode that prevents idle (e.g. no-idle mode), then these UARTs
will never allow the SoC to hit low power states.

So, what's really needed is not just a return here, but an _idle() and
then continue so we know that the HW is in a state that we know can
idle from here on out.

Kevin