linux-kernel - RE: [PATCH 5/5] regulator: Support AP watchdog reset operation for s5m8767a

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Date:	Thu, 14 Jun 2012 09:01:39 +0900
From:	Sangbeom Kim <sbkim73@...sung.com>
To:	'Mark Brown' <broonie@...nsource.wolfsonmicro.com>
Cc:	'Liam Girdwood' <lrg@...com>, linux-kernel@...r.kernel.org,
	sameo@...ux.intel.com, sbkim01@...il.com
Subject: RE: [PATCH 5/5] regulator: Support AP watchdog reset operation for
 s5m8767a

Hi Mark,
I'm sorry for insufficient explanation.
Basically, PMIC can't know status of ap reset.
Problem can be happened like below.

- AP Bootable lowest arm voltage: 0.9v
- AP arm voltage table for DVFS: 0.8v, 0.9v, 1.0v
- During AP works on 0.8v, watchdog reset is asserted
- AP can't boot, because vdd arm is still 0.8v

Solution
- Basic concept: After ap watchdog reset, GPIO configuration is changed by default value
- S5M8767A has function of voltage control with gpio (8 levels with 3 gpios)
- Set bootable voltage on level 0 -> can work with default gpio configuration
- In the probing, Change voltage control level from level 0 to level 1
- Execute normal dvfs operation on level 1
- After watchdog reset, ap gpio is set by default value
- PMIC operation mode is changed by ap reset (level1 -> level0)
- AP can execute normal boot

If you have any question, email me again.
Thanks,
Sangbeom.

> -----Original Message-----
> From: Mark Brown [mailto:broonie@...nsource.wolfsonmicro.com]
> Sent: Thursday, June 14, 2012 2:46 AM
> To: Sangbeom Kim
> Cc: 'Liam Girdwood'; linux-kernel@...r.kernel.org; sameo@...ux.intel.com; sbkim01@...il.com
> Subject: Re: [PATCH 5/5] regulator: Support AP watchdog reset operation for s5m8767a
> 
> On Wed, Jun 13, 2012 at 05:28:47PM +0900, Sangbeom Kim wrote:
> > After AP watchdog reset, S5M8767A should be reset too.
> > If AP is set on lowest voltage, AP can't execute boot sequence.
> > This patch support watchdog reset of s5m8767.
> 
> It's really hard to see how this patch addresses the issue above - could you explain in more
> detail, please?

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