linux-kernel - Re: [PATCH v2 1/1] mfd: palmas: Add power off control

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Date:	Fri, 2 Aug 2013 09:39:27 -0500
From:	Nishanth Menon <nm@...com>
To:	Bill Huang <bilhuang@...dia.com>
CC:	"sameo@...ux.intel.com" <sameo@...ux.intel.com>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"pawel.moll@....com" <pawel.moll@....com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"ian.campbell@...rix.com" <ian.campbell@...rix.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"lee.jones@...aro.org" <lee.jones@...aro.org>,
	"broonie@...aro.org" <broonie@...aro.org>,
	"j-keerthy@...com" <j-keerthy@...com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"ian@...mlogic.co.uk" <ian@...mlogic.co.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mallikarjun Kasoju <mkasoju@...dia.com>
Subject: Re: [PATCH v2 1/1] mfd: palmas: Add power off control

On 08/02/2013 12:45 AM, Bill Huang wrote:
> On Thu, 2013-08-01 at 21:08 +0800, Nishanth Menon wrote:
>> On 04:08-20130801, Bill Huang wrote:
>>> On Wed, 2013-07-31 at 19:57 +0800, Nishanth Menon wrote:
>>>>
>>>> If you notice the reference code I send, atleast on TWL6035/37 variants
>>>> of Palmas, USB IRQ unmask is mandatory for power on with USB cable -
>>>> example usage scenario: extremely low battery, device powered off, plug
>>>> in usb cable to restart charging - you'd like to initiate charging logic
>>>> in bootloader, but that wont work if the device does not do OFF-ON
>>>> transition with usb cable plugged in for vbus.
>>>>
>>> Why do we need to add Palmas USB_IRQ unmask logic in shutdown? Does that
>>> mean for all platform using Palmas has to unmask USB IRQ (including
>>> those do not power vbus through Palmas)? Can't we just have a simple
>>> shutdown function but have the VBus programming been done in USB driver
>>> or maybe platform driver since it is platform specific control?
>> we dont have a irq cleanup, irq handling is done in palmas-mfd. Further,
>>
>> Why would USB driver care about vbus supply needs in complete power off
>> - it is the job of palmas driver? Further, palmas-mfd shutdown
>> handler(currently missing) if probably cleansup things:
>>
>>   mfd_remove_devices(palmas->dev);
>>    palmas_irq_exit(palmas);
>>
>> shutdown sequence becomes complicated further esp if things are
>> cleanedup in shutdown (Dummy patch[1]).
>>
>>
>> All I am saying is this: shutdown should allow powerup functionality to
>> work as well, how we do that is upto us - I personally found it a little
>> easier to keep the IRQ unmask in shutdown easier to deal with, but other
>> options might be possible as well.
>
> I'm not sure if I understand your comments completely (maybe due to I'm
> not familiar with the mechanism of unmasking USB IRQ in Palmas driver)

This is IMHO an weird configuration I saw on TWL6035/6037 Palmas device 
- so I suspect should be the case in probably other palmas devices as 
well. I hit power off, and I can start up the device again by supplying 
vbus -(usecase was, at that point in time, battery charging)

anyways, I was working with busybox and no usb driver even enabled, but 
I am told by the twl6035/7 support folks that due to design USB IRQ 
needs to be unmasked at shutdown/poweroff to allow OFF->ON transition 
sequence to start inside Palmas when vbus is supplied.


> but doing cleanup in each driver shutdown handler makes sense to me, if
> those clean up can be done in shutdown then we can make power off
> function as simple as possible and being part of Palmas mfd driver?

not really, mfd shutdown does not guarantee rest of the drivers' 
shutdown functions are safely called, pm_power_off unfortunately is the 
only "official point" where we can safely and cleanly shutdown the system.

-- 
Regards,
Nishanth Menon
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