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

[Nishanth Menon]

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/