linux-kernel - Re: [RFC] regulator: add driver for MAX8660/8661

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Date:	Wed, 23 Sep 2009 16:38:15 +0200
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Liam Girdwood <lrg@...mlogic.co.uk>
Cc:	linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [RFC] regulator: add driver for MAX8660/8661

Hi Liam,

> Fwiw, the WM8350 has several similar boot up modes. Luckily we can read
> back this device to determine mode and any boot loader config. It may
> also be required to add any shadow register changes to your
> platform_data. i.e. if boot loader does any writes.

While I thought about how to achieve that (Specify voltages and convert them
back to selector-values? Ask for the selector value? Enforce a complete
register set?), I concluded that there are lots of details in here, and I'd
spare that for the case when it is actually needed. In our case, it is not.

> Btw, have you tried register read back ? The data sheet mentions a
> "bidirectional" I2C SDA line implying the device registers can be read
> back, even though they are all marked W in the register map.

The line itself has the capability of being bidirectional, still the chips has
no logic for being read. Page 37 states:

"The MAX8660/MAX8661 are write-only devices and recognize the 'write byte'
protocol as defined in the SMBus specification and shown in section A of Figure
11..."

And to be very sure, I just tried a read -> '-EIO'


> 
> > +The Target Voltage 2 Registers for V3, V4 and V5 are not used by this driver.
> > +
> > +Note that disabling V3 or V4 has no effect if pin EN34 is driven high (pin and
> > +register are ORed, see datasheet).
> > +
> 
> Sounds like EN34 status should be in platform_data.

Good idea, will implement that.

Regards,

   Wolfram

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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