Re: [RFC PATCH 04/10] mfd: Add base driver for Netronix embedded controller

["Jonathan Neuschäfer" <j.neuschaefer@gmx.net>]

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On Sat, Jun 27, 2020 at 10:17:38AM +0200, Andreas Kemnade wrote:
> On Sun, 21 Jun 2020 00:42:15 +0200
> Jonathan Neuschäfer <j.neuschaefer@gmx.net> wrote:
> 
> > Third-party hardware documentation is available at
> > https://github.com/neuschaefer/linux/wiki/Netronix-MSP430-embedded-controller
> > 
> > The EC supports interrupts, but the driver doesn't make use of them so
> > far.
> > 
> > Known problems:
> > - The reboot handler is installed in such a way that it directly calls
> >   into the i2c subsystem to send the reboot command to the EC. This
> >   means that the reboot handler may sleep, which is not allowed.
> > 
> see
> https://patchwork.ozlabs.org/project/linux-i2c/patch/20190415213432.8972-3-contact@stefanchrist.eu/
> 
> for a fix of such problems. 

So far, regmap isn't involved here, but I'll remember it when I switch
to regmap.

Between when I first wrote this driver and now, the I2C has added
support for transfers in atomic contexts very late in the system's life
(exactly what happens when you reset a system via PMIC/EC), so this
problem seems to be gone from my driver, for now.
(See commit 63b96983a5ddf ("i2c: core: introduce callbacks for atomic transfers"))


[...]
> > +int ntxec_write8(struct ntxec *ec, u8 addr, u8 value)
> > +{
> > +	return ntxec_write16(ec, addr, value << 8);
> > +}
> > +EXPORT_SYMBOL(ntxec_write8);
> > +
> 
> do we really need both 16bit and 8bit accessors?

No, the hardware/firmware doesn't care.

> If not, then simply use regmap_i2c_init and set val_bits accordingly.
> Maybe just doing the << 8 in the constants?

Thanks, I'll try this approach.

The values are not always constants, for example in the PWM driver:

	res |= ntxec_write8(pwm->ec, NTXEC_PERIOD_HIGH, period >> 8);
	res |= ntxec_write8(pwm->ec, NTXEC_PERIOD_LOW, period);
	res |= ntxec_write8(pwm->ec, NTXEC_DUTY_HIGH, duty >> 8);
	res |= ntxec_write8(pwm->ec, NTXEC_DUTY_LOW, duty);


Jonathan

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