linux-kernel - Re: [PATCH v3 3/7] mfd: Add MFD driver for ATC260x PMICs

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Message-ID: <20201221115713.GA155203@BV030612LT>
Date:   Mon, 21 Dec 2020 13:57:13 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...il.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Andreas Färber <afaerber@...e.de>,
        linux-actions@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 3/7] mfd: Add MFD driver for ATC260x PMICs

On Mon, Dec 21, 2020 at 08:10:15AM +0000, Lee Jones wrote:
> On Fri, 18 Dec 2020, Cristian Ciocaltea wrote:
> 
> > On Fri, Dec 18, 2020 at 01:21:39PM +0000, Lee Jones wrote:
> > > On Fri, 18 Dec 2020, Cristian Ciocaltea wrote:
> > > 
> > > > Hi Lee,
> > > > 
> > > > Thank you for the detailed review!
> > > > 
> > > > I will prepare a new revision, but there are still a couple of open
> > > > points..
> > > 
> > > Could you please snip your replies, leaving only the open points.
> > > 
> > > Scrolling through lots of empty quotes or "done" comments is quite
> > > time consuming.  Thanks.
> > 
> > Sure, I'll take that into account.
> > 
> > > [...]
> > > 
> > > > > > +	ret = regmap_read(atc260x->regmap, atc260x->rev_reg, &chip_rev);
> > > > > > +	if (ret) {
> > > > > > +		dev_err(dev, "Failed to get chip revision\n");
> > > > > > +		return ret;
> > > > > > +	}
> > > > > > +
> > > > > > +	if (chip_rev < 0 || chip_rev > 31) {
> > > > > > +		dev_err(dev, "Unknown chip revision: %d\n", ret);
> > > > > > +		return -EINVAL;
> > > > > > +	}
> > > > > 
> > > > > This still seems limiting.
> > > > 
> > > > This is based on the vendor implementation. Unfortunately I don't have
> > > > access to a data sheet or any other source of information about the
> > > > management of the chip revisions.
> > > 
> > > So which versions does this driver work with?  All 32?
> > 
> > I'm not even sure there are so many revisions, I guess that's just a
> > rough validation for a vendor reserved range.
> > 
> > For the moment, the only place where the functionality is affected
> > by the chip revision is in the regulator driver - there is a special
> > handling for the ATC2603C rev.B chip variant.
> > 
> > I expect some additional handling might be required for new drivers
> > bringing support for the other functions provided by the hardware.
> 
> The current patch seems to insinuate that 32 versions are currently
> supported.  What is the chip_rev for the ATC2603C rev.B?

I only own the rev.A for the ATC2603C variant, for which I read '0' from
the chip rev register.

However what really matters for the driver is not the raw value, but the
one computed via:

atc260x->ic_ver = __ffs(chip_rev + 1U);

This is basically a translation of the raw value to a chip version
that is used in the context of the special handling mentioned above:

enum atc260x_ver {
	ATC260X_A = 0,
	ATC260X_B,
	ATC260X_C,
	ATC260X_D,
	ATC260X_E,
	ATC260X_F,
	ATC260X_G,
	ATC260X_H,
};

So we actually could handle up to 8 chip versions with the current
management scheme.

> -- 
> Lee Jones [李琼斯]
> Senior Technical Lead - Developer Services
> Linaro.org │ Open source software for Arm SoCs
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