linux-kernel - Re: [PATCH v10 0/8] Cavium MMC driver

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Message-ID: <20170120103758.GC3908@hardcore>
Date:   Fri, 20 Jan 2017 11:37:58 +0100
From:   Jan Glauber <jan.glauber@...iumnetworks.com>
To:     David Daney <ddaney@...iumnetworks.com>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Steven J . Hill" <Steven.Hill@...ium.com>
Subject: Re: [PATCH v10 0/8] Cavium MMC driver

On Thu, Jan 19, 2017 at 09:47:33AM -0800, David Daney wrote:
> On 01/19/2017 06:50 AM, Jan Glauber wrote:
> [...]
> >
> >>4) GPIO powers should be modelled as GPIO regulators. I believe we
> >>have discussed this earlier as well (I don't really recall in detail
> >>about the last things). It gives us the opportunity to via the
> >>regulator framework to find out the supported voltage levels. This is
> >>the generic method which is used by mmc drivers, you need to adopt to
> >>this as well.
> >
> >I've added a fixed regulator to DT:
> >
> >        vcc_3v3: regulator-vcc_3v3 {
> >                compatible = "regulator-fixed";
> >                regulator-name = "VCC_3V3";
> 
> 
> Very minor point not really directly related to the MMC driver:
> "VCC_3V3" implies a general purpose supply for many things on the
> board.  This is not the case for these boards.  The "regulator"
> controls power only to eMMC and SD devices, so a name that conveys
> that function should be invented.

OK, I'll rename it to:

	mmc_supply_3v3: mmc_supply_3v3 {
        	compatible = "regulator-fixed";
		regulator-name = "mmc_supply_3v3";
		[...]


> Actually on some boards GPIO 8 doesn't even control a regulator, but
> instead only activates a bus isolator on the control and data
> signals to the eMMC and SD devices.  In this case we would be using
> the regulator framework only because the code is already there and
> it happens to work, not because we actually have a regulator.
> 
> >                regulator-min-microvolt = <3300000>;
> >                regulator-max-microvolt = <3300000>;
> >
> >                gpio = <&gpio_6_0 8 0>;
> >                /* enable-gpio = <&gpio_6_0 8 0>; */
> >                enable-active-high;
> >        };
> >
> >This seems to enable the gpio. Is this sufficient or do I need the
> >gpio-regulator?
> >
> 
> Does the "regulator-fixed" allow us to properly turn it on and off?

Yes, I've disabled all gpio calls from our mmc driver, with only the gpio 
settings in the regulator entry I get:

root@sff:~# cat /sys/kernel/debug/gpio 
gpiochip0: GPIOs 464-511, parent: pci/0000:00:06.0, gpio_thunderx:
 gpio-472 (                    |mmc_supply_3v3      ) out hi 

So the regulator driver enables GPIO 8 as it should.

> If not, we may have to switch to "gpio-regulator".  Which ever is
> simplest should be used.

"regulator-fixed" seems sufficient to me as we don't need the additional
power states that "gpio-regulator" supports.

> [...]