linux-kernel - Re: [PATCH 01/11] mfd: add the Berlin controller driver

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Message-ID: <20150217092020.GC4507@kwain>
Date:	Tue, 17 Feb 2015 10:20:20 +0100
From:	Antoine Tenart <antoine.tenart@...e-electrons.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Antoine Tenart <antoine.tenart@...e-electrons.com>,
	sebastian.hesselbarth@...il.com, sameo@...ux.intel.com,
	jszhang@...vell.com, zmxu@...vell.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/11] mfd: add the Berlin controller driver

Lee,

On Mon, Feb 16, 2015 at 12:48:08PM +0000, Lee Jones wrote:
> On Wed, 11 Feb 2015, Antoine Tenart wrote:
> 
> > --- a/drivers/mfd/Kconfig
> > +++ b/drivers/mfd/Kconfig
> > @@ -840,6 +840,11 @@ config STMPE_SPI
> >  	  This is used to enable SPI interface of STMPE
> >  endmenu
> >  
> > +config MFD_BERLIN_CTRL
> > +	bool
> 
> Missing description.
> Why can't this driver be built as a module?

Well, this mfd driver registers various devices as the pinctrl and the
reset driver. I think we want the pinctrl driver to always be
registered.

IMHO we want this driver to always be selected when using a Berlin SoC.

> 
> > +	select MFD_CORE
> > +	select MFD_SYSCON
> 
> Missing help.
> 
> >  config MFD_STA2X11
> >  	bool "STMicroelectronics STA2X11"
> >  	depends on STA2X11
> > diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> > index 53467e211381..adf60e85df20 100644
> > --- a/drivers/mfd/Makefile
> > +++ b/drivers/mfd/Makefile
> > @@ -179,3 +179,5 @@ obj-$(CONFIG_MFD_DLN2)		+= dln2.o
> >  
> >  intel-soc-pmic-objs		:= intel_soc_pmic_core.o intel_soc_pmic_crc.o
> >  obj-$(CONFIG_INTEL_SOC_PMIC)	+= intel-soc-pmic.o
> > +
> > +obj-$(CONFIG_MFD_BERLIN_CTRL)	+= berlin-ctrl.o
> > diff --git a/drivers/mfd/berlin-ctrl.c b/drivers/mfd/berlin-ctrl.c
> > new file mode 100644
> > index 000000000000..e3ce6f069f16
> > --- /dev/null
> > +++ b/drivers/mfd/berlin-ctrl.c
> > @@ -0,0 +1,180 @@
> > +/*
> > + * Copyright (C) 2015 Marvell Technology Group Ltd.
> > + *
> > + * Antoine Tenart <antoine.tenart@...e-electrons.com>
> 
> Author: Antoine Tenart <antoine.tenart@...e-electrons.com>

Hmmm, okay.

> 
> > +
> > +#include <linux/mfd/core.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> 
> kernel.h?

Is there a reason to add this header here?

> > +/*
> > + * BG2 devices
> > + */
> > +static const struct mfd_cell berlin2_ctrl_chip_ctrl_subdevs[] = {
> > +	{
> > +		.name		= "berlin2-soc-pinctrl",
> > +		.of_compatible	= "marvell,berlin2-soc-pinctrl",
> > +	},
> > +	{
> > +		.name		= "berlin2-reset",
> > +		.of_compatible	= "marvell,berlin2-reset",
> > +	},
> > +};
> > +
> > +static const struct mfd_cell berlin2_ctrl_system_ctrl_subdevs[] = {
> > +	{
> > +		.name		= "berlin2-system-pinctrl",
> > +		.of_compatible	= "marvell,berlin2-system-pinctrl",
> > +	},
> > +};
> > +
> > +static const struct berlin_ctrl_priv berlin2_ctrl_chip_ctrl_data = {
> > +	.devs	= berlin2_ctrl_chip_ctrl_subdevs,
> > +	.ndevs	= ARRAY_SIZE(berlin2_ctrl_chip_ctrl_subdevs),
> > +};
> > +
> > +static const struct berlin_ctrl_priv berlin2_ctrl_system_data = {
> > +	.devs	= berlin2_ctrl_system_ctrl_subdevs,
> > +	.ndevs	= ARRAY_SIZE(berlin2_ctrl_system_ctrl_subdevs),
> > +};
> > +
> > +
> 
> Superfluous '\n'

Sure.

> 
> > +
> > +static int berlin_ctrl_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	const struct of_device_id *match;
> > +	const struct berlin_ctrl_priv *priv;
> > +	int ret;
> > +
> > +	match = of_match_node(berlin_ctrl_of_match, dev->of_node);
> > +	if (!match)
> > +		return -EINVAL;
> > +
> > +	priv = match->data;
> > +
> > +	ret = mfd_add_devices(dev, 0, priv->devs, priv->ndevs, NULL, -1, NULL);
> > +	if (ret) {
> > +		dev_err(dev, "Failed to add devices: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> I'm not sure I see the point in this driver.  Why can't you just
> register these devices directly from DT?

All these devices share the same bank of registers and we previously
used a single node. But with many devices sharing a single node, this is
problematic to register all the devices from DT. Using this MFD driver
to do it is a proper solution in this case.

To provide a regmap to the devices' drivers we also use syscon on the
chip/system controller nodes.

> > +MODULE_LICENSE("GPL");
> 
> v2

"GPL" is a valid choice, quoting include/linux.module.h:

	"GPL"              [GNU Public License v2 or later]
	"GPL v2"           [GNU Public License v2]

Is there a reason you explicitly want to use GPLv2, and only GPLv2?

Antoine

-- 
Antoine Ténart, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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