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Date:   Wed, 4 Jul 2018 17:45:40 +0100
From:   Lee Jones <lee.jones@linaro.org>
To:     Matthias Brugger <mbrugger@suse.com>
Cc:     Matthias Brugger <matthias.bgg@gmail.com>, matthias.bgg@kernel.org,
        ulrich.hecht+renesas@gmail.com, laurent.pinchart@ideasonboard.com,
        ck.hu@mediatek.com, p.zabel@pengutronix.de, airlied@linux.ie,
        robh+dt@kernel.org, mark.rutland@arm.com, mturquette@baylibre.com,
        sboyd@codeaurora.org, davem@davemloft.net,
        gregkh@linuxfoundation.org, mchehab@kernel.org,
        rdunlap@infradead.org, sean.wang@mediatek.com,
        linux-clk@vger.kernel.org, linux@armlinux.org.uk,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
Subject: Re: [v3 03/10] mfd: mtk-mmsys: Add mmsys driver
Message-ID: <20180704164540.GH496@dell>
References: <cover.1524820923.git.mbrugger@suse.com>
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On Wed, 04 Jul 2018, Matthias Brugger wrote:

> 
> 
> On 03/07/18 09:11, Lee Jones wrote:
> > On Mon, 25 Jun 2018, Matthias Brugger wrote:
> >> On 30/04/18 12:18, Lee Jones wrote:
> >>> On Fri, 27 Apr 2018, matthias.bgg@kernel.org wrote:
> >>>
> >>>> From: Matthias Brugger <mbrugger@suse.com>
> >>>>
> >>>> The MMSYS subsystem includes clocks and drm components.
> >>>> This patch adds a MFD device to probe both drivers from the same
> >>>> device tree compatible.
> >>>>
> >>>> Signed-off-by: Matthias Brugger <mbrugger@suse.com>
> >>>> ---
> >>>>  drivers/mfd/Kconfig     |  9 ++++++
> >>>>  drivers/mfd/Makefile    |  2 ++
> >>>>  drivers/mfd/mtk-mmsys.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++
> >>>>  3 files changed, 90 insertions(+)
> >>>>  create mode 100644 drivers/mfd/mtk-mmsys.c
> >>>>
> >>>> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> >>>> index b860eb5aa194..d23a3b9a2c58 100644
> >>>> --- a/drivers/mfd/Kconfig
> >>>> +++ b/drivers/mfd/Kconfig
> >>>> @@ -378,6 +378,15 @@ config MFD_MC13XXX_I2C
> >>>>  	help
> >>>>  	  Select this if your MC13xxx is connected via an I2C bus.
> >>>>  
> >>>> +config MFD_MEDIATEK_MMSYS
> >>>> +	tristate "Mediatek MMSYS interface"
> >>>> +	select MFD_CORE
> >>>> +	select REGMAP_MMIO
> >>>> +	help
> >>>> +	  Select this if you have a MMSYS subsystem in your SoC. The
> >>>> +	  MMSYS subsystem has at least a clock driver part and some
> >>>> +	  DRM components.
> >>>> +
> >>>>  config MFD_MXS_LRADC
> >>>>  	tristate "Freescale i.MX23/i.MX28 LRADC"
> >>>>  	depends on ARCH_MXS || COMPILE_TEST
> >>>> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> >>>> index d9d2cf0d32ef..b96118bd68d9 100644
> >>>> --- a/drivers/mfd/Makefile
> >>>> +++ b/drivers/mfd/Makefile
> >>>> @@ -98,6 +98,8 @@ obj-$(CONFIG_MFD_MC13XXX)	+= mc13xxx-core.o
> >>>>  obj-$(CONFIG_MFD_MC13XXX_SPI)	+= mc13xxx-spi.o
> >>>>  obj-$(CONFIG_MFD_MC13XXX_I2C)	+= mc13xxx-i2c.o
> >>>>  
> >>>> +obj-$(CONFIG_MFD_MEDIATEK_MMSYS) += mtk-mmsys.o
> >>>> +
> >>>>  obj-$(CONFIG_MFD_CORE)		+= mfd-core.o
> >>>>  
> >>>>  obj-$(CONFIG_EZX_PCAP)		+= ezx-pcap.o
> >>>> diff --git a/drivers/mfd/mtk-mmsys.c b/drivers/mfd/mtk-mmsys.c
> >>>> new file mode 100644
> >>>> index 000000000000..c802343fb1c6
> >>>> --- /dev/null
> >>>> +++ b/drivers/mfd/mtk-mmsys.c
> >>>> @@ -0,0 +1,79 @@
> >>>> +// SPDX-License-Identifier: GPL-2.0+
> >>>> +
> >>>> +/*
> >>>> + * mtk-mmsys.c -- Mediatek MMSYS multi-function driver
> >>>> + *
> >>>> + * Copyright (c) 2018 Matthias Brugger <matthias.bgg@gmail.com>
> >>>> + *
> >>>> + * Author: Matthias Brugger <matthias.bgg@gmail.com>
> >>>> + */
> >>>> +
> >>>> +#include <linux/module.h>
> >>>> +#include <linux/init.h>
> >>>> +#include <linux/mfd/core.h>
> >>>> +#include <linux/of.h>
> >>>> +#include <linux/of_address.h>
> >>>> +#include <linux/of_device.h>
> >>>> +#include <linux/platform_device.h>
> >>>> +#include <linux/regmap.h>
> >>>> +
> >>>> +enum {
> >>>> +	MMSYS_MT2701 = 1,
> >>>> +};
> >>>> +
> >>>> +static const struct mfd_cell mmsys_mt2701_devs[] = {
> >>>> +	{ .name = "clk-mt2701-mm", },
> >>>> +	{ .name = "drm-mt2701-mm", },
> >>>> +};
> >>>> +
> >>>> +static int mmsys_probe(struct platform_device *pdev)
> >>>> +{
> >>>> +	const struct mfd_cell *mmsys_cells;
> >>>> +	int nr_cells;
> >>>> +	long id;
> >>>> +	int ret;
> >>>> +
> >>>> +	id = (long) of_device_get_match_data(&pdev->dev);
> >>>> +	if (!id) {
> >>>> +		dev_err(&pdev->dev, "of_device_get match_data() failed\n");
> >>>> +		return -EINVAL;
> >>>> +	}
> >>>> +
> >>>> +	switch (id) {
> >>>> +	case MMSYS_MT2701:
> >>>> +		mmsys_cells = mmsys_mt2701_devs;
> >>>> +		nr_cells = ARRAY_SIZE(mmsys_mt2701_devs);
> >>>> +		break;
> >>>> +	default:
> >>>> +		return -ENODEV;
> >>>> +	}
> >>>> +
> >>>> +	ret = devm_mfd_add_devices(&pdev->dev, 0, mmsys_cells, nr_cells,
> >>>> +					NULL, 0, NULL);
> >>>> +	if (ret) {
> >>>> +		dev_err(&pdev->dev, "failed to add MFD devices %d\n", ret);
> >>>> +		return ret;
> >>>> +	}
> >>>> +
> >>>> +	return 0;
> >>>> +};
> >>>
> >>> This driver is pretty pointless.  It doesn't actually do anything.
> >>>
> >>> I think you just want to use "simple-mfd" instead.
> >>>
> >>
> >> I think the problem is, that right now we have two drivers which use the same
> >> devicetree binding, which are clk and drm driver. With a simple-mfd we would
> >> need two compatibles, and this would break backwards compatibility.
> > 
> > So what functionality does this driver provide you with that you do
> > not have currently?
> > 
> 
> I'm not sure if I get your question. Point is, that the MMSYS implementation for
> mt8173 is broken, as it assumes that we can probe two drivers with the
> mediatek,mt8173-mmsys compatible. Somehow it used to work, but from what I
> understand it was a bug. So older devicetrees use just on mt8173-mmsys
> compatible in ther DTB.

Okay, that is what I was getting at.  Thanks for the explanation.

Do you have a datasheet I can look at?

> I would like to keep backwards compatibility for the device tree, that's why I
> was searching for a solution where we can probe two drivers and came up with
> this mfd solution.
>
> So no new functionality, the clk driver provides the clock the drm components need.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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