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Subject: Re: [v3 03/10] mfd: mtk-mmsys: Add mmsys driver
To:     Lee Jones <lee.jones@linaro.org>,
        Matthias Brugger <matthias.bgg@gmail.com>
Cc:     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
References: <cover.1524820923.git.mbrugger@suse.com>
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From:   Matthias Brugger <mbrugger@suse.com>
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Message-ID: <b6301691-a9f6-64fe-dd8a-ffe51fad6799@suse.com>
Date:   Wed, 4 Jul 2018 18:17:35 +0200
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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.

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.

Regards,
Matthias