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Subject: Re: [v3 03/10] mfd: mtk-mmsys: Add mmsys driver
To:     Lee Jones <lee.jones@linaro.org>
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
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From:   Matthias Brugger <mbrugger@suse.com>
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Message-ID: <92a851a9-a12c-e773-5f43-007f4d08b7e3@suse.com>
Date:   Thu, 5 Jul 2018 13:25:27 +0200
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On 04/07/18 18:45, Lee Jones wrote:
> 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?
> 

Unfortunately there is no datasheet you can get without a NDA. The only public
available information I'm aware of is for the (not upstream supported) 96board
[1]. And it's only the register description. You can find some more explanation
about the MMSYS in older threads which tried to solve the very same problem [2]

Regards,
Matthias


[1]
https://www.96boards.org/documentation/consumer/mediatekx20/additional-docs/docs/MT6797_Register_Table_Part_2.pdf
[2] http://lists.infradead.org/pipermail/linux-mediatek/2017-October/010979.html

>> 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.
>