linux-kernel - Re: [v3 03/10] mfd: mtk-mmsys: Add mmsys driver

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Date:   Mon, 25 Jun 2018 17:33:28 +0200
From:   Matthias Brugger <matthias.bgg@...il.com>
To:     Lee Jones <lee.jones@...aro.org>, matthias.bgg@...nel.org
Cc:     ulrich.hecht+renesas@...il.com, laurent.pinchart@...asonboard.com,
        ck.hu@...iatek.com, p.zabel@...gutronix.de, airlied@...ux.ie,
        robh+dt@...nel.org, mark.rutland@....com, mturquette@...libre.com,
        sboyd@...eaurora.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, mchehab@...nel.org,
        rdunlap@...radead.org, sean.wang@...iatek.com,
        linux-clk@...r.kernel.org, linux@...linux.org.uk,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Matthias Brugger <mbrugger@...e.com>
Subject: Re: [v3 03/10] mfd: mtk-mmsys: Add mmsys driver



On 30/04/18 12:18, Lee Jones wrote:
> On Fri, 27 Apr 2018, matthias.bgg@...nel.org wrote:
> 
>> From: Matthias Brugger <mbrugger@...e.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@...e.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@...il.com>
>> + *
>> + * Author: Matthias Brugger <matthias.bgg@...il.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.

Regards,
Matthias