Re: [PATCH linux-next 2/2] mfd: flexcom: add a driver for Atmel Flexible Serial Communication Unit

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Mon, 15 Jun 2015 18:38:05 +0200
Cyrille Pitchen <cyrille.pitchen@atmel.com> wrote:

> This driver supports the new Atmel Flexcom. The Flexcom is a wrapper which
> integrates one SPI controller, one I2C controller and one USART. Only one
> function can be enabled at a time. This driver selects the function once
> for all, when the Flexcom is probed, according to the value of the new
> "atmel,flexcom-mode" device tree property.
> 
> This driver has chosen to present the Flexcom to the system as a MFD so
> the implementation is seamless for the existing Atmel SPI, I2C and USART
> drivers.
> 
> Also the Flexcom embeds FIFOs: the latest patches of the SPI, I2C and
> USART drivers take advantage of this new feature.
> 
> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> ---
>  drivers/mfd/Kconfig         | 11 +++++
>  drivers/mfd/Makefile        |  1 +
>  drivers/mfd/atmel-flexcom.c | 97 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 109 insertions(+)
>  create mode 100644 drivers/mfd/atmel-flexcom.c
> 
> diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> index aefbbbf..4aebf08 100644
> --- a/drivers/mfd/Kconfig
> +++ b/drivers/mfd/Kconfig
> @@ -60,6 +60,17 @@ config MFD_AAT2870_CORE
>  	  additional drivers must be enabled in order to use the
>  	  functionality of the device.
>  
> +config MFD_ATMEL_FLEXCOM
> +	tristate "Atmel Flexcom (Flexible Serial Communication Unit)"
> +	select MFD_CORE
> +	depends on OF
> +	help
> +	  Select this to get support for Atmel Flexcom. This is a wrapper
> +	  which embeds a SPI controller, a I2C controller and a USART. Only
> +	  one function can be used at a time. The choice is done at boot time
> +	  by the probe function of this MFD driver according to a device tree
> +	  property.
> +
>  config MFD_ATMEL_HLCDC
>  	tristate "Atmel HLCDC (High-end LCD Controller)"
>  	select MFD_CORE
> diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> index ea40e07..0705eb2 100644
> --- a/drivers/mfd/Makefile
> +++ b/drivers/mfd/Makefile
> @@ -160,6 +160,7 @@ obj-$(CONFIG_MFD_SPMI_PMIC)	+= qcom-spmi-pmic.o
>  obj-$(CONFIG_TPS65911_COMPARATOR)	+= tps65911-comparator.o
>  obj-$(CONFIG_MFD_TPS65090)	+= tps65090.o
>  obj-$(CONFIG_MFD_AAT2870_CORE)	+= aat2870-core.o
> +obj-$(CONFIG_MFD_ATMEL_FLEXCOM)	+= atmel-flexcom.o
>  obj-$(CONFIG_MFD_ATMEL_HLCDC)	+= atmel-hlcdc.o
>  obj-$(CONFIG_MFD_INTEL_MSIC)	+= intel_msic.o
>  obj-$(CONFIG_MFD_PALMAS)	+= palmas.o
> diff --git a/drivers/mfd/atmel-flexcom.c b/drivers/mfd/atmel-flexcom.c
> new file mode 100644
> index 0000000..14c35e6
> --- /dev/null
> +++ b/drivers/mfd/atmel-flexcom.c
> @@ -0,0 +1,97 @@
> +/*
> + * Driver for Atmel Flexcom
> + *
> + * Copyright (C) 2015 Atmel Corporation
> + *
> + * Author: Cyrille Pitchen <cyrille.pitchen@atmel.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + */
> +
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/kernel.h>
> +#include <linux/platform_device.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/clk.h>
> +
> +#define FX_MR		0x0
> +#define FX_RHR		0x10
> +#define FX_THR		0x20
> +#define FX_VERSION	0xfc
> +
> +#define FX_MR_NO_COM	0
> +#define FX_MR_USART	1
> +#define FX_MR_SPI	2
> +#define FX_MR_TWI	3
> +
> +
> +static int atmel_flexcom_probe(struct platform_device *pdev)
> +{
> +	struct clk *clk;
> +	struct resource *res;
> +	unsigned char __iomem *map;
> +	unsigned int version, mr;
> +	const char *mode;
> +	int err;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	map = devm_ioremap_resource(&pdev->dev, res);

If you take the approach I suggested in the DT binding review,
you shouldn't reserve the whole memory region, just the flexcom
part(0x0 to 0x200). 

> +	if (IS_ERR(map))
> +		return PTR_ERR(map);
> +
> +	clk = devm_clk_get(&pdev->dev, NULL);
> +	if (IS_ERR(clk))
> +		return PTR_ERR(clk);
> +
> +	err = of_property_read_string(pdev->dev.of_node,
> +				      "atmel,flexcom-mode", &mode);
> +	if (err)
> +		return err;
> +
> +	if (!strcmp(mode, "usart"))
> +		mr = FX_MR_USART;
> +	else if (!strcmp(mode, "spi"))
> +		mr = FX_MR_SPI;
> +	else if (!strcmp(mode, "twi") || !strcmp(mode, "i2c"))
> +		mr = FX_MR_TWI;
> +	else
> +		return -EINVAL;
> +
> +	clk_prepare_enable(clk);
> +	version = __raw_readl(map + FX_VERSION);
> +	__raw_writel(mr, map + FX_MR);
> +	clk_disable_unprepare(clk);

Is there a good reason to use the __raw versions of the writel/readl
functions ?



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com