Message-ID: <20140510011659.GH7047@lukather>
Date:	Fri, 9 May 2014 20:16:59 -0500
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Boris BREZILLON <boris.brezillon@...e-electrons.com>
Cc:	Wolfram Sang <wsa@...-dreams.de>,
	Randy Dunlap <rdunlap@...radead.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Shuge <shuge@...winnertech.com>, kevin@...winnertech.com,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] i2c: sunxi: add P2WI (Push/Pull 2 Wire Interface)
 controller support

On Fri, May 09, 2014 at 06:56:10PM +0200, Boris BREZILLON wrote:
> The P2WI looks like an SMBus controller which only supports byte data
> transfers. But, it differs from standard SMBus protocol on several
> aspects:
> - it supports only one slave device, and thus drop the address field
> - it adds a parity bit every 8bits of data
> - only one read access is required to read a byte (instead of a read
>   followed by a write access in standard SMBus protocol)
> - there's no Ack bit after each byte transfer
> 
> This means this bus cannot be used to interface with standard SMBus
> devices (the only known device to support this interface is the AXP221
> PMIC).
> 
> Signed-off-by: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> ---
> Changes since v2:
> - drop the initialization (switch from I2C to P2WI mode) part
> - print devm_ioremap_resource err code

You'll also need to update the documentation of the DT bindings.

> 
>  drivers/i2c/busses/Kconfig          |  12 ++
>  drivers/i2c/busses/Makefile         |   1 +
>  drivers/i2c/busses/i2c-sun6i-p2wi.c | 352 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 365 insertions(+)
>  create mode 100644 drivers/i2c/busses/i2c-sun6i-p2wi.c
> 
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index c94db1c..09bce1c 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -771,6 +771,18 @@ config I2C_STU300
>  	  This driver can also be built as a module. If so, the module
>  	  will be called i2c-stu300.
>  
> +config I2C_SUN6I_P2WI
> +	tristate "Allwinner sun6i internal P2WI controller"
> +	depends on ARCH_SUNXI
> +	help
> +	  If you say yes to this option, support will be included for the
> +	  P2WI (Push/Pull 2 Wire Interface) controller embedded in some sunxi
> +	  SOCs.
> +	  The P2WI looks like an SMBus controller (which supports only byte
> +	  accesses), except that it only supports one slave device.
> +	  This interface is used to connect to specific PMIC devices (like the
> +	  AXP221).
> +
>  config I2C_TEGRA
>  	tristate "NVIDIA Tegra internal I2C controller"
>  	depends on ARCH_TEGRA
> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
> index 18d18ff..58feeb9 100644
> --- a/drivers/i2c/busses/Makefile
> +++ b/drivers/i2c/busses/Makefile
> @@ -75,6 +75,7 @@ obj-$(CONFIG_I2C_SIMTEC)	+= i2c-simtec.o
>  obj-$(CONFIG_I2C_SIRF)		+= i2c-sirf.o
>  obj-$(CONFIG_I2C_ST)		+= i2c-st.o
>  obj-$(CONFIG_I2C_STU300)	+= i2c-stu300.o
> +obj-$(CONFIG_I2C_SUN6I_P2WI)	+= i2c-sun6i-p2wi.o
>  obj-$(CONFIG_I2C_TEGRA)		+= i2c-tegra.o
>  obj-$(CONFIG_I2C_VERSATILE)	+= i2c-versatile.o
>  obj-$(CONFIG_I2C_WMT)		+= i2c-wmt.o
> diff --git a/drivers/i2c/busses/i2c-sun6i-p2wi.c b/drivers/i2c/busses/i2c-sun6i-p2wi.c
> new file mode 100644
> index 0000000..7c859ee
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-sun6i-p2wi.c
> @@ -0,0 +1,352 @@
> +/*
> + * P2WI (Push-Pull Two Wire Interface) bus driver.
> + *
> + * Author: Boris BREZILLON <boris.brezillon@...e-electrons.com>
> + *
> + * This file is licensed under the terms of the GNU General Public License
> + * version 2.  This program is licensed "as is" without any warranty of any
> + * kind, whether express or implied.
> + */
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/module.h>
> +#include <linux/spinlock.h>
> +#include <linux/i2c.h>
> +#include <linux/interrupt.h>
> +#include <linux/platform_device.h>
> +#include <linux/io.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/of_irq.h>
> +#include <linux/clk.h>
> +#include <linux/err.h>
> +#include <linux/delay.h>
> +#include <linux/clk.h>
> +#include <linux/reset.h>
> +
> +
> +/* P2WI registers */
> +#define P2WI_CTRL		0x0
> +#define P2WI_CCR		0x4
> +#define P2WI_INTE		0x8
> +#define P2WI_INTS		0xc
> +#define P2WI_DADDR0		0x10
> +#define P2WI_DADDR1		0x14
> +#define P2WI_DLEN		0x18
> +#define P2WI_DATA0		0x1c
> +#define P2WI_DATA1		0x20
> +#define P2WI_LCR		0x24
> +#define P2WI_PMCR		0x28
> +
> +/* CTRL fields */
> +#define P2WI_CTRL_START_TRANS		BIT(7)
> +#define P2WI_CTRL_ABORT_TRANS		BIT(6)
> +#define P2WI_CTRL_GLOBAL_INT_ENB	BIT(1)
> +#define P2WI_CTRL_SOFT_RST		BIT(0)
> +
> +/* CLK CTRL fields */
> +#define P2WI_CCR_SDA_OUT_DELAY(v)	(((v) & 0x7) << 8)
> +#define P2WI_CCR_MAX_CLK_DIV		0xff
> +#define P2WI_CCR_CLK_DIV(v)		((v) & P2WI_CCR_MAX_CLK_DIV)
> +
> +/* STATUS fields */
> +#define P2WI_INTS_TRANS_ERR_ID(v)	(((v) >> 8) & 0xff)
> +#define P2WI_INTS_LOAD_BSY		BIT(2)
> +#define P2WI_INTS_TRANS_ERR		BIT(1)
> +#define P2WI_INTS_TRANS_OVER		BIT(0)
> +
> +/* DATA LENGTH fields*/
> +#define P2WI_DLEN_READ			BIT(4)
> +#define P2WI_DLEN_DATA_LENGTH(v)	((v - 1) & 0x7)
> +
> +/* LINE CTRL fields*/
> +#define P2WI_LCR_SCL_STATE		BIT(5)
> +#define P2WI_LCR_SDA_STATE		BIT(4)
> +#define P2WI_LCR_SCL_CTL		BIT(3)
> +#define P2WI_LCR_SCL_CTL_EN		BIT(2)
> +#define P2WI_LCR_SDA_CTL		BIT(1)
> +#define P2WI_LCR_SDA_CTL_EN		BIT(0)
> +
> +/* PMU MODE CTRL fields */
> +#define P2WI_PMCR_PMU_INIT_SEND		BIT(31)
> +#define P2WI_PMCR_PMU_INIT_DATA(v)	(((v) & 0xff) << 16)
> +#define P2WI_PMCR_PMU_MODE_REG(v)	(((v) & 0xff) << 8)
> +#define P2WI_PMCR_PMU_DEV_ADDR(v)	((v) & 0xff)
> +
> +#define P2WI_MAX_FREQ			6000000
> +
> +struct p2wi {
> +	struct i2c_adapter adapter;
> +	struct completion complete;
> +	unsigned int irq;
> +	unsigned int status;
> +	void __iomem *regs;
> +	struct clk *clk;
> +	struct reset_control *rstc;
> +	int slave_addr;
> +};
> +
> +static irqreturn_t p2wi_interrupt(int irq, void *dev_id)
> +{
> +	struct p2wi *p2wi = dev_id;
> +	unsigned long status;
> +
> +	status = readl(p2wi->regs + P2WI_INTS);
> +	p2wi->status = status;
> +
> +	/* Clear interrupts */
> +	status &= (P2WI_INTS_LOAD_BSY | P2WI_INTS_TRANS_ERR |
> +		   P2WI_INTS_TRANS_OVER);
> +	writel(status, p2wi->regs + P2WI_INTS);
> +
> +	complete(&p2wi->complete);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static u32 p2wi_functionality(struct i2c_adapter *adap)
> +{
> +	return I2C_FUNC_SMBUS_BYTE_DATA;
> +}
> +
> +static int p2wi_smbus_xfer(struct i2c_adapter *adap, u16 addr,
> +			   unsigned short flags, char read_write,
> +			   u8 command, int size, union i2c_smbus_data *data)
> +{
> +	struct p2wi *p2wi = i2c_get_adapdata(adap);
> +	unsigned long dlen = P2WI_DLEN_DATA_LENGTH(1);
> +
> +	if (addr > 0xff ||
> +	    (p2wi->slave_addr >= 0 && addr != p2wi->slave_addr)) {
> +		dev_err(&adap->dev, "invalid P2WI address\n");
> +		return -EINVAL;
> +	}
> +
> +	if (!data)
> +		return -EINVAL;
> +
> +	writel(command, p2wi->regs + P2WI_DADDR0);
> +
> +	if (read_write == I2C_SMBUS_READ)
> +		dlen |= P2WI_DLEN_READ;
> +	else
> +		writel(data->byte, p2wi->regs + P2WI_DATA0);
> +
> +	writel(dlen, p2wi->regs + P2WI_DLEN);
> +
> +	if (readl(p2wi->regs + P2WI_CTRL) & P2WI_CTRL_START_TRANS) {
> +		dev_err(&adap->dev, "P2WI bus busy\n");
> +		return -EBUSY;
> +	}
> +
> +	reinit_completion(&p2wi->complete);
> +
> +	writel(P2WI_INTS_LOAD_BSY | P2WI_INTS_TRANS_ERR | P2WI_INTS_TRANS_OVER,
> +	       p2wi->regs + P2WI_INTE);
> +
> +	writel(P2WI_CTRL_START_TRANS | P2WI_CTRL_GLOBAL_INT_ENB,
> +	       p2wi->regs + P2WI_CTRL);
> +
> +	wait_for_completion(&p2wi->complete);
> +
> +	if (p2wi->status & P2WI_INTS_LOAD_BSY) {
> +		dev_err(&adap->dev, "P2WI bus busy\n");
> +		return -EBUSY;
> +	}
> +
> +	if (p2wi->status & P2WI_INTS_TRANS_ERR) {
> +		dev_err(&adap->dev, "P2WI bus xfer error\n");
> +		return -ENXIO;
> +	}
> +
> +	if (read_write == I2C_SMBUS_READ)
> +		data->byte = readl(p2wi->regs + P2WI_DATA0);
> +
> +	return 0;
> +}
> +
> +static const struct i2c_algorithm p2wi_algo = {
> +	.smbus_xfer = p2wi_smbus_xfer,
> +	.functionality = p2wi_functionality,
> +};
> +
> +static const struct of_device_id p2wi_of_match_table[] = {
> +	{ .compatible = "allwinner,sun6i-a31-p2wi" },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, p2wi_of_match_table);
> +
> +static int p2wi_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_node *np = dev->of_node;
> +	struct device_node *childnp;
> +	unsigned long parent_clk_freq;
> +	u32 clk_freq = 100000;
> +	struct resource *r;
> +	struct p2wi *p2wi;
> +	u32 slave_addr;
> +	int clk_div;
> +	int ret;
> +
> +	of_property_read_u32(np, "clock-frequency", &clk_freq);
> +	if (clk_freq > P2WI_MAX_FREQ) {
> +		dev_err(dev,
> +			"required clock-frequency (%u Hz) is too high (max = 6MHz)",
> +			clk_freq);
> +		return -EINVAL;
> +	}
> +
> +	if (of_get_child_count(np) > 1) {
> +		dev_err(dev, "P2WI only supports one slave device\n");
> +		return -EINVAL;
> +	}

If you return whenever you have more than one child here...

> +	p2wi = devm_kzalloc(dev, sizeof(struct p2wi), GFP_KERNEL);
> +	if (!p2wi) {
> +		dev_err(dev, "failed to allocate p2wi struct\n");
> +		return -ENOMEM;
> +	}
> +
> +	p2wi->slave_addr = -1;
> +
> +	/*
> +	 * Authorize a p2wi node without any children to be able to use an
> +	 * i2c-dev from userpace.
> +	 * In this case the slave_addr is set to -1 and won't be checked when
> +	 * launching a P2WI transfer.
> +	 *
> +	 * If the p2wi node contains more than one child, the first one will
> +	 * be considered as the only slave node.

... how does the second part of this comment make any sense? You won't
even get there in such a case.

Thanks,
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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