Re: [PATCH linux dev-4.16] drivers: i2c: master arbiter: create driver

[Guenter Roeck <linux@roeck-us.net>]

On 03/19/2018 05:45 AM, Peter Rosin wrote:
> Hi Ken,
> 
> Thanks for the patch!
> 
> I would have liked this subject:
> i2c: muxes: pca9641: new driver
> 
> On 2018-03-19 12:38, Ken Chen wrote:
>> Initial PCA9641 2 chennel I2C bus master arbiter
> 
> channel
> 
>> with separate implementation. It has probe issue
>> and difference device hehavior between PCA9541
> 
> behavior
> 
>> and PCA9641 in original PCA9641 patch.
>>
>> Signed-off-by: Ken Chen <chen.kenyy@inventec.com>
>> ---
>>   drivers/i2c/muxes/Kconfig           |   9 +
>>   drivers/i2c/muxes/Makefile          |   1 +
>>   drivers/i2c/muxes/i2c-mux-pca9641.c | 360 ++++++++++++++++++++++++++++++++++++
> 
> Given the big similarities between this and the pca9541 driver,
> I would very much prefer if you could extend that driver instead
> of making an almost-copy like this.
> 
> I have added some comments below anyway, but most of them are
> irrelevant given that I want this merged with the pca9541 driver.
> 
> But maybe Guenter feels differently about that merge?
> 

Same here. I didn't do a line-by-line comparison, but the code looks very similar.
I did look into the probe function searching for differences after noticing
"It has probe issue ...", but the difference there must be quite subtle since
I didn't find it. The only real difference seems to be arbitration, but that can
easily be added to the original driver as chip specific functions.

>>   3 files changed, 370 insertions(+)
>>   create mode 100644 drivers/i2c/muxes/i2c-mux-pca9641.c
>>
>> diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
>> index 52a4a92..f9c51b8 100644
>> --- a/drivers/i2c/muxes/Kconfig
>> +++ b/drivers/i2c/muxes/Kconfig
>> @@ -73,6 +73,15 @@ config I2C_MUX_PCA954x
>>   	  This driver can also be built as a module.  If so, the module
>>   	  will be called i2c-mux-pca954x.
>>   
>> +config I2C_MUX_PCA9641
>> +	tristate "NXP PCA9641 I2C Master demultiplexer"
>> +	help
>> +	  If you say yes here you get support for the NXP PCA9641
>> +	  I2C Master demultiplexer with an arbiter function.
>> +
>> +	  This driver can also be built as a module.  If so, the module
>> +	  will be called i2c-mux-pca9641.
>> +
>>   config I2C_MUX_PINCTRL
>>   	tristate "pinctrl-based I2C multiplexer"
>>   	depends on PINCTRL
>> diff --git a/drivers/i2c/muxes/Makefile b/drivers/i2c/muxes/Makefile
>> index 6d9d865..a229a1a 100644
>> --- a/drivers/i2c/muxes/Makefile
>> +++ b/drivers/i2c/muxes/Makefile
>> @@ -12,6 +12,7 @@ obj-$(CONFIG_I2C_MUX_LTC4306)	+= i2c-mux-ltc4306.o
>>   obj-$(CONFIG_I2C_MUX_MLXCPLD)	+= i2c-mux-mlxcpld.o
>>   obj-$(CONFIG_I2C_MUX_PCA9541)	+= i2c-mux-pca9541.o
>>   obj-$(CONFIG_I2C_MUX_PCA954x)	+= i2c-mux-pca954x.o
>> +obj-$(CONFIG_I2C_MUX_PCA9641)	+= i2c-mux-pca9641.o
>>   obj-$(CONFIG_I2C_MUX_PINCTRL)	+= i2c-mux-pinctrl.o
>>   obj-$(CONFIG_I2C_MUX_REG)	+= i2c-mux-reg.o
>>   
>> diff --git a/drivers/i2c/muxes/i2c-mux-pca9641.c b/drivers/i2c/muxes/i2c-mux-pca9641.c
>> new file mode 100644
>> index 0000000..bcf45c8
>> --- /dev/null
>> +++ b/drivers/i2c/muxes/i2c-mux-pca9641.c
>> @@ -0,0 +1,360 @@
>> +/*
>> + * I2C demultiplexer driver for PCA9641 bus master demultiplexer
>> + *
>> + * Copyright (c) 2010 Ericsson AB.
>> + *
>> + * Author: Ken Chen <chen.kenyy@inventec.com>
> 
> A bit rich to claim to be the sole author, when you clearly "just"
> modified the pca9541 driver. Please state the history!
> 

And while retaining the original copyright.

>> + *
>> + * Derived from:
> 
> Maybe you intended to add something here, but forgot?
> 
>> + *
>> + * 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.
>> + */

New files should use the SPDX license identifier.

>> +
>> +#include <linux/module.h>
>> +#include <linux/jiffies.h>
>> +#include <linux/delay.h>
>> +#include <linux/slab.h>
>> +#include <linux/device.h>
>> +#include <linux/i2c.h>
>> +#include <linux/i2c-mux.h>
>> +
>> +#include <linux/i2c/pca954x.h>
> 
> What is this last include for? We have moved away from specifying platform
> data in (new) code.
> 
>> +
>> +/*
>> + * The PCA9641 is two I2C bus masters demultiplexer. It supports two I2C masters
> 
> "is two I2C bus masters" -> "is a two I2C bus master"
> 
>> + * connected to a single slave bus.
>> + *
>> + * It is designed for high reliability dual master I2C bus applications where
>> + * correct system operation is required, even when two I2C master issue their
>> + * commands at the same time. The arbiter will select a winner and let it work
>> + * uninterrupted, and the losing master will take control of the I2C bus after
>> + * the winnter has finished. The arbiter also allows for queued requests where
> 
> winner
> 
>> + * a master requests the downstream bus while the other master has control.
>> + *
>> + */
>> +
>> +#define PCA9641_ID		0x01
>> +#define PCA9641_ID_MAGIC	0x38
>> +
>> +#define PCA9641_CONTROL		0x01
>> +#define PCA9641_STATUS		0x02
>> +#define PCA9641_TIME		0x03
>> +
>> +#define PCA9641_CTL_LOCK_REQ		BIT(0)
>> +#define PCA9641_CTL_LOCK_GRANT		BIT(1)
>> +#define PCA9641_CTL_BUS_CONNECT		BIT(2)
>> +#define PCA9641_CTL_BUS_INIT		BIT(3)
>> +#define PCA9641_CTL_SMBUS_SWRST		BIT(4)
>> +#define PCA9641_CTL_IDLE_TIMER_DIS	BIT(5)
>> +#define PCA9641_CTL_SMBUS_DIS		BIT(6)
>> +#define PCA9641_CTL_PRIORITY		BIT(7)
>> +
>> +#define PCA9641_STS_OTHER_LOCK		BIT(0)
>> +#define PCA9641_STS_BUS_INIT_FAIL	BIT(1)
>> +#define PCA9641_STS_BUS_HUNG		BIT(2)
>> +#define PCA9641_STS_MBOX_EMPTY		BIT(3)
>> +#define PCA9641_STS_MBOX_FULL		BIT(4)
>> +#define PCA9641_STS_TEST_INT		BIT(5)
>> +#define PCA9641_STS_SCL_IO		BIT(6)
>> +#define PCA9641_STS_SDA_IO		BIT(7)
>> +
>> +#define PCA9641_RES_TIME	0x03
>> +
>> +#define busoff(x, y)	(!((x) & PCA9641_CTL_LOCK_GRANT) && \
>> +			!((y) & PCA9641_STS_OTHER_LOCK))
>> +#define other_lock(x)	((x) & PCA9641_STS_OTHER_LOCK)
>> +#define lock_grant(x)	((x) & PCA9641_CTL_LOCK_GRANT)
>> +
>> +/* arbitration timeouts, in jiffies */
>> +#define ARB_TIMEOUT	(HZ / 8)	/* 125 ms until forcing bus ownership */
>> +#define ARB2_TIMEOUT	(HZ / 4)	/* 250 ms until acquisition failure */
>> +
>> +/* arbitration retry delays, in us */
>> +#define SELECT_DELAY_SHORT	50
>> +#define SELECT_DELAY_LONG	1000
>> +
>> +struct pca9641 {
>> +	struct i2c_client *client;
>> +	unsigned long select_timeout;
>> +	unsigned long arb_timeout;
>> +};
>> +
>> +static const struct i2c_device_id pca9641_id[] = {
>> +	{"pca9641", 0},
>> +	{}
>> +};
>> +
>> +MODULE_DEVICE_TABLE(i2c, pca9641_id);
>> +
>> +#ifdef CONFIG_OF
>> +static const struct of_device_id pca9641_of_match[] = {
>> +	{ .compatible = "nxp,pca9641" },
> 
> You need to describe the DT binding in Documentation/devicetree/bindings/i2c
> See nxp,pca9541.txt for inspiration.
> 
>> +	{}
>> +};
>> +#endif
>> +
>> +/*
>> + * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
>> + * as they will try to lock the adapter a second time.
>> + */
>> +static int pca9641_reg_write(struct i2c_client *client, u8 command, u8 val)
>> +{
>> +	struct i2c_adapter *adap = client->adapter;
>> +	int ret;
>> +
>> +	if (adap->algo->master_xfer) {
>> +		struct i2c_msg msg;
>> +		char buf[2];
>> +
>> +		msg.addr = client->addr;
>> +		msg.flags = 0;
>> +		msg.len = 2;
>> +		buf[0] = command;
>> +		buf[1] = val;
>> +		msg.buf = buf;
>> +		ret = __i2c_transfer(adap, &msg, 1);
>> +	} else {
>> +		union i2c_smbus_data data;
>> +
>> +		data.byte = val;
>> +		ret = adap->algo->smbus_xfer(adap, client->addr,
>> +					     client->flags,
>> +					     I2C_SMBUS_WRITE,
>> +					     command,
>> +					     I2C_SMBUS_BYTE_DATA, &data);
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +/*
>> + * Read from chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
>> + * as they will try to lock adapter a second time.
>> + */
>> +static int pca9641_reg_read(struct i2c_client *client, u8 command)
>> +{
>> +	struct i2c_adapter *adap = client->adapter;
>> +	int ret;
>> +	u8 val;
>> +
>> +	if (adap->algo->master_xfer) {
>> +		struct i2c_msg msg[2] = {
>> +			{
>> +				.addr = client->addr,
>> +				.flags = 0,
>> +				.len = 1,
>> +				.buf = &command
>> +			},
>> +			{
>> +				.addr = client->addr,
>> +				.flags = I2C_M_RD,
>> +				.len = 1,
>> +				.buf = &val
>> +			}
>> +		};
>> +		ret = __i2c_transfer(adap, msg, 2);
>> +		if (ret == 2)
>> +			ret = val;
>> +		else if (ret >= 0)
>> +			ret = -EIO;
>> +	} else {
>> +		union i2c_smbus_data data;
>> +
>> +		ret = adap->algo->smbus_xfer(adap, client->addr,
>> +					     client->flags,
>> +					     I2C_SMBUS_READ,
>> +					     command,
>> +					     I2C_SMBUS_BYTE_DATA, &data);
>> +		if (!ret)
>> +			ret = data.byte;
>> +	}
>> +	return ret;
>> +}
>> +
>> +/*
>> + * Arbitration management functions
>> + */
>> +static void pca9641_release_bus(struct i2c_client *client)
>> +{
>> +	pca9641_reg_write(client, PCA9641_CONTROL, 0);
>> +}
>> +
>> +/*
>> + * Channel arbitration
>> + *
>> + * Return values:
>> + *  <0: error
>> + *  0 : bus not acquired
>> + *  1 : bus acquired
>> + */
>> +static int pca9641_arbitrate(struct i2c_client *client)
>> +{
>> +	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
>> +	struct pca9641 *data = i2c_mux_priv(muxc);
>> +	int reg_ctl, reg_sts;
>> +
>> +	reg_ctl = pca9641_reg_read(client, PCA9641_CONTROL);
>> +	if (reg_ctl < 0)
>> +		return reg_ctl;
>> +	reg_sts = pca9641_reg_read(client, PCA9641_STATUS);
>> +
>> +	if (busoff(reg_ctl, reg_sts)) {
>> +		/*
>> +		 * Bus is off. Request ownership or turn it on unless
>> +		 * other master requested ownership.
>> +		 */
>> +		reg_ctl |= PCA9641_CTL_LOCK_REQ;
>> +		pca9641_reg_write(client, PCA9641_CONTROL, reg_ctl);
>> +		reg_ctl = pca9641_reg_read(client, PCA9641_CONTROL);
>> +
>> +		if (lock_grant(reg_ctl)) {
>> +			/*
>> +			 * Other master did not request ownership,
>> +			 * or arbitration timeout expired. Take the bus.
>> +			 */
>> +			reg_ctl |= PCA9641_CTL_BUS_CONNECT \
>> +					| PCA9641_CTL_LOCK_REQ;
>> +			pca9641_reg_write(client, PCA9641_CONTROL, reg_ctl);
>> +			data->select_timeout = SELECT_DELAY_SHORT;
>> +
>> +			return 1;
>> +		} else {
>> +			/*
>> +			 * Other master requested ownership.
>> +			 * Set extra long timeout to give it time to acquire it.
>> +			 */
>> +			data->select_timeout = SELECT_DELAY_LONG * 2;
>> +		}
>> +	} else if (lock_grant(reg_ctl)) {
>> +		/*
>> +		 * Bus is on, and we own it. We are done with acquisition.
>> +		 */
>> +		reg_ctl |= PCA9641_CTL_BUS_CONNECT | PCA9641_CTL_LOCK_REQ;
>> +		pca9641_reg_write(client, PCA9641_CONTROL, reg_ctl);
>> +
>> +		return 1;
>> +	} else if (other_lock(reg_sts)) {
>> +		/*
>> +		 * Other master owns the bus.
>> +		 * If arbitration timeout has expired, force ownership.
>> +		 * Otherwise request it.
>> +		 */
>> +		data->select_timeout = SELECT_DELAY_LONG;
>> +		reg_ctl |= PCA9641_CTL_LOCK_REQ;
>> +		pca9641_reg_write(client, PCA9641_CONTROL, reg_ctl);
>> +	}
>> +	return 0;
>> +}
>> +
>> +static int pca9641_select_chan(struct i2c_mux_core *muxc, u32 chan)
>> +{
>> +	struct pca9641 *data = i2c_mux_priv(muxc);
>> +	struct i2c_client *client = data->client;
>> +	int ret;
>> +	unsigned long timeout = jiffies + ARB2_TIMEOUT;
>> +		/* give up after this time */
>> +
>> +	data->arb_timeout = jiffies + ARB_TIMEOUT;
>> +		/* force bus ownership after this time */
>> +
>> +	do {
>> +		ret = pca9641_arbitrate(client);
>> +		if (ret)
>> +			return ret < 0 ? ret : 0;
>> +
>> +		if (data->select_timeout == SELECT_DELAY_SHORT)
>> +			udelay(data->select_timeout);
>> +		else
>> +			msleep(data->select_timeout / 1000);
>> +	} while (time_is_after_eq_jiffies(timeout));
>> +
>> +	return -ETIMEDOUT;
>> +}
>> +
>> +static int pca9641_release_chan(struct i2c_mux_core *muxc, u32 chan)
>> +{
>> +	struct pca9641 *data = i2c_mux_priv(muxc);
>> +	struct i2c_client *client = data->client;
>> +
>> +	pca9641_release_bus(client);
>> +	return 0;
>> +}
>> +
>> +/*
>> + * I2C init/probing/exit functions
>> + */
>> +static int pca9641_probe(struct i2c_client *client,
>> +			 const struct i2c_device_id *id)
>> +{
>> +	struct i2c_adapter *adap = client->adapter;
>> +	struct pca954x_platform_data *pdata = dev_get_platdata(&client->dev);
>> +	struct i2c_mux_core *muxc;
>> +	struct pca9641 *data;
>> +	int force;
>> +	int ret;
>> +
>> +	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
>> +		return -ENODEV;
> 
> Reading the data sheet, I noticed that the chip supports I2C device id.
> There's a brand new function available in -next [1] that allows you to
> check this. See the pca954x driver in -next for an example [2]. It checks
> the I2C device id for the newer pca984x chips.
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/i2c/i2c-core-base.c
> i2c_get_device_id(), currently circa line 2000
> 
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/i2c/muxes/i2c-mux-pca954x.c
> 
>> +	/*
>> +	 * I2C accesses are unprotected here.
>> +	 * We have to lock the adapter before releasing the bus.
>> +	 */
>> +	i2c_lock_adapter(adap);
>> +	pca9641_release_bus(client);
>> +	i2c_unlock_adapter(adap);
>> +
>> +	/* Create mux adapter */
>> +
>> +	force = 0;
>> +	if (pdata)
>> +		force = pdata->modes[0].adap_id;
>> +	muxc = i2c_mux_alloc(adap, &client->dev, 8, sizeof(*data),
> 
> Why 8? Should be 1, no?
> 
>> +			     I2C_MUX_ARBITRATOR,
>> +			     pca9641_select_chan, pca9641_release_chan);
>> +	if (!muxc)
>> +		return -ENOMEM;
>> +
>> +	data = i2c_mux_priv(muxc);
>> +	data->client = client;
>> +
>> +	i2c_set_clientdata(client, muxc);
>> +
>> +
> 
> Lose one of the empty lines here.
> 
>> +	ret = i2c_mux_add_adapter(muxc, force, 0, 0);
>> +	if (ret) {
>> +		dev_err(&client->dev, "failed to register master demultiplexer\n");
> 
> This dev_err should go. i2c_mux_add_adapter provides a more
> detailed error message on failure.
> 
> Cheers,
> Peter
> 
>> +		return ret;
>> +	}
>> +
>> +	dev_info(&client->dev, "registered master demultiplexer for I2C %s\n",
>> +		 client->name);
>> +
>> +	return 0;
>> +}
>> +
>> +static int pca9641_remove(struct i2c_client *client)
>> +{
>> +	struct i2c_mux_core *muxc = i2c_get_clientdata(client);
>> +
>> +	i2c_mux_del_adapters(muxc);
>> +	return 0;
>> +}
>> +
>> +static struct i2c_driver pca9641_driver = {
>> +	.driver = {
>> +		   .name = "pca9641",
>> +		   .of_match_table = of_match_ptr(pca9641_of_match),
>> +		   },
>> +	.probe = pca9641_probe,
>> +	.remove = pca9641_remove,
>> +	.id_table = pca9641_id,
>> +};
>> +
>> +module_i2c_driver(pca9641_driver);
>> +
>> +MODULE_AUTHOR("Ken Chen <chen.kenyy@inventec.com>");
>> +MODULE_DESCRIPTION("PCA9641 I2C master demultiplexer driver");
>> +MODULE_LICENSE("GPL v2");
>>
> 
>