Date:   Wed, 11 Apr 2018 11:37:11 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Ken Chen <chen.kenyy@...entec.com>
Cc:     linux-kernel@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        Wolfram Sang <wsa@...-dreams.de>, joel@....id.au,
        linux-i2c@...r.kernel.org
Subject: Re: [PATCH linux dev-4.16 v2] i2c: muxes: pca9641: new driver

Hi Ken,

It's been a couple of weeks and I wondered if you are making any
progress? Simple lack of time perhaps, or are you stuck and need
help?

Cheers,
Peter

On 2018-03-20 10:31, Peter Rosin wrote:
> On 2018-03-20 07:19, Ken Chen wrote:
>> Signed-off-by: Ken Chen <chen.kenyy@...entec.com>
> 
> Ok, now that you are not adding a new driver, but instead
> modify an existing driver, the subject I requested in no
> longer relevant. Now I would like to see:
> 
> i2c: mux: pca9541: add support for PCA9641 chips
> 
> Or something like that.
> 
>> ---
>> v1->v2
>> - Merged PCA9641 code into i2c-mux-pca9541.c
>> - Modified title
>> - Add PCA9641 detect function
>> ---
>>  drivers/i2c/muxes/i2c-mux-pca9541.c | 184 ++++++++++++++++++++++++++++++++++--
>>  1 file changed, 174 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/i2c/muxes/i2c-mux-pca9541.c b/drivers/i2c/muxes/i2c-mux-pca9541.c
>> index 6a39ada..493f947 100644
>> --- a/drivers/i2c/muxes/i2c-mux-pca9541.c
>> +++ b/drivers/i2c/muxes/i2c-mux-pca9541.c
>> @@ -1,5 +1,5 @@
>>  /*
>> - * I2C multiplexer driver for PCA9541 bus master selector
>> + * I2C multiplexer driver for PCA9541/PCA9641 bus master selector
>>   *
>>   * Copyright (c) 2010 Ericsson AB.
>>   *
>> @@ -26,8 +26,8 @@
>>  #include <linux/slab.h>
>>  
>>  /*
>> - * The PCA9541 is a bus master selector. It supports two I2C masters connected
>> - * to a single slave bus.
>> + * The PCA9541/PCA9641 is a bus master selector. It supports two I2C masters 
> 
> PCA9541 and PCA9641 are bus master selectors. They support two I2C masters
> 
> And make sure to lose the trailing space.
> 
>> + * connected to a single slave bus.
>>   *
>>   * Before each bus transaction, a master has to acquire bus ownership. After the
>>   * transaction is complete, bus ownership has to be released. This fits well
>> @@ -58,11 +58,43 @@
>>  #define PCA9541_ISTAT_MYTEST	(1 << 6)
>>  #define PCA9541_ISTAT_NMYTEST	(1 << 7)
>>  
>> +#define PCA9641_ID		0x00
>> +#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 BUSON		(PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
>>  #define MYBUS		(PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
>>  #define mybus(x)	(!((x) & MYBUS) || ((x) & MYBUS) == MYBUS)
>>  #define busoff(x)	(!((x) & BUSON) || ((x) & BUSON) == BUSON)
>>  
>> +#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)
> These macro names are now completely hideous. They were bad before,
> but this is just too much for me. So, instead of adding BUSOFF etc,
> I would like to see all the macros with a chip prefix. But I think
> they will get overly long, so I think you should just write trivial
> pca9541_mybus, pca9541_busoff, pca9641_busoff etc functions. The
> compiler should inline them just fine.
> 
> The rename of the existing macros and their conversion to functions
> should be in the first preparatory patch that I mention below. The
> new functions should be in the second patch.
> 
>> +
>>  /* 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 */
>> @@ -79,6 +111,7 @@ struct pca9541 {
>>  
>>  static const struct i2c_device_id pca9541_id[] = {
>>  	{"pca9541", 0},
>> +	{"pca9641", 1},
> 
> You are actually not using this 0/1 difference. Have a look at
> e.g. how the i2c-mux-pca954x driver uses this as an index into
> a chip description array. I would like to see something similar
> here...
> 
>>  	{}
>>  };
>>  
>> @@ -87,6 +120,7 @@ MODULE_DEVICE_TABLE(i2c, pca9541_id);
>>  #ifdef CONFIG_OF
>>  static const struct of_device_id pca9541_of_match[] = {
>>  	{ .compatible = "nxp,pca9541" },
>> +	{ .compatible = "nxp,pca9641" },
> 
> ...including pointers to the above chip descriptions here, just
> like the pca954x driver.
> 
>>  	{}
>>  };
>>  MODULE_DEVICE_TABLE(of, pca9541_of_match);
>> @@ -328,6 +362,125 @@ static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
>>  }
>>  
>>  /*
>> + * Arbitration management functions
>> + */
>> +static void pca9641_release_bus(struct i2c_client *client)
>> +{
>> +	pca9541_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 pca9541 *data = i2c_mux_priv(muxc);
>> +	int reg_ctl, reg_sts;
>> +
>> +	reg_ctl = pca9541_reg_read(client, PCA9641_CONTROL);
>> +	if (reg_ctl < 0)
>> +		return reg_ctl;
>> +	reg_sts = pca9541_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;
>> +		pca9541_reg_write(client, PCA9641_CONTROL, reg_ctl);
>> +		reg_ctl = pca9541_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;
>> +			pca9541_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;
>> +		pca9541_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;
>> +		pca9541_reg_write(client, PCA9641_CONTROL, reg_ctl);
>> +	}
>> +	return 0;
>> +}
>> +
>> +static int pca9641_select_chan(struct i2c_mux_core *muxc, u32 chan)
>> +{
>> +	struct pca9541 *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 pca9541 *data = i2c_mux_priv(muxc);
>> +	struct i2c_client *client = data->client;
>> +
>> +	pca9641_release_bus(client);
>> +	return 0;
>> +}
> 
> The pca9641_select_chan and pca9641_release_chan functions are exact
> copies of the pca9541 counterparts, with the exception of which
> functions they ultimately call. So, instead of using different
> function pointers in the i2c_mux_alloc calls below, add a couple of
> function pointers to the above mentioned chip description struct.
> 
> Then change pca9541_release_chan to something like this:
> 
> static int pca9541_release_chan(struct i2c_mux_core *muxc, u32 chan)
> {
> 	struct pca9541 *data = i2c_mux_priv(muxc);
> 	struct i2c_client *client = data->client;
> 
> 	data->chip->release_bus(client);
> 	return 0;
> }
> 
> Similarly for the *_select_chan "wrapper".
> 
> Now, these changes will somewhat affect the pca9541 side of the
> driver, so I would like to see more than one patch. There should be
> patches that prepares the driver that should be kind of easy to
> verify that they are equivalent but that makes adding a new chip
> easier, and then one patch at then end that adds the new chip. Hmm,
> it will probably be easier if I write those patches instead of
> reviewing them. I will followup with them. But note that I can
> only compile test them, so I would like to see tags for them.
> 
>> +
>> +static int pca9641_detect_id(struct i2c_client *client)
>> +{
>> +	int reg;
>> +
>> +	reg = pca9541_reg_read(client, PCA9641_ID);
>> +	if (reg == PCA9641_ID_MAGIC)
>> +		return 1;
>> +	else
>> +		return 0;
>> +}
> 
> This was not what I had in mind. If you do dig out the id, I think
> you should only use it to verify that the input to the probe function
> is correct and error out otherwise. But maybe I'm conservative?
> Anyway, with the above patches you will not need this.
> 
>> +/*
>>   * I2C init/probing/exit functions
>>   */
>>  static int pca9541_probe(struct i2c_client *client,
>> @@ -339,34 +492,45 @@ static int pca9541_probe(struct i2c_client *client,
>>  	struct pca9541 *data;
>>  	int force;
>>  	int ret;
>> +	int detect_id;
>>  
>>  	if (!i2c_check_functionality(adap, I2C_FUNC_SMBUS_BYTE_DATA))
>>  		return -ENODEV;
>>  
>> +	detect_id = pca9641_detect_id(client);
>>  	/*
>>  	 * I2C accesses are unprotected here.
>>  	 * We have to lock the adapter before releasing the bus.
>>  	 */
>> -	i2c_lock_adapter(adap);
>> -	pca9541_release_bus(client);
>> -	i2c_unlock_adapter(adap);
>> -
>> +	if (detect_id == 0) {
>> +		i2c_lock_adapter(adap);
>> +		pca9541_release_bus(client);
>> +		i2c_unlock_adapter(adap);
>> +	} else {
>> +		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, 1, sizeof(*data),
>> +	if (detect_id == 0) {
>> +		muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
>>  			     I2C_MUX_ARBITRATOR,
>>  			     pca9541_select_chan, pca9541_release_chan);
>> +	} else {
>> +		muxc = i2c_mux_alloc(adap, &client->dev, 1, sizeof(*data),
>> +			     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);
>> -
> 
> Please don't do spurious whitespace changes like this as part of a
> functional change.
> 
>>  	ret = i2c_mux_add_adapter(muxc, force, 0, 0);
>>  	if (ret)
>>  		return ret;
>>
> 
> You should change the Kconfig file to mention the new chip and you are
> still missing a devicetree binding.
> 
> Cheers,
> Peter
> 

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