Re: [PATCH v2 1/1] i2c: algo-pca: Reapply i2c bus settings after reset

[Andy Shevchenko]

On Wed, Sep 02, 2020 at 09:17:47AM +1200, Evan Nimmo wrote:
> If something goes wrong (such as the SCL being stuck low) then we need
> to reset the PCA chip. The issue with this is that on reset we lose all
> config settings and the chip ends up in a disabled state which results
> in a lock up/high cpu usage. We need to re-apply any configuration that

cpu -> CPU (I guess Wolfram can decide with this when applying)

> had previously been set and re-enable the chip.

FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

> Signed-off-by: Evan Nimmo <evan.nimmo@xxxxxxxxxxxxxxxxxxx>
> ---
> changes in v2:
> - changed lowercase "pca to uppercase "PCA".
> - reworded and reformatted the multiline comment.
> - moved the clock frequency KERN_INFO closer to the call that sets this.
> - moved the i2c_bus_settings struct to the more generic i2c.h and removed
> - the comments indicating this as being for the pca chip.
> 
>  drivers/i2c/algos/i2c-algo-pca.c | 36 +++++++++++++++++++++-----------
>  include/linux/i2c-algo-pca.h     |  1 +
>  include/linux/i2c.h              | 14 +++++++++++++
>  3 files changed, 39 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/i2c/algos/i2c-algo-pca.c b/drivers/i2c/algos/i2c-algo-pca.c
> index 710fbef9a9c2..8b98b737b499 100644
> --- a/drivers/i2c/algos/i2c-algo-pca.c
> +++ b/drivers/i2c/algos/i2c-algo-pca.c
> @@ -41,8 +41,22 @@ static void pca_reset(struct i2c_algo_pca_data *adap)
>  		pca_outw(adap, I2C_PCA_INDPTR, I2C_PCA_IPRESET);
>  		pca_outw(adap, I2C_PCA_IND, 0xA5);
>  		pca_outw(adap, I2C_PCA_IND, 0x5A);
> +
> +		/*
> +		 * After a reset we need to re-apply any configuration
> +		 * (calculated in pca_init) to get the bus in a working state.
> +		 */
> +		pca_outw(adap, I2C_PCA_INDPTR, I2C_PCA_IMODE);
> +		pca_outw(adap, I2C_PCA_IND, adap->bus_settings.mode);
> +		pca_outw(adap, I2C_PCA_INDPTR, I2C_PCA_ISCLL);
> +		pca_outw(adap, I2C_PCA_IND, adap->bus_settings.tlow);
> +		pca_outw(adap, I2C_PCA_INDPTR, I2C_PCA_ISCLH);
> +		pca_outw(adap, I2C_PCA_IND, adap->bus_settings.thi);
> +
> +		pca_set_con(adap, I2C_PCA_CON_ENSIO);
>  	} else {
>  		adap->reset_chip(adap->data);
> +		pca_set_con(adap, I2C_PCA_CON_ENSIO | adap->bus_settings.clock_freq);
>  	}
>  }
>  
> @@ -423,13 +437,15 @@ static int pca_init(struct i2c_adapter *adap)
>  				" Use the nominal frequency.\n", adap->name);
>  		}
>  
> -		pca_reset(pca_data);
> -
>  		clock = pca_clock(pca_data);
> +
>  		printk(KERN_INFO "%s: Clock frequency is %dkHz\n",
>  		     adap->name, freqs[clock]);
>  
> -		pca_set_con(pca_data, I2C_PCA_CON_ENSIO | clock);
> +		/* Store settings as these will be needed when the PCA chip is reset */
> +		pca_data->bus_settings.clock_freq = clock;
> +
> +		pca_reset(pca_data);
>  	} else {
>  		int clock;
>  		int mode;
> @@ -496,19 +512,15 @@ static int pca_init(struct i2c_adapter *adap)
>  			thi = tlow * min_thi / min_tlow;
>  		}
>  
> +		/* Store settings as these will be needed when the PCA chip is reset */
> +		pca_data->bus_settings.mode = mode;
> +		pca_data->bus_settings.tlow = tlow;
> +		pca_data->bus_settings.thi = thi;
> +
>  		pca_reset(pca_data);
>  
>  		printk(KERN_INFO
>  		     "%s: Clock frequency is %dHz\n", adap->name, clock * 100);
> -
> -		pca_outw(pca_data, I2C_PCA_INDPTR, I2C_PCA_IMODE);
> -		pca_outw(pca_data, I2C_PCA_IND, mode);
> -		pca_outw(pca_data, I2C_PCA_INDPTR, I2C_PCA_ISCLL);
> -		pca_outw(pca_data, I2C_PCA_IND, tlow);
> -		pca_outw(pca_data, I2C_PCA_INDPTR, I2C_PCA_ISCLH);
> -		pca_outw(pca_data, I2C_PCA_IND, thi);
> -
> -		pca_set_con(pca_data, I2C_PCA_CON_ENSIO);
>  	}
>  	udelay(500); /* 500 us for oscillator to stabilise */
>  
> diff --git a/include/linux/i2c-algo-pca.h b/include/linux/i2c-algo-pca.h
> index d03071732db4..97d1f4cd8e56 100644
> --- a/include/linux/i2c-algo-pca.h
> +++ b/include/linux/i2c-algo-pca.h
> @@ -64,6 +64,7 @@ struct i2c_algo_pca_data {
>  	 * For PCA9665, use the frequency you want here. */
>  	unsigned int			i2c_clock;
>  	unsigned int			chip;
> +	struct i2c_bus_settings		bus_settings;
>  };
>  
>  int i2c_pca_add_bus(struct i2c_adapter *);
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index fc55ea41d323..8c5138fbe532 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -724,6 +724,20 @@ struct i2c_adapter {
>  };
>  #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
>  
> +/**
> + * struct i2c_bus_settings - The configured i2c bus settings
> + * @mode: Configured i2c bus mode
> + * @tlow: Configured SCL LOW period
> + * @thi: Configured SCL HIGH period
> + * @clock_freq: The configured clock frequency
> + */
> +struct i2c_bus_settings {
> +	int mode;
> +	int tlow;
> +	int thi;
> +	int clock_freq;
> +};
> +
>  static inline void *i2c_get_adapdata(const struct i2c_adapter *adap)
>  {
>  	return dev_get_drvdata(&adap->dev);
> -- 
> 2.27.0
> 

-- 
With Best Regards,
Andy Shevchenko