linux-kernel - Re: [PATCH] i2c: algo-pca: Reapply i2c bus settings after reset

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Date:   Tue, 1 Sep 2020 20:58:41 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Evan Nimmo <Evan.Nimmo@...iedtelesis.co.nz>,
        "wsa@...nel.org" <wsa@...nel.org>,
        "andriy.shevchenko@...ux.intel.com" 
        <andriy.shevchenko@...ux.intel.com>,
        "jdelvare@...e.de" <jdelvare@...e.de>,
        "jarkko.nikula@...ux.intel.com" <jarkko.nikula@...ux.intel.com>
CC:     "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] i2c: algo-pca: Reapply i2c bus settings after reset

Hi Evan,

One minor comment from me below. With that

Reviewed-by: Chris Packham <chris.packham@...iedtelesis.co.nz>

On 1/09/20 12:57 pm, 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
> had previously been set and re-enable the chip.
>
> Signed-off-by: Evan Nimmo <evan.nimmo@...iedtelesis.co.nz>
> ---
>   drivers/i2c/algos/i2c-algo-pca.c | 36 +++++++++++++++++++++-----------
>   include/linux/i2c-algo-pca.h     | 15 +++++++++++++
>   2 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..2e4e27073f40 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);
> +
> +		/* We need to apply any configuration settings that
> +		 * were calculated in the pca_init function. The reset
> +		 * results in these changes being set back to defaults.
> +		 */

"these changes" doesn't read well. How about

/*
  * 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);
>   		}
>   
> +		clock = pca_clock(pca_data);
> +
> +		/* Store settings as these will be needed when the pca chip is reset */
> +		pca_data->bus_settings.clock_freq = clock;
> +
>   		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);
>   	} 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..ebeadb80c797 100644
> --- a/include/linux/i2c-algo-pca.h
> +++ b/include/linux/i2c-algo-pca.h
> @@ -53,6 +53,20 @@
>   #define I2C_PCA_CON_SI		0x08 /* Serial Interrupt */
>   #define I2C_PCA_CON_CR		0x07 /* Clock Rate (MASK) */
>   
> +/**
> + * struct i2c_bus_settings - The configured i2c bus settings
> + * @mode: Configured i2c bus mode (PCA9665)
> + * @tlow: Configured SCL LOW period (PCA9665)
> + * @thi: Configured SCL HIGH period (PCA9665)
> + * @clock_freq: The configured clock frequency (PCA9564)
> + */
> +struct i2c_bus_settings {
> +	int mode;
> +	int tlow;
> +	int thi;
> +	int clock_freq;
> +};
> +
>   struct i2c_algo_pca_data {
>   	void 				*data;	/* private low level data */
>   	void (*write_byte)		(void *data, int reg, int val);
> @@ -64,6 +78,7 @@ 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 *);