Re: [PATCH v2 3/6] i2c: at91: Send bus clear command if SCL is down

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Fri, Jan 03, 2020 at 09:49:07AM +0000, Codrin.Ciubotariu@microchip.com wrote:
> After a transfer timeout, some faulty I2C slave devices might hold down
> the SCL pin. We can generate a bus clear command, hoping that the slave
> might release the pins.
> 
> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
> ---
> 
> Changes in v2:
>  - use CLEAR command only if SDA is down; update patch subject to
>    reflect this;

Given this change, shouldn't the commit message above be updated?

>  - CLEAR command is no longer used for sama5d2, only sam9x60;
> 
>  drivers/i2c/busses/i2c-at91-core.c   |  9 ++++++++
>  drivers/i2c/busses/i2c-at91-master.c | 32 +++++++++++++++++++++++-----
>  drivers/i2c/busses/i2c-at91.h        |  7 +++++-
>  3 files changed, 42 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91-core.c b/drivers/i2c/busses/i2c-at91-core.c
> index e13af4874976..128eafc05adb 100644
> --- a/drivers/i2c/busses/i2c-at91-core.c
> +++ b/drivers/i2c/busses/i2c-at91-core.c
> @@ -71,6 +71,7 @@ static struct at91_twi_pdata at91rm9200_config = {
>  	.has_dig_filtr = false,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static struct at91_twi_pdata at91sam9261_config = {
> @@ -82,6 +83,7 @@ static struct at91_twi_pdata at91sam9261_config = {
>  	.has_dig_filtr = false,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static struct at91_twi_pdata at91sam9260_config = {
> @@ -93,6 +95,7 @@ static struct at91_twi_pdata at91sam9260_config = {
>  	.has_dig_filtr = false,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static struct at91_twi_pdata at91sam9g20_config = {
> @@ -104,6 +107,7 @@ static struct at91_twi_pdata at91sam9g20_config = {
>  	.has_dig_filtr = false,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static struct at91_twi_pdata at91sam9g10_config = {
> @@ -115,6 +119,7 @@ static struct at91_twi_pdata at91sam9g10_config = {
>  	.has_dig_filtr = false,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static const struct platform_device_id at91_twi_devtypes[] = {
> @@ -148,6 +153,7 @@ static struct at91_twi_pdata at91sam9x5_config = {
>  	.has_dig_filtr = false,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static struct at91_twi_pdata sama5d4_config = {
> @@ -159,6 +165,7 @@ static struct at91_twi_pdata sama5d4_config = {
>  	.has_dig_filtr = true,
>  	.has_adv_dig_filtr = false,
>  	.has_ana_filtr = false,
> +	.has_clear_cmd = false,
>  };
>  
>  static struct at91_twi_pdata sama5d2_config = {
> @@ -170,6 +177,7 @@ static struct at91_twi_pdata sama5d2_config = {
>  	.has_dig_filtr = true,
>  	.has_adv_dig_filtr = true,
>  	.has_ana_filtr = true,
> +	.has_clear_cmd = false,	/* due to errata, CLEAR cmd is not working */
>  };
>  
>  static struct at91_twi_pdata sam9x60_config = {
> @@ -181,6 +189,7 @@ static struct at91_twi_pdata sam9x60_config = {
>  	.has_dig_filtr = true,
>  	.has_adv_dig_filtr = true,
>  	.has_ana_filtr = true,
> +	.has_clear_cmd = true,
>  };
>  
>  static const struct of_device_id atmel_twi_dt_ids[] = {
> diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
> index c55e8ff35201..8c4f20317847 100644
> --- a/drivers/i2c/busses/i2c-at91-master.c
> +++ b/drivers/i2c/busses/i2c-at91-master.c
> @@ -480,7 +480,7 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
>  	unsigned long time_left;
>  	bool has_unre_flag = dev->pdata->has_unre_flag;
>  	bool has_alt_cmd = dev->pdata->has_alt_cmd;
> -	struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
> +	bool has_clear_cmd = dev->pdata->has_clear_cmd;
>  
>  	/*
>  	 * WARNING: the TXCOMP bit in the Status Register is NOT a clear on
> @@ -641,10 +641,32 @@ static int at91_do_twi_transfer(struct at91_twi_dev *dev)
>  			       AT91_TWI_THRCLR | AT91_TWI_LOCKCLR);
>  	}
>  
> -	if (rinfo->get_sda && !(rinfo->get_sda(&dev->adapter))) {
> -		dev_dbg(dev->dev,
> -			"SDA is down; clear bus using gpio\n");
> -		i2c_recover_bus(&dev->adapter);
> +	/*
> +	 * some faulty I2C slave devices might hold SDA down;
> +	 * we can send a bus clear command, hoping that the pins will be
> +	 * released
> +	 */
> +	if (has_clear_cmd) {
> +		if (!(dev->transfer_status & AT91_TWI_SDA)) {
> +			dev_dbg(dev->dev,
> +				"SDA is down; sending bus clear command\n");
> +			if (dev->use_alt_cmd) {
> +				unsigned int acr;
> +
> +				acr = at91_twi_read(dev, AT91_TWI_ACR);
> +				acr &= ~AT91_TWI_ACR_DATAL_MASK;
> +				at91_twi_write(dev, AT91_TWI_ACR, acr);
> +			}
> +			at91_twi_write(dev, AT91_TWI_CR, AT91_TWI_CLEAR);
> +		}
> +	} else {
> +		struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
> +
> +		if (rinfo->get_sda && !(rinfo->get_sda(&dev->adapter))) {
> +			dev_dbg(dev->dev,
> +				"SDA is down; clear bus using gpio\n");
> +			i2c_recover_bus(&dev->adapter);
> +		}
>  	}
>  
>  	return ret;
> diff --git a/drivers/i2c/busses/i2c-at91.h b/drivers/i2c/busses/i2c-at91.h
> index eb335b71e775..80f77d523346 100644
> --- a/drivers/i2c/busses/i2c-at91.h
> +++ b/drivers/i2c/busses/i2c-at91.h
> @@ -36,6 +36,7 @@
>  #define	AT91_TWI_SVDIS		BIT(5)	/* Slave Transfer Disable */
>  #define	AT91_TWI_QUICK		BIT(6)	/* SMBus quick command */
>  #define	AT91_TWI_SWRST		BIT(7)	/* Software Reset */
> +#define	AT91_TWI_CLEAR		BIT(15) /* Bus clear command */
>  #define	AT91_TWI_ACMEN		BIT(16) /* Alternative Command Mode Enable */
>  #define	AT91_TWI_ACMDIS		BIT(17) /* Alternative Command Mode Disable */
>  #define	AT91_TWI_THRCLR		BIT(24) /* Transmit Holding Register Clear */
> @@ -69,6 +70,8 @@
>  #define	AT91_TWI_NACK		BIT(8)	/* Not Acknowledged */
>  #define	AT91_TWI_EOSACC		BIT(11)	/* End Of Slave Access */
>  #define	AT91_TWI_LOCK		BIT(23) /* TWI Lock due to Frame Errors */
> +#define	AT91_TWI_SCL		BIT(24) /* TWI SCL status */
> +#define	AT91_TWI_SDA		BIT(25) /* TWI SDA status */
>  
>  #define	AT91_TWI_INT_MASK \
>  	(AT91_TWI_TXCOMP | AT91_TWI_RXRDY | AT91_TWI_TXRDY | AT91_TWI_NACK \
> @@ -81,7 +84,8 @@
>  #define	AT91_TWI_THR		0x0034	/* Transmit Holding Register */
>  
>  #define	AT91_TWI_ACR		0x0040	/* Alternative Command Register */
> -#define	AT91_TWI_ACR_DATAL(len)	((len) & 0xff)
> +#define	AT91_TWI_ACR_DATAL_MASK	GENMASK(15, 0)
> +#define	AT91_TWI_ACR_DATAL(len)	((len) & AT91_TWI_ACR_DATAL_MASK)
>  #define	AT91_TWI_ACR_DIR	BIT(8)
>  
>  #define AT91_TWI_FILTR		0x0044
> @@ -118,6 +122,7 @@ struct at91_twi_pdata {
>  	bool has_dig_filtr;
>  	bool has_adv_dig_filtr;
>  	bool has_ana_filtr;
> +	bool has_clear_cmd;
>  	struct at_dma_slave dma_slave;
>  };
>  
> -- 
> 2.20.1
> 
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