Re: [PATCH v4 1/4] i2c: at91: Send bus clear command if SDA is down

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On 2/25/2020 4:50 PM, Codrin Ciubotariu wrote:
> After a transfer timeout, some faulty I2C slave devices might hold down
> the SDA pin. We can generate a bus clear command, hoping that the slave
> might release the pins.
> If the CLEAR command is not supported, we will use gpio recovery, if
> available, to reset the bus.
> 
> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@xxxxxxxxxxxxx>

Sounds good so
Acked-by: Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx>

Wolfram, you have accepted the v3 of the recovery support and requested 
these changes. It has been sent as a v4, but, in fact, this patch goes 
on top on v3. It could, should, have been a new patch.

Regards

Ludovic

> ---
> 
> Changes in v4:
>   - moved the HW bus clear command in a recover_bus() function, to be able
>     to just call i2c_recover_bus() if a transfer fails;
>   - recovery gpios are no longer taken if HW bus clear command is
>     supported;
> 
> Changes in v3:
>   - removed unnecessary condition from info print;
>   - removed unneded declarations;
> 
> Changes in v2:
>   - called i2c_recover_bus() after an error occurs, if SDA is down;
>   - release gpios if recovery information is incomplete;
> 
>   drivers/i2c/busses/i2c-at91-core.c   |  2 ++
>   drivers/i2c/busses/i2c-at91-master.c | 49 ++++++++++++++++++++++++----
>   drivers/i2c/busses/i2c-at91.h        |  7 +++-
>   3 files changed, 50 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91-core.c b/drivers/i2c/busses/i2c-at91-core.c
> index 3da1a8acecb5..e14edd236108 100644
> --- a/drivers/i2c/busses/i2c-at91-core.c
> +++ b/drivers/i2c/busses/i2c-at91-core.c
> @@ -131,6 +131,7 @@ 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 = {
> @@ -142,6 +143,7 @@ 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 0aba51a7df32..776e95962ab6 100644
> --- a/drivers/i2c/busses/i2c-at91-master.c
> +++ b/drivers/i2c/busses/i2c-at91-master.c
> @@ -480,7 +480,6 @@ 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;
>   
>   	/*
>   	 * WARNING: the TXCOMP bit in the Status Register is NOT a clear on
> @@ -641,11 +640,12 @@ 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
> +	 */
> +	i2c_recover_bus(&dev->adapter);
>   
>   	return ret;
>   }
> @@ -830,7 +830,7 @@ static void at91_unprepare_twi_recovery(struct i2c_adapter *adap)
>   	pinctrl_select_state(dev->pinctrl, dev->pinctrl_pins_default);
>   }
>   
> -static int at91_init_twi_recovery_info(struct platform_device *pdev,
> +static int at91_init_twi_recovery_gpio(struct platform_device *pdev,
>   				       struct at91_twi_dev *dev)
>   {
>   	struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
> @@ -880,6 +880,41 @@ static int at91_init_twi_recovery_info(struct platform_device *pdev,
>   	return 0;
>   }
>   
> +static int at91_twi_recover_bus_cmd(struct i2c_adapter *adap)
> +{
> +	struct at91_twi_dev *dev = i2c_get_adapdata(adap);
> +
> +	dev->transfer_status |= at91_twi_read(dev, AT91_TWI_SR);
> +	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);
> +	}
> +
> +	return 0;
> +}
> +
> +static int at91_init_twi_recovery_info(struct platform_device *pdev,
> +				       struct at91_twi_dev *dev)
> +{
> +	struct i2c_bus_recovery_info *rinfo = &dev->rinfo;
> +	bool has_clear_cmd = dev->pdata->has_clear_cmd;
> +
> +	if (!has_clear_cmd)
> +		return at91_init_twi_recovery_gpio(pdev, dev);
> +
> +	rinfo->recover_bus = at91_twi_recover_bus_cmd;
> +	dev->adapter.bus_recovery_info = rinfo;
> +
> +	return 0;
> +}
> +
>   int at91_twi_probe_master(struct platform_device *pdev,
>   			  u32 phy_addr, struct at91_twi_dev *dev)
>   {
> diff --git a/drivers/i2c/busses/i2c-at91.h b/drivers/i2c/busses/i2c-at91.h
> index f57a6cab96b4..7e7b4955ca7f 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;
>   };
>   
> 





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