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

From: Ludovic Desroches
Date: Thu Jan 09 2020 - 02:48:03 EST

On Fri, Jan 03, 2020 at 09:49:07AM +0000, Codrin Ciubotariu - M19940 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@xxxxxxxxxxxxx>

This patch may conflict with another one removing the explicit set to
false.

> ---
>
> Changes in v2:
> - use CLEAR command only if SDA is down; update patch subject to
> reflect this;
> - 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 */

In this case it's probably worth keeping it.

Ludovic

> };
>
> 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