From: Hubert Streidl <[email protected]>
By default the PMIC DA9063 2-wire interface is SMBus compliant. This
means the PMIC will automatically reset the interface when the clock
signal ceases for more than the SMBus timeout of 35 ms.
If the I2C driver / device is not capable of creating atomic I2C
transactions, a context change can cause a ceasing of the clock signal.
This can happen if for example a real-time thread is scheduled. Then
the DA9063 in SMBus mode will reset the 2-wire interface. Subsequently
a write message could end up in the wrong register. This could cause
unpredictable system behavior.
The DA9063 PMIC also supports an I2C compliant mode for the 2-wire
interface. This mode does not reset the interface when the clock
signal ceases. Thus the problem depicted above does not occur.
This patch tests for the bus functionality "I2C_FUNC_I2C". It can
reasonably be assumed that the bus cannot obey SMBus timings if
this functionality is set. SMBus commands most probably are emulated
in this case which is prone to the latency issue described above.
This patch enables the I2C bus mode if I2C_FUNC_I2C is set or
otherwise keeps the default SMBus mode.
Signed-off-by: Hubert Streidl <[email protected]>
Signed-off-by: Mark Jonas <[email protected]>
---
drivers/mfd/da9063-i2c.c | 10 ++++++++++
include/linux/mfd/da9063/registers.h | 3 +++
2 files changed, 13 insertions(+)
diff --git a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c
index 3781d0bb7786..e8a022e697c5 100644
--- a/drivers/mfd/da9063-i2c.c
+++ b/drivers/mfd/da9063-i2c.c
@@ -442,6 +442,16 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
return ret;
}
+ /* If SMBus is not available and only I2C is possible, enter I2C mode */
+ if (i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C)) {
+ ret = regmap_clear_bits(da9063->regmap, DA9063_REG_CONFIG_J,
+ DA9063_TWOWIRE_TO);
+ if (ret < 0) {
+ dev_err(da9063->dev, "Failed to set Two-Wire Bus Mode.\n");
+ return -EIO;
+ }
+ }
+
return da9063_device_init(da9063, i2c->irq);
}
diff --git a/include/linux/mfd/da9063/registers.h b/include/linux/mfd/da9063/registers.h
index 1dbabf1b3cb8..6e0f66a2e727 100644
--- a/include/linux/mfd/da9063/registers.h
+++ b/include/linux/mfd/da9063/registers.h
@@ -1037,6 +1037,9 @@
#define DA9063_NONKEY_PIN_AUTODOWN 0x02
#define DA9063_NONKEY_PIN_AUTOFLPRT 0x03
+/* DA9063_REG_CONFIG_J (addr=0x10F) */
+#define DA9063_TWOWIRE_TO 0x40
+
/* DA9063_REG_MON_REG_5 (addr=0x116) */
#define DA9063_MON_A8_IDX_MASK 0x07
#define DA9063_MON_A8_IDX_NONE 0x00
--
2.25.1
On Mon, Mar 15, 2021 at 05:09:03PM +0100, Mark Jonas wrote:
> From: Hubert Streidl <[email protected]>
>
> By default the PMIC DA9063 2-wire interface is SMBus compliant. This
> means the PMIC will automatically reset the interface when the clock
> signal ceases for more than the SMBus timeout of 35 ms.
>
> If the I2C driver / device is not capable of creating atomic I2C
> transactions, a context change can cause a ceasing of the clock signal.
> This can happen if for example a real-time thread is scheduled. Then
> the DA9063 in SMBus mode will reset the 2-wire interface. Subsequently
> a write message could end up in the wrong register. This could cause
> unpredictable system behavior.
>
> The DA9063 PMIC also supports an I2C compliant mode for the 2-wire
> interface. This mode does not reset the interface when the clock
> signal ceases. Thus the problem depicted above does not occur.
>
> This patch tests for the bus functionality "I2C_FUNC_I2C". It can
> reasonably be assumed that the bus cannot obey SMBus timings if
> this functionality is set. SMBus commands most probably are emulated
> in this case which is prone to the latency issue described above.
>
> This patch enables the I2C bus mode if I2C_FUNC_I2C is set or
> otherwise keeps the default SMBus mode.
>
> Signed-off-by: Hubert Streidl <[email protected]>
> Signed-off-by: Mark Jonas <[email protected]>
From an I2C point of view, this is the correct approach:
Reviewed-by: Wolfram Sang <[email protected]>
On Mon, 15 Mar 2021, Mark Jonas wrote:
> From: Hubert Streidl <[email protected]>
>
> By default the PMIC DA9063 2-wire interface is SMBus compliant. This
> means the PMIC will automatically reset the interface when the clock
> signal ceases for more than the SMBus timeout of 35 ms.
>
> If the I2C driver / device is not capable of creating atomic I2C
> transactions, a context change can cause a ceasing of the clock signal.
> This can happen if for example a real-time thread is scheduled. Then
> the DA9063 in SMBus mode will reset the 2-wire interface. Subsequently
> a write message could end up in the wrong register. This could cause
> unpredictable system behavior.
>
> The DA9063 PMIC also supports an I2C compliant mode for the 2-wire
> interface. This mode does not reset the interface when the clock
> signal ceases. Thus the problem depicted above does not occur.
>
> This patch tests for the bus functionality "I2C_FUNC_I2C". It can
> reasonably be assumed that the bus cannot obey SMBus timings if
> this functionality is set. SMBus commands most probably are emulated
> in this case which is prone to the latency issue described above.
>
> This patch enables the I2C bus mode if I2C_FUNC_I2C is set or
> otherwise keeps the default SMBus mode.
>
> Signed-off-by: Hubert Streidl <[email protected]>
> Signed-off-by: Mark Jonas <[email protected]>
> ---
> drivers/mfd/da9063-i2c.c | 10 ++++++++++
> include/linux/mfd/da9063/registers.h | 3 +++
> 2 files changed, 13 insertions(+)
Code looks good to me now, thanks.
However, this doesn't look like it would pass checkpatch.
Have you tried to build with W=1 and checkpatch?
> diff --git a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c
> index 3781d0bb7786..e8a022e697c5 100644
> --- a/drivers/mfd/da9063-i2c.c
> +++ b/drivers/mfd/da9063-i2c.c
> @@ -442,6 +442,16 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
> return ret;
> }
>
> + /* If SMBus is not available and only I2C is possible, enter I2C mode */
> + if (i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C)) {
> + ret = regmap_clear_bits(da9063->regmap, DA9063_REG_CONFIG_J,
> + DA9063_TWOWIRE_TO);
> + if (ret < 0) {
> + dev_err(da9063->dev, "Failed to set Two-Wire Bus Mode.\n");
> + return -EIO;
> + }
> + }
> +
> return da9063_device_init(da9063, i2c->irq);
> }
>
> diff --git a/include/linux/mfd/da9063/registers.h b/include/linux/mfd/da9063/registers.h
> index 1dbabf1b3cb8..6e0f66a2e727 100644
> --- a/include/linux/mfd/da9063/registers.h
> +++ b/include/linux/mfd/da9063/registers.h
> @@ -1037,6 +1037,9 @@
> #define DA9063_NONKEY_PIN_AUTODOWN 0x02
> #define DA9063_NONKEY_PIN_AUTOFLPRT 0x03
>
> +/* DA9063_REG_CONFIG_J (addr=0x10F) */
> +#define DA9063_TWOWIRE_TO 0x40
> +
> /* DA9063_REG_MON_REG_5 (addr=0x116) */
> #define DA9063_MON_A8_IDX_MASK 0x07
> #define DA9063_MON_A8_IDX_NONE 0x00
--
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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