lkml.org 
[lkml]   [2021]   [Mar]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4] mfd: da9063: Support SMBus and I2C mode
On Mon, 08 Feb 2021, Mark Jonas wrote:

> From: Hubert Streidl <hubert.streidl@de.bosch.com>
>
> 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 enables the SMBus mode for a native SMBus controller
> which doesn't have I2C_FUNC_I2C set.
>
> Signed-off-by: Hubert Streidl <hubert.streidl@de.bosch.com>
> Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>
> ---
> Changes in v4:
> - Remove logging of selected 2-wire bus mode.
>
> Changes in v3:
> - busmode now contains the correct bit DA9063_TWOWIRE_TO
>
> Changes in v2:
> - Implement proposal by Adam Thomson and Wolfram Sang to check for
> functionality I2C_FUNC_I2C instead of introducing a new DT property.
>
> drivers/mfd/da9063-i2c.c | 11 +++++++++++
> include/linux/mfd/da9063/registers.h | 3 +++
> 2 files changed, 14 insertions(+)
>
> diff --git a/drivers/mfd/da9063-i2c.c b/drivers/mfd/da9063-i2c.c
> index 3781d0bb7786..9450c95a3741 100644
> --- a/drivers/mfd/da9063-i2c.c
> +++ b/drivers/mfd/da9063-i2c.c
> @@ -355,6 +355,7 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
> const struct i2c_device_id *id)
> {
> struct da9063 *da9063;
> + unsigned int busmode;
> int ret;
>
> da9063 = devm_kzalloc(&i2c->dev, sizeof(struct da9063), GFP_KERNEL);
> @@ -442,6 +443,16 @@ static int da9063_i2c_probe(struct i2c_client *i2c,
> return ret;
> }
>
> + busmode = i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C) ?
> + 0 : DA9063_TWOWIRE_TO;

Nit: I find ternaries like this tend to complicate matters and
harm readability rather than the converse.

> + ret = regmap_update_bits(da9063->regmap, DA9063_REG_CONFIG_J,
> + DA9063_TWOWIRE_TO, busmode);
> + if (ret < 0) {
> + dev_err(da9063->dev, "Failed to set 2-wire bus mode.\n");
> + return -EIO;
> + }

I'm a little confused by this. It's likely just me, but I would still
like some clarification.

So you write to the TWOWIRE register despite whether I2C is operable
not, which I guess is fine.

But what if I2C is disabled and the update fails. You seem to complain
to the user that a failure occurred and return an error even if the
configuration is invalid in the first place.

Would it not be better to encapsulate the update inside the
functionality check?

> 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
Follow Linaro: Facebook | Twitter | Blog

\
 
 \ /
  Last update: 2021-03-08 15:43    [W:0.116 / U:1.284 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site