From: Lee Jones <lee.jones@linaro.org>
To: Mark Jonas <mark.jonas@de.bosch.com>
Cc: Support Opensource <support.opensource@diasemi.com>,
linux-kernel@vger.kernel.org, linux-i2c@vger.kernel.org,
Adam.Thomson.Opensource@diasemi.com,
stwiss.opensource@diasemi.com, marek.vasut@gmail.com,
tingquan.ruan@cn.bosch.com, hubert.streidl@de.bosch.com,
Wolfram Sang <wsa@kernel.org>
Subject: Re: [PATCH v4] mfd: da9063: Support SMBus and I2C mode
Date: Mon, 8 Mar 2021 14:42:11 +0000 [thread overview]
Message-ID: <20210308144211.GK4931@dell> (raw)
In-Reply-To: <20210208152758.13093-1-mark.jonas@de.bosch.com>
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
next prev parent reply other threads:[~2021-03-08 14:43 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 15:27 [PATCH v4] mfd: da9063: Support SMBus and I2C mode Mark Jonas
2021-02-09 10:40 ` Wolfram Sang
2021-02-09 13:18 ` Adam Thomson
2021-02-19 16:39 ` AW: " Jonas Mark (BT-FIR/ENG1-Grb)
2021-02-20 11:07 ` Wolfram Sang
2021-02-22 9:10 ` Lee Jones
2021-03-08 14:42 ` Lee Jones [this message]
2021-03-09 8:19 ` Mark Jonas
2021-03-09 9:42 ` Lee Jones
2021-03-09 22:42 ` Adam Ward
2021-03-10 8:58 ` Lee Jones
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210308144211.GK4931@dell \
--to=lee.jones@linaro.org \
--cc=Adam.Thomson.Opensource@diasemi.com \
--cc=hubert.streidl@de.bosch.com \
--cc=linux-i2c@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=marek.vasut@gmail.com \
--cc=mark.jonas@de.bosch.com \
--cc=stwiss.opensource@diasemi.com \
--cc=support.opensource@diasemi.com \
--cc=tingquan.ruan@cn.bosch.com \
--cc=wsa@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).