Date:   Wed, 24 Aug 2022 03:50:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Duke Du <dukedu83@...il.com>
Cc:     jdelvare@...e.com, corbet@....net, linux-hwmon@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        fran.hsu@...ntatw.com, charles.hsu@...ntatw.com,
        george.hung@...ntatw.com, duke.du@...ntatw.com
Subject: Re: [PATCH v3] hwmon: Add driver for the TEXAS TPS546D24 Buck
 Converter.

On Wed, Aug 24, 2022 at 01:58:33PM +0800, Duke Du wrote:
> Hi Guenter,
> Thanks for your reply !
> But I have some confusion as following, please help to give me some feedback.
> Thanks a lot !
> 
> On Fri, Aug 19, 2022 at 9:35 PM Guenter Roeck <linux@...ck-us.net> wrote:
> >
> > On Fri, Aug 19, 2022 at 11:04:43AM +0800, Duke Du wrote:
> > > Add the pmbus driver for TEXAS tps546d24 Buck Converter. The
> > > tps546d24 PMBUS_VOUT_MODE is 0x97 (i.e. the bit 5~7 are 100)
> > > which could not meet the standard pmbus spec, the standard mode
> > > of PMBUS_VOUT_MODE must be 000 (linear foramt) or 001 (vid format).
> > > Make the tps546d24 PMBUS_VOUT_MODE return value 0x17 (i.e. the
> > > bit5~7 are 000), VOUT returned value is linear11.
> > >
> >
> > First of all, the above should be documented as comment in the
> > implementation.
> >
> > Second, this is actually problematic. In PMBus version 1.3.1, bit
> > 7 of PMBUS_VOUT_MODE no longer describes the mode (linear, vid, direct,
> > IEEE) but Absolute vs/ Relative VOUT voltages. This affects vout fault
> > and warning limits. If the relative mode bit is set, those limits
> > are supposed to reflect percentages, not absolute voltages.
> >
> > This means that the driver interprets vout voltage limits wrongly,
> > at least if the chip works as described in the datasheet. Changing
> > the reported value of PMBUS_VOUT_MODE is actually counter-productive.
> >
> > This means we'll need a number of changes. At the very least, the
> > PMBus core needs to be be modified to only use bit 5 and 6 to determine
> > the mode. On top of that, the driver probe function should update
> > VOUT_MODE and clear bit 7. It might also make sense to warn in the
> > PMBus core if mode bit 7 is set.
> >
> 
> When the vout mode bit 7 is set, we update vout mode and clear bit 7
> in the driver probe function, this operation is the same as changing
> the reported value of PMBUS_VOUT_MODE ?

Absolutely not. When changing the bit in the register, the chip operation
mode changes, and the associated values (VOUT*) change from relative
to absolute mode. When changing the value reported by the chip, nothing
changes from the chip side, it still operates in relative mode, and all
VOUT* registers are set to relative mode.

Guenter

> Maybe I misunderstood, could you please help to explain clearly about this ?
> Thanks again for your help :)
> 
> Thanks,
> Duke
> 
> > An alternative to the second change would be to implement relative
> > vout support in the PMBus core, but that would be much more complex.
> > We could also clear the relative bit in the PMBus core, but that might
> > lead to unexpected side effects (we don't know how various chips
> > respond to that) and thus probably not be a good idea.
> >
> > > Signed-off-by: Duke Du <Duke.Du@...ntatw.com>
> >
> > This e-mail address does not match the e-mail address used to send
> > the patch, resulting in a checkpatch warning. Please fix.
> >
> > More comments inline.
> >
> > Thanks,
> > Guenter
> >
> > > ---
> > > Change in v1:
> > >     Initial patchset.
> > > Change in v2:
> > >     Correct the tps546d24.rst format.
> > > Change in v3:
> > >     1. Modify the patch description.
> > >     2. Put the change log between the dashes and diffstat.
> > > ---
> > > ---
> > >  Documentation/hwmon/index.rst     |  1 +
> > >  Documentation/hwmon/tps546d24.rst | 35 +++++++++++++++++++
> > >  MAINTAINERS                       |  7 ++++
> > >  drivers/hwmon/pmbus/Kconfig       |  9 +++++
> > >  drivers/hwmon/pmbus/Makefile      |  1 +
> > >  drivers/hwmon/pmbus/tps546d24.c   | 73 +++++++++++++++++++++++++++++++++++++++
> > >  6 files changed, 126 insertions(+)
> > >  create mode 100644 Documentation/hwmon/tps546d24.rst
> > >  create mode 100644 drivers/hwmon/pmbus/tps546d24.c
> > >
> > > diff --git a/Documentation/hwmon/index.rst b/Documentation/hwmon/index.rst
> > > index f7113b0..d3eede4 100644
> > > --- a/Documentation/hwmon/index.rst
> > > +++ b/Documentation/hwmon/index.rst
> > > @@ -205,6 +205,7 @@ Hardware Monitoring Kernel Drivers
> > >     tps23861
> > >     tps40422
> > >     tps53679
> > > +   tps546d24
> > >     twl4030-madc-hwmon
> > >     ucd9000
> > >     ucd9200
> > > diff --git a/Documentation/hwmon/tps546d24.rst b/Documentation/hwmon/tps546d24.rst
> > > new file mode 100644
> > > index 0000000..3061fd8
> > > --- /dev/null
> > > +++ b/Documentation/hwmon/tps546d24.rst
> > > @@ -0,0 +1,35 @@
> > > +.. SPDX-License-Identifier: GPL-2.0-only
> > > +
> > > +Kernel driver tps546d24
> > > +======================
> > > +
> > > +Supported chips:
> > > +
> > > +  * TI TPS546D24
> > > +
> > > +    Prefix: 'tps546d24'
> > > +
> > > +    Addresses scanned: -
> > > +
> > > +    Datasheet: https://www.ti.com/lit/gpn/tps546d24
> > > +
> > > +Author: Duke Du <dukedu83@...il.com>
> >
> > This needs to match Author and Signed-off-by:. This applies to all
> > e-mail addresses.
> >
> > > +
> > > +
> > > +Description
> > > +-----------
> > > +
> > > +The TPS546D24A is a highly integrated, non-isolated DC/DC converter capable
> > > +of high frequency operation and 40-A current output from a 7-mm x 5-mm
> > > +package.
> > > +
> > > +Two, three, and four TPS546D24A devices can be interconnected
> > > +to provide up to 160 A on a single output. The device has an option to
> > > +overdrive the internal 5-V LDO with an external 5-V supply via the VDD5
> > > +pin to improve efficiency and reduce power dissipation of the converter.
> > > +
> > > +
> > > +Platform data support
> > > +---------------------
> > > +
> > > +The driver supports standard PMBus driver platform data.
> > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > index 8a5012b..fa2d4fb 100644
> > > --- a/MAINTAINERS
> > > +++ b/MAINTAINERS
> > > @@ -20583,6 +20583,13 @@ Q:   https://patchwork.kernel.org/project/linux-integrity/list/
> > >  T:   git git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git
> > >  F:   drivers/char/tpm/
> > >
> > > +TPS546D24 DRIVER
> > > +M:   Duke Du <dukedu83@...il.com>
> > > +L:   linux-hwmon@...r.kernel.org
> > > +S:   Maintained
> > > +F:   Documentation/hwmon/tps546d24.rst
> > > +F:   drivers/hwmon/pmbus/tps546d24.c
> > > +
> > >  TRACING
> > >  M:   Steven Rostedt <rostedt@...dmis.org>
> > >  M:   Ingo Molnar <mingo@...hat.com>
> > > diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
> > > index 951e4a9..89668af 100644
> > > --- a/drivers/hwmon/pmbus/Kconfig
> > > +++ b/drivers/hwmon/pmbus/Kconfig
> > > @@ -397,6 +397,15 @@ config SENSORS_TPS53679
> > >         This driver can also be built as a module. If so, the module will
> > >         be called tps53679.
> > >
> > > +config SENSORS_TPS546D24
> > > +     tristate "TPS546D24"
> > > +     help
> > > +       If you say yes here you get hardware monitoring support for TEXAS
> > > +       TPS546D24.
> > > +
> > > +       This driver can also be built as a module. If so, the module will
> > > +       be called tps546d24
> > > +
> > >  config SENSORS_UCD9000
> > >       tristate "TI UCD90120, UCD90124, UCD90160, UCD90320, UCD9090, UCD90910"
> > >       help
> > > diff --git a/drivers/hwmon/pmbus/Makefile b/drivers/hwmon/pmbus/Makefile
> > > index e2fe86f..0002dbe 100644
> > > --- a/drivers/hwmon/pmbus/Makefile
> > > +++ b/drivers/hwmon/pmbus/Makefile
> > > @@ -41,6 +41,7 @@ obj-$(CONFIG_SENSORS_Q54SJ108A2)    += q54sj108a2.o
> > >  obj-$(CONFIG_SENSORS_STPDDC60)       += stpddc60.o
> > >  obj-$(CONFIG_SENSORS_TPS40422)       += tps40422.o
> > >  obj-$(CONFIG_SENSORS_TPS53679)       += tps53679.o
> > > +obj-$(CONFIG_SENSORS_TPS546D24)      += tps546d24.o
> > >  obj-$(CONFIG_SENSORS_UCD9000)        += ucd9000.o
> > >  obj-$(CONFIG_SENSORS_UCD9200)        += ucd9200.o
> > >  obj-$(CONFIG_SENSORS_XDPE122)        += xdpe12284.o
> > > diff --git a/drivers/hwmon/pmbus/tps546d24.c b/drivers/hwmon/pmbus/tps546d24.c
> > > new file mode 100644
> > > index 0000000..f6f79d3
> > > --- /dev/null
> > > +++ b/drivers/hwmon/pmbus/tps546d24.c
> > > @@ -0,0 +1,73 @@
> > > +// SPDX-License-Identifier: GPL-2.0+
> > > +/*
> > > + * Hardware monitoring driver for TEXAS TPS546D24 buck converter
> > > + */
> > > +
> > > +#include <linux/err.h>
> > > +#include <linux/i2c.h>
> > > +#include <linux/init.h>
> > > +#include <linux/kernel.h>
> > > +#include <linux/module.h>
> > > +#include <linux/pmbus.h>
> > > +#include "pmbus.h"
> > > +
> > > +static int tps546d24_read_byte_data(struct i2c_client *client, int page, int reg)
> > > +{
> > > +     int ret;
> > > +
> > > +     switch (reg) {
> > > +     case PMBUS_VOUT_MODE:
> > > +             ret = 0x17;
> > > +             break;
> > > +     default:
> > > +             ret = -ENODATA;
> > > +             break;
> > > +     }
> > > +     return ret;
> > > +}
> > > +
> > > +static struct pmbus_driver_info tps546d24_info = {
> > > +     .pages = 1,
> > > +     .format[PSC_VOLTAGE_IN] = linear,
> > > +     .format[PSC_VOLTAGE_OUT] = linear,
> > > +     .format[PSC_TEMPERATURE] = linear,
> > > +     .format[PSC_CURRENT_OUT] = linear,
> > > +     .func[0] = PMBUS_HAVE_VIN | PMBUS_HAVE_IIN |
> > > +         PMBUS_HAVE_IOUT | PMBUS_HAVE_VOUT |
> > > +             PMBUS_HAVE_STATUS_IOUT | PMBUS_HAVE_STATUS_VOUT |
> > > +             PMBUS_HAVE_TEMP | PMBUS_HAVE_STATUS_TEMP,
> > > +     .read_byte_data = tps546d24_read_byte_data,
> >
> > The chip supports multiple phases, and per-phase telemetry.
> > Have you considered supporting it ?
> >
> > > +};
> > > +
> > > +static int tps546d24_probe(struct i2c_client *client)
> > > +{
> > > +     return pmbus_do_probe(client, &tps546d24_info);
> > > +}
> > > +
> > > +static const struct i2c_device_id tps546d24_id[] = {
> > > +     {"tps546d24", 0},
> > > +     {}
> > > +};
> > > +MODULE_DEVICE_TABLE(i2c, tps546d24_id);
> > > +
> > > +static const struct of_device_id __maybe_unused tps546d24_of_match[] = {
> > > +     {.compatible = "tps546d24"},
> >
> > This needs a vendor prefix.
> >
> > > +     {}
> > > +};
> > > +
> > > +/* This is the driver that will be inserted */
> > > +static struct i2c_driver tps546d24_driver = {
> > > +     .driver = {
> > > +                .name = "tps546d24",
> > > +                .of_match_table = of_match_ptr(tps546d24_of_match),
> > > +        },
> > > +     .probe_new = tps546d24_probe,
> > > +     .id_table = tps546d24_id,
> > > +};
> > > +
> > > +module_i2c_driver(tps546d24_driver);
> > > +
> > > +MODULE_AUTHOR("Duke Du <dukedu83@...il.com>");
> > > +MODULE_DESCRIPTION("PMBus driver for TI tps546d24");
> > > +MODULE_LICENSE("GPL");
> > > +MODULE_IMPORT_NS(PMBUS);
> > > --
> > > 2.7.4
> > >

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