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Date: Thu, 6 Jun 2019 17:16:55 +0000
From: Vitor Soares <Vitor.Soares@...opsys.com>
To: Boris Brezillon <boris.brezillon@...labora.com>,
Vitor Soares <Vitor.Soares@...opsys.com>
CC: "linux-i3c@...ts.infradead.org" <linux-i3c@...ts.infradead.org>,
"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
Boris Brezillon <bbrezillon@...nel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH v2 1/3] i3c: fix i2c and i3c scl rate by bus mode
From: Boris Brezillon <boris.brezillon@...labora.com>
Date: Thu, Jun 06, 2019 at 15:18:44
> On Thu, 6 Jun 2019 16:00:01 +0200
> Vitor Soares <Vitor.Soares@...opsys.com> wrote:
>
> > Currently the I3C framework limits SCL frequency to FM speed when
> > dealing with a mixed slow bus, even if all I2C devices are FM+ capable.
> >
> > The core was also not accounting for I3C speed limitations when
> > operating in mixed slow mode and was erroneously using FM+ speed as the
> > max I2C speed when operating in mixed fast mode.
> >
> > Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
> > Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> > Cc: Boris Brezillon <bbrezillon@...nel.org>
> > Cc: <stable@...r.kernel.org>
> > Cc: <linux-kernel@...r.kernel.org>
> > ---
> > Changes in v2:
> > Enhance commit message
> > Add dev_warn() in case user-defined i2c rate doesn't match LVR constraint
> > Add dev_warn() in case user-defined i3c rate lower than i2c rate.
> >
> > drivers/i3c/master.c | 61 +++++++++++++++++++++++++++++++++++++++++-----------
> > 1 file changed, 48 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> > index 5f4bd52..8cd5824 100644
> > --- a/drivers/i3c/master.c
> > +++ b/drivers/i3c/master.c
> > @@ -91,6 +91,12 @@ void i3c_bus_normaluse_unlock(struct i3c_bus *bus)
> > up_read(&bus->lock);
> > }
> >
> > +static struct i3c_master_controller *
> > +i3c_bus_to_i3c_master(struct i3c_bus *i3cbus)
> > +{
> > + return container_of(i3cbus, struct i3c_master_controller, bus);
> > +}
> > +
> > static struct i3c_master_controller *dev_to_i3cmaster(struct device *dev)
> > {
> > return container_of(dev, struct i3c_master_controller, dev);
> > @@ -565,20 +571,48 @@ static const struct device_type i3c_masterdev_type = {
> > .groups = i3c_masterdev_groups,
> > };
> >
> > -int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode)
> > +int i3c_bus_set_mode(struct i3c_bus *i3cbus, enum i3c_bus_mode mode,
> > + unsigned long max_i2c_scl_rate)
> > {
> > - i3cbus->mode = mode;
> >
> > - if (!i3cbus->scl_rate.i3c)
> > - i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > + struct i3c_master_controller *master = i3c_bus_to_i3c_master(i3cbus);
> >
> > - if (!i3cbus->scl_rate.i2c) {
> > - if (i3cbus->mode == I3C_BUS_MODE_MIXED_SLOW)
> > - i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> > - else
> > - i3cbus->scl_rate.i2c = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> > + i3cbus->mode = mode;
> > +
> > + switch (i3cbus->mode) {
> > + case I3C_BUS_MODE_PURE:
> > + if (!i3cbus->scl_rate.i3c)
> > + i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > + break;
> > + case I3C_BUS_MODE_MIXED_FAST:
> > + if (!i3cbus->scl_rate.i3c)
> > + i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > + if (!i3cbus->scl_rate.i2c)
> > + i3cbus->scl_rate.i2c = max_i2c_scl_rate;
> > + break;
> > + case I3C_BUS_MODE_MIXED_SLOW:
> > + if (!i3cbus->scl_rate.i2c)
> > + i3cbus->scl_rate.i2c = max_i2c_scl_rate;
> > + if (!i3cbus->scl_rate.i3c ||
> > + i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> > + i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
> > + break;
> > + default:
> > + return -EINVAL;
> > }
> >
> > + if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c)
> > + dev_warn(&master->dev,
> > + "i3c-scl-hz=%ld lower than i2c-scl-hz=%ld\n",
> > + i3cbus->scl_rate.i3c, i3cbus->scl_rate.i2c);
> > +
> > + if (i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE &&
> > + i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_PLUS_SCL_RATE &&
> > + i3cbus->mode != I3C_BUS_MODE_PURE)
>
> If you are so strict, there's clearly no point exposing an i2c-scl-hz
> property. I'm still not convinced having an i2c rate that's slower than
> what the I2C/I3C spec defines as the *typical* rate is a bad thing,
I'm not been strictive, I just inform the user about that case.
> just
> like I'm not convinced having an I3C rate that's slower than the I2C
> one is a problem (it's definitely a weird situation, but there's nothing
> preventing that in the spec).
You agree that there is no point for case where i3c rate < i2c rate yet
you are not convinced.
Do you thing that will be users for this case?
Anyway, this isn't a high requirement for me. The all point of this patch
is to introduce the limited bus configuration.
>
> > + dev_warn(&master->dev,
> > + "i2c-scl-hz=%ld not defined according MIPI I3C spec\n"
> > + , i3cbus->scl_rate.i2c);
>
> The comma should be on the previous line.
>
> > +
> > /*
> > * I3C/I2C frequency may have been overridden, check that user-provided
> > * values are not exceeding max possible frequency.
> > @@ -1966,9 +2000,6 @@ of_i3c_master_add_i2c_boardinfo(struct i3c_master_controller *master,
> > /* LVR is encoded in reg[2]. */
> > boardinfo->lvr = reg[2];
> >
> > - if (boardinfo->lvr & I3C_LVR_I2C_FM_MODE)
> > - master->bus.scl_rate.i2c = I3C_BUS_I2C_FM_SCL_RATE;
> > -
> > list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
> > of_node_get(node);
> >
> > @@ -2417,6 +2448,7 @@ int i3c_master_register(struct i3c_master_controller *master,
> > const struct i3c_master_controller_ops *ops,
> > bool secondary)
> > {
> > + unsigned long i2c_scl_rate = I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> > struct i3c_bus *i3cbus = i3c_master_get_bus(master);
> > enum i3c_bus_mode mode = I3C_BUS_MODE_PURE;
> > struct i2c_dev_boardinfo *i2cbi;
> > @@ -2466,9 +2498,12 @@ int i3c_master_register(struct i3c_master_controller *master,
> > ret = -EINVAL;
> > goto err_put_dev;
> > }
> > +
> > + if (i2cbi->lvr & I3C_LVR_I2C_FM_MODE)
> > + i2c_scl_rate = I3C_BUS_I2C_FM_SCL_RATE;
> > }
> >
> > - ret = i3c_bus_set_mode(i3cbus, mode);
> > + ret = i3c_bus_set_mode(i3cbus, mode, i2c_scl_rate);
> > if (ret)
> > goto err_put_dev;
> >
Best regards,
Vitor Soares
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