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From:   Vitor Soares <Vitor.Soares@synopsys.com>
To:     Boris Brezillon <boris.brezillon@collabora.com>,
        Vitor Soares <Vitor.Soares@synopsys.com>
CC:     "linux-i3c@lists.infradead.org" <linux-i3c@lists.infradead.org>,
        "Joao.Pinto@synopsys.com" <Joao.Pinto@synopsys.com>,
        Boris Brezillon <bbrezillon@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: RE: [PATCH v2 1/3] i3c: fix i2c and i3c scl rate by bus mode
Thread-Topic: [PATCH v2 1/3] i3c: fix i2c and i3c scl rate by bus mode
Thread-Index: AQHVHGF3lXrsgZbBP0uzVGVfPAtbX6aOizQAgABOUdA=
Date:   Thu, 6 Jun 2019 17:16:55 +0000
Message-ID: <13D59CF9CEBAF94592A12E8AE55501350AABE7FC@DE02WEMBXB.internal.synopsys.com>
References: <cover.1559821227.git.vitor.soares@synopsys.com>
        <47de89f2335930df0ed6903be9afe6de4f46e503.1559821228.git.vitor.soares@synopsys.com>
 <20190606161844.4a6b759c@collabora.com>
In-Reply-To: <20190606161844.4a6b759c@collabora.com>
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From: Boris Brezillon <boris.brezillon@collabora.com>
Date: Thu, Jun 06, 2019 at 15:18:44

> On Thu,  6 Jun 2019 16:00:01 +0200
> Vitor Soares <Vitor.Soares@synopsys.com> wrote:
>=20
> > 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.
> >=20
> > 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.
> >=20
> > Fixes: 3a379bbcea0a ("i3c: Add core I3C infrastructure")
> > Signed-off-by: Vitor Soares <vitor.soares@synopsys.com>
> > Cc: Boris Brezillon <bbrezillon@kernel.org>
> > Cc: <stable@vger.kernel.org>
> > Cc: <linux-kernel@vger.kernel.org>
> > ---
> > Changes in v2:
> >   Enhance commit message
> >   Add dev_warn() in case user-defined i2c rate doesn't match LVR constr=
aint
> >   Add dev_warn() in case user-defined i3c rate lower than i2c rate.
> >=20
> >  drivers/i3c/master.c | 61 +++++++++++++++++++++++++++++++++++++++++---=
--------
> >  1 file changed, 48 insertions(+), 13 deletions(-)
> >=20
> > 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);
> >  }
> > =20
> > +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 *d=
ev)
> >  {
> >  	return container_of(dev, struct i3c_master_controller, dev);
> > @@ -565,20 +571,48 @@ static const struct device_type i3c_masterdev_typ=
e =3D {
> >  	.groups	=3D i3c_masterdev_groups,
> >  };
> > =20
> > -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 =3D mode;
> > =20
> > -	if (!i3cbus->scl_rate.i3c)
> > -		i3cbus->scl_rate.i3c =3D I3C_BUS_TYP_I3C_SCL_RATE;
> > +	struct i3c_master_controller *master =3D i3c_bus_to_i3c_master(i3cbus=
);
> > =20
> > -	if (!i3cbus->scl_rate.i2c) {
> > -		if (i3cbus->mode =3D=3D I3C_BUS_MODE_MIXED_SLOW)
> > -			i3cbus->scl_rate.i2c =3D I3C_BUS_I2C_FM_SCL_RATE;
> > -		else
> > -			i3cbus->scl_rate.i2c =3D I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> > +	i3cbus->mode =3D mode;
> > +
> > +	switch (i3cbus->mode) {
> > +	case I3C_BUS_MODE_PURE:
> > +		if (!i3cbus->scl_rate.i3c)
> > +			i3cbus->scl_rate.i3c =3D I3C_BUS_TYP_I3C_SCL_RATE;
> > +		break;
> > +	case I3C_BUS_MODE_MIXED_FAST:
> > +		if (!i3cbus->scl_rate.i3c)
> > +			i3cbus->scl_rate.i3c =3D I3C_BUS_TYP_I3C_SCL_RATE;
> > +		if (!i3cbus->scl_rate.i2c)
> > +			i3cbus->scl_rate.i2c =3D max_i2c_scl_rate;
> > +		break;
> > +	case I3C_BUS_MODE_MIXED_SLOW:
> > +		if (!i3cbus->scl_rate.i2c)
> > +			i3cbus->scl_rate.i2c =3D max_i2c_scl_rate;
> > +		if (!i3cbus->scl_rate.i3c ||
> > +		    i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> > +			i3cbus->scl_rate.i3c =3D i3cbus->scl_rate.i2c;
> > +		break;
> > +	default:
> > +		return -EINVAL;
> >  	}
> > =20
> > +	if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c)
> > +		dev_warn(&master->dev,
> > +			 "i3c-scl-hz=3D%ld lower than i2c-scl-hz=3D%ld\n",
> > +			 i3cbus->scl_rate.i3c, i3cbus->scl_rate.i2c);
> > +
> > +	if (i3cbus->scl_rate.i2c !=3D I3C_BUS_I2C_FM_SCL_RATE &&
> > +	    i3cbus->scl_rate.i2c !=3D I3C_BUS_I2C_FM_PLUS_SCL_RATE &&
> > +	    i3cbus->mode !=3D I3C_BUS_MODE_PURE)
>=20
> 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,=20

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=20
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=20
is to introduce the limited bus configuration.

>=20
> > +		dev_warn(&master->dev,
> > +			 "i2c-scl-hz=3D%ld not defined according MIPI I3C spec\n"
> > +			 , i3cbus->scl_rate.i2c);
>=20
> The comma should be on the previous line.
>=20
> > +
> >  	/*
> >  	 * I3C/I2C frequency may have been overridden, check that user-provid=
ed
> >  	 * 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 =3D reg[2];
> > =20
> > -	if (boardinfo->lvr & I3C_LVR_I2C_FM_MODE)
> > -		master->bus.scl_rate.i2c =3D I3C_BUS_I2C_FM_SCL_RATE;
> > -
> >  	list_add_tail(&boardinfo->node, &master->boardinfo.i2c);
> >  	of_node_get(node);
> > =20
> > @@ -2417,6 +2448,7 @@ int i3c_master_register(struct i3c_master_control=
ler *master,
> >  			const struct i3c_master_controller_ops *ops,
> >  			bool secondary)
> >  {
> > +	unsigned long i2c_scl_rate =3D I3C_BUS_I2C_FM_PLUS_SCL_RATE;
> >  	struct i3c_bus *i3cbus =3D i3c_master_get_bus(master);
> >  	enum i3c_bus_mode mode =3D I3C_BUS_MODE_PURE;
> >  	struct i2c_dev_boardinfo *i2cbi;
> > @@ -2466,9 +2498,12 @@ int i3c_master_register(struct i3c_master_contro=
ller *master,
> >  			ret =3D -EINVAL;
> >  			goto err_put_dev;
> >  		}
> > +
> > +		if (i2cbi->lvr & I3C_LVR_I2C_FM_MODE)
> > +			i2c_scl_rate =3D I3C_BUS_I2C_FM_SCL_RATE;
> >  	}
> > =20
> > -	ret =3D i3c_bus_set_mode(i3cbus, mode);
> > +	ret =3D i3c_bus_set_mode(i3cbus, mode, i2c_scl_rate);
> >  	if (ret)
> >  		goto err_put_dev;
> > =20

Best regards,
Vitor Soares