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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>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode
Thread-Topic: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode
Thread-Index: AQHU87sLhgtQ1+d000+4YAeSeMHzMaY+J6iAgACom0D//+7fAIAJjifg///0oYCAADajAA==
Date:   Mon, 22 Apr 2019 17:54:29 +0000
Message-ID: <13D59CF9CEBAF94592A12E8AE55501350A61C415@DE02WEMBXB.internal.synopsys.com>
References: <cover.1555350118.git.vitor.soares@synopsys.com>
        <05fdeea79db83970e9ecb0d7045b4dd98f206f06.1555350118.git.vitor.soares@synopsys.com>
        <20190416075041.22f8e849@collabora.com>
        <13D59CF9CEBAF94592A12E8AE55501350A61596D@DE02WEMBXB.internal.synopsys.com>
        <20190416165250.0606e5a2@collabora.com>
        <13D59CF9CEBAF94592A12E8AE55501350A61B3B4@DE02WEMBXB.internal.synopsys.com>
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From: Boris Brezillon <boris.brezillon@collabora.com>
Date: Mon, Apr 22, 2019 at 17:07:15

> On Mon, 22 Apr 2019 15:54:33 +0000
> Vitor Soares <Vitor.Soares@synopsys.com> wrote:
>=20
>=20
> > > > >    =20
> > > > > >  {
> > > > > >  	i3cbus->mode =3D mode;
> > > > > > =20
> > > > > > -	if (!i3cbus->scl_rate.i3c)
> > > > > > -		i3cbus->scl_rate.i3c =3D I3C_BUS_TYP_I3C_SCL_RATE;
> > > > > > -
> > > > > > -	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;
> > > > > > +	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 i2c_scl_rate;
> > > > > > +		break;
> > > > > > +	case I3C_BUS_MODE_MIXED_SLOW:
> > > > > > +		if (!i3cbus->scl_rate.i2c)
> > > > > > +			i3cbus->scl_rate.i2c =3D i2c_scl_rate;
> > > > > > +		i3cbus->scl_rate.i3c =3D i3cbus->scl_rate.i2c;   =20
> > > > >=20
> > > > > Maybe we should do
> > > > >=20
> > > > > 		if (!i3cbus->scl_rate.i3c ||
> > > > > 		    i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> > > > > 			i3cbus->scl_rate.i3c =3D i3cbus->scl_rate.i2c;
> > > > > 					  =20
> > > > > Just in case the I3C rate forced by the user is lower than the ma=
x I2C
> > > > > rate.   =20
> > > >=20
> > > > That was something that I considered but TBH it isn't a real use ca=
se. =20
> > >=20
> > > Add a WARN_ON() to at least catch such inconsistencies. And maybe we
> > > should add a dev_warn() when the user-defined rates do not match
> > > the mode/LVR constraints. It's easy to do a mistake when writing a dt=
s. =20
> >=20
> > I think the WARN_ON() is too evasive on the screen and won't provide th=
e=20
> > information we want.
> > The dev_warn() should work perfectly here.
> >=20
> > 		if (i3cbus->scl_rate.i3c < i3cbus->scl_rate.i2c)
> > 			dev_warn(&i3cbus->cur_master->dev->dev,
> > 				     "%s: i3c-scl-hz lower then i2c-scl-hz\n",  __func__);
>=20
> Using dev_warn() sounds good, though I don't think you need the
> __func__ here. Also, please print the i2c/i3c rates in the message, and
> align the second line on the open parens.
>=20
> > 		if (i3cbus->scl_rate.i2c !=3D I3C_BUS_I2C_FM_SCL_RATE ||
> > 		    i3cbus->scl_rate.i2c !=3D I3C_BUS_I2C_FM_PLUS_SCL_RATE)
> > 			dev_warn(&i3cbus->cur_master->dev->dev,
> > 				     "%s: i2c-scl-hz not defined according MIPI I3C spec\n",=20
> > 				     __func__);
>=20
> Is that really a problem? Having an i2c rate that is less than FM speed
> sounds like a valid case to me.

I'm addressing the spec constrains.

In the practice it can be SM or even HS, it depends on the interface.

>=20
> >=20
> > Maybe it make more sense to do this check on of_populate_i3c_bus(), wha=
t=20
> > do you think?
> >=20
>=20
> No, we really want to have this check here, because we might support
> other HW description formats at some point (board-files, ACPI, ...).

Yes, you are right. I forgot that point.=20