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SubjectRe: [PATCH 1/3] i3c: fix i2c and i3c scl rate by bus mode
On Mon, 22 Apr 2019 15:54:33 +0000
Vitor Soares <Vitor.Soares@synopsys.com> wrote:


> > > >
> > > > > {
> > > > > i3cbus->mode = mode;
> > > > >
> > > > > - if (!i3cbus->scl_rate.i3c)
> > > > > - i3cbus->scl_rate.i3c = I3C_BUS_TYP_I3C_SCL_RATE;
> > > > > -
> > > > > - 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;
> > > > > + 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 = i2c_scl_rate;
> > > > > + break;
> > > > > + case I3C_BUS_MODE_MIXED_SLOW:
> > > > > + if (!i3cbus->scl_rate.i2c)
> > > > > + i3cbus->scl_rate.i2c = i2c_scl_rate;
> > > > > + i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
> > > >
> > > > Maybe we should do
> > > >
> > > > if (!i3cbus->scl_rate.i3c ||
> > > > i3cbus->scl_rate.i3c > i3cbus->scl_rate.i2c)
> > > > i3cbus->scl_rate.i3c = i3cbus->scl_rate.i2c;
> > > >
> > > > Just in case the I3C rate forced by the user is lower than the max I2C
> > > > rate.
> > >
> > > That was something that I considered but TBH it isn't a real use case.
> >
> > 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 dts.
>
> I think the WARN_ON() is too evasive on the screen and won't provide the
> information we want.
> The dev_warn() should work perfectly here.
>
> 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__);

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.

> if (i3cbus->scl_rate.i2c != I3C_BUS_I2C_FM_SCL_RATE ||
> i3cbus->scl_rate.i2c != 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",
> __func__);

Is that really a problem? Having an i2c rate that is less than FM speed
sounds like a valid case to me.

>
> Maybe it make more sense to do this check on of_populate_i3c_bus(), what
> do you think?
>

No, we really want to have this check here, because we might support
other HW description formats at some point (board-files, ACPI, ...).

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