Re: [PATCH v2 25/31] i2c: fsi: Calculate clock divider from local bus frequency

Guenter Roeck
2024-04-16T21:20:27Z

On Tue, Apr 16, 2024 at 01:09:04PM -0500, Eddie James wrote:
>
> On 4/15/24 17:11, Andi Shyti wrote:
> > Hi Eddie,
> >
> > > @@ -689,6 +692,20 @@ static int fsi_i2c_probe(struct device *dev)
> > > mutex_init(&i2c->lock);
> > > i2c->fsi = to_fsi_dev(dev);
> > > INIT_LIST_HEAD(&i2c->ports);
> > > + i2c->clock_div = I2C_DEFAULT_CLK_DIV;
> > > +
> > > + lbus = fsi_device_local_bus_frequency(i2c->fsi);
> > > + if (lbus) {
> > > + u32 clock = I2C_DEFAULT_CLK_RATE;
> > I don't see the need for initialization.
>
>
> Does device_property_read_u32 set clock if the property isn't found? If not,
> it needs to be initialized here. Or I can set it in an else statement from
> device_property_read_u32.
>
>
> >
> > > +
> > > + if (!device_property_read_u32(dev, "clock-frequency", &clock)) {
> > > + if (!clock)
> > > + clock = I2C_DEFAULT_CLK_RATE;
> > > + }

if (device_property_read_u32(dev, "clock-frequency", &clock) || !clock)
clock = I2C_DEFAULT_CLK_RATE;

> > > +
> > > + // i2c clock rate = local bus clock / (4 * (i2c clock div + 1))
> > You forgot to remove this.
>
>
> I actually meant to leave that comment to explain how the clock rate is
> calculated, as the reverse calculation in the code is a little more
> confusing.
>

Partially that is because you implemented DIV_ROUND_UP() manually.

>
> >
> > Andi
> >
> > > + i2c->clock_div = (((lbus + (clock - 1)) / clock) / 4) - 1;

= DIV_ROUND_UP(lbus, clock) / 4 - 1

Guenter