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    SubjectRe: [PATCH v2 25/31] i2c: fsi: Calculate clock divider from local bus frequency
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    On 4/16/24 16:20, Guenter Roeck wrote:
    > 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;


    Nice one, thanks.


    >
    >>>> +
    >>>> + // 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.


    Thanks Guenter, good point.


    Eddie


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

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