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    SubjectRe: [PATCH 1/2] i2c: qup: Add device tree bindings information
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    Hi, 

    On Tue, 2013-09-10 at 08:59 -0500, Josh Cartwright wrote:
    > [Hmm. Fixing b0rked LKML address; that might explain why I am not
    > seeing Kumar's replies.]
    >

    Yes, sorry about this.

    > On Tue, Sep 10, 2013 at 03:08:57PM +0300, Ivan T. Ivanov wrote:
    > > Hi Kumar,
    > >
    > > On Fri, 2013-08-30 at 10:21 -0500, Kumar Gala wrote:
    > > > On Aug 29, 2013, at 12:26 PM, Ivan T. Ivanov wrote:
    > > > >>> +
    > > > >>> +Optional properties :
    > > > >>> + - Child nodes conforming to i2c bus binding
    > > > >>> + - clock-frequency : Desired I2C bus clock frequency in Hz. If
    > > > >>> + not set thedefault frequency is 100kHz
    > > > >>> + - qcom,src-freq : Frequency of the source clocking this bus in Hz.
    > > > >>> + Divider value is set based on soruce-frequency and
    > > > >>> + desired I2C bus frequency. If this value is not
    > > > >>> + provided, the source clock is assumed to be running
    > > > >>> + at 19.2 MHz.
    > > > >>
    > > > >> I'd spell out frequency instead of 'freq' to be consistent with 'clock-frequency'
    > > > >
    > > > > ok.
    > > > >
    > > > >>
    > > > >> Is the frequency of the 'iface' clock? Can we not use clk_get_rate?
    > > > >
    > > > > It is for 'core' clock. I think that for higher I2C bus frequencies,
    > > > > 'core' clock have to be higher, but I am not sure what is relation.
    > > >
    > > > Ok, can we use clk_get_rate on the 'core' clk to get its frequency instead of needing a DT prop for it?
    > >
    > > Probably I didn't explain it well. The 'core' clock have to be
    > > accelerated before higher bus frequencies could be achieved.
    >
    > I think what Kumar is suggesting is that the QUP driver not do an
    > explicit clk_set_rate() at all (which AFAICT is what's currently being
    > done to set the consuming clock to the rate specified in
    > 'qcom,src-freq'), but instead assume that the consuming clock has
    > already been setup properly. Then the driver just uses clk_get_rate()
    > and clock-frequency to calculate how to setup any internal dividers.

    Yes, I think I got it, but the point is that clock is not already set
    and it is driver responsibility to do that.

    >
    > > > >>> +Aliases: An alias may optionally be used to bind the I2C controller
    > > > >>> +to bus number. Aliases are of the form i2c<n> where <n> is an integer
    > > > >>> +representing the bus number to use.
    > > > >>> +
    > > > >>> +Example:
    > > > >>> +
    > > > >>> + aliases {
    > > > >>> + i2c0 = &i2c_A;
    > > > >>> + i2c1 = &i2c_B;
    > > > >>> + i2c2 = &i2c_C;
    > > > >>> + };
    > > > >>
    > > > >> What is the purpose here?
    > > > >
    > > > > Define on which I2C bus this controller operate. I2C client
    > > > > drivers usually do i2c_get_adapter(bus_number) before its
    > > > > registration. This is for drivers before invention of
    > > > > of_i2c_register_devices(), I believe.
    > > >
    > > > Since this is for upstream why dont we use of_i2c_register_devices() and remove this stuff related to aliases.
    > >
    > > Adapter driver already is using of_i2c_register_devices(). Also OF
    > > helper function will/or is already part of i2c_register_adapter().
    > > Attempt here was to make it compatible with older i2c client drivers.
    >
    > I agree with Kumar on removing this. If we decide it is something worth
    > keeping, logic to support it doesn't belong in the QUP driver, but in
    > the i2c core.

    I don't have strong objection here, will remove aliases support.

    Regards,
    Ivan
    >




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