Re: [PATCH 1/2] i2c: qup: Add device tree bindings information

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:

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Hi Kumar,

On Fri, 2013-08-30 at 10:21 -0500, Kumar Gala wrote: 

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On Aug 29, 2013, at 12:26 PM, Ivan T. Ivanov wrote:

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+
+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.

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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.

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+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