Wolfgang, Scott,
On 12/11/2014 02:44 PM, Valentin Longchamp wrote:
Hi all,
Picking up this issue again.
On 11/26/2014 02:41 AM, Scott Wood wrote:
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On Tue, 2014-11-25 at 19:13 +0100, Wolfram Sang wrote:
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On Mon, Nov 17, 2014 at 07:28:03PM -0600, Scott Wood wrote:
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On Fri, 2014-11-14 at 09:28 +0100, Wolfram Sang wrote:
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If we're going to change the device tree I'd rather just add a property
to say what the prescaler is.
We would however, leave the boards' device trees that use things like
"fsl,mpc8543-i2c" as is and introduce the prescaler for the others requiring it.
Now the drawback is that the driver would require a change, to parse this
prescaler new prescaler property. Would this be OK from your point of view
Wolfram ? If yes, I will send the patches for it.
I don't think it is OK.
Why?
Because I thought it could be deduced. Then, a seperate property would
not be OK.
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I'd think it can be deduced from the compatible property.
For almost all existing device trees it cannot be.
Pity :( If we do introduce a new property, it should probably be
"clock-div". Grepping through binding documentation, that seems
accepted. We should ask DT maintainers, too, to be safe.
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If you want something that will work without changing device trees,
you'll need to use SVR to identify the SoC.
The driver is doing that already, see mpc_i2c_get_sec_cfg_8xxx(). Dunno
if it makes sense to add to it for consistency reasons?
That's not SVR, but sure. Better to avoid messing with existing device
trees.
What is then the agreement here ? Add a clock-div to the device trees ? Or do
something similar to mpc_i2c_get_sec_cfg_8xxx() ?
I think the clock-div property is better according to Freescale's AN 2919
section 3.1 Source clock. All the source clocks are fixed (with a clock-div of 2
in case of mpc8536/43/45/47/48/67/68/72, plus p2020) except for the mpc8533/44
where it can be 2 or 3, and that's what mpc_i2c_get_sec_cfg_8xxx() determines.
So mpc_i2c_get_sec_cfg_8xxx() should remain the exception and the other
prescaler values should be derived from an additional clock-div that must be
added in the respective device trees (at least for the qoriq devices, because
for instance mpc8543 already has the correct prescaler thanks to
mpc_i2c_data_8543 from i2c-mpc.c).
Do you have an opinion on the above ?
Valentin