Re: [PATCH] i2c-qoriq: modified compatibility for correct prescaler

On Mon, Nov 17, 2014 at 07:28:03PM -0600, Scott Wood wrote:

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.

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?