[PATCH 2/6] ARM: Tegra: Add CPU's OPPs for using cpufreq-cpu0 driver
From: Stephen Warren <hidden>
Date: 2013-08-07 18:55:22
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linux-pm, lkml
On 08/07/2013 12:06 PM, Viresh Kumar wrote:
On 7 August 2013 23:12, Stephen Warren [off-list ref] wrote:quoted
On 08/07/2013 08:46 AM, Viresh Kumar wrote:quoted
cpufreq-cpu0 driver needs OPPs to be present in DT which can be probed by it to get frequency table. This patch adds OPPs and clock-latency to tegra cpu0 node for multiple SoCs. Voltage levels aren't used until now for tegra and so a flat value which would eventually be ignored is used to represent voltage.This patch is problematic w.r.t. DT being an ABI.:(quoted
We can certainly add new optional properties to a DT binding that enable new features. However, a new version of a binding can't require new properties to exist that didn't before, since that means that old DTs won't work with new kernels that require the new properties.To be honest I didn't get it completely. You meant operating-points wasn't present before? Its here: Documentation/devicetree/bindings/cpufreq/cpufreq-cpu0.txt Documentation/devicetree/bindings/power/opp.txt Or you meant, Tegra never required voltage levels and we are getting them in here.
The current Tegra *.dts files do not contain this property. The current Tegra *.dts files must continue to work without modification in future kernels.
quoted
As such, I believe we do need some Tegra-specific piece of code that defines these OPP tables in the kernel, so that the operating-points property is not needed.Generic cpufreq driver depends on OPP library and so somebody has to provide them. Now you can do it by calling opp_add() for each OPP you have or otherwise.
Sure. That's what the Tegra-specific cpufreq driver should do. It should be the top-level cpufreq driver. If parts of the code can be implemented by library functions or a core parameterizable driver, then presumably the Tegra driver would simply exist to provide those parameters and/or callback functions to the generic driver.
Btw, you must have some specific voltage level for each freq, we can get them here..
Yes, I'm sure we do, but I have no idea what they are:-( It may even be board-specific or SoC-SKU-specific. I think we should defer this aspect for now.