On 7 August 2013 23:12, Stephen Warren swarren@wwwdotorg.org wrote:
On 08/07/2013 08:46 AM, Viresh Kumar wrote:
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.
:(
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.
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.
Btw, you must have some specific voltage level for each freq, we can get them here..
Similarly, we can't put invalid voltages into the DT, since if a later kernel version starts actually using that field, the HW will no longer work correctly. Unless perhaps we put 0 into the DT and make the binding define that 0 means "you can't change the voltage at all away from the boot value"?
Hmm.. so if you help me in getting actual voltage levels for these freqs then this problem will be resolved. Otherwise I can check what will happen if we pass zero to voltage.
Is the operating-points property documented in Documentation/devicetree/bindings/ somewhere?
Check above.
(Also Cc'ing the DT mailing list and maintainers)
Thanks.