Re: [PATCH] cpufreq: Add Kryo CPU scaling driver

Sudeep Holla
2018-05-22T09:12:46Z

On 22/05/18 07:56, ilialin@codeaurora.org wrote:
>
>
>> -----Original Message-----
>> From: Sudeep Holla <sudeep.holla@arm.com>
>> Sent: Monday, May 21, 2018 16:05

[...]

>>
>>
>> That may be true and I am not that bothered about it. But assuming physical
>> ordering from the logical cpu number is *incorrect* and will break if kernel
>> decides to change the allocation algorithm. Kernel provides no guarantee on
>> that, so you need to depend on some physical ID or may be DT to achieve
>> what your want. But the current code as it stands is wrong.
>
> Got your point. In fact CPUs are numbered 0-3 and ordered into 2 clusters in the DT:
>
> cpus {
> #address-cells = <2>;
> #size-cells = <0>;
>
> CPU0: cpu@0 {
> ...
> reg = <0x0 0x0>;
> ...
> };
>
> CPU1: cpu@1 {
> ...
> reg = <0x0 0x1>;
> ...
> };
>
> CPU2: cpu@100 {
> ...
> reg = <0x0 0x100>;
> ...
> };
>
> CPU3: cpu@101 {
> ...
> reg = <0x0 0x101>;
> ...
> };
>
> cpu-map {
> cluster0 {
> core0 {
> cpu = <&CPU0>;
> };
>
> core1 {
> cpu = <&CPU1>;
> };
> };
>
> cluster1 {
> core0 {
> cpu = <&CPU2>;
> };
>
> core1 {
> cpu = <&CPU3>;
> };
> };
> };
> };
>
> As far, as I understand, they are probed in the same order.

Yes that's correct today, will that have to remain same for ever ?
No it's not user ABI and kernel can decide to change the allocation
order. What if for some reason one/more CPUs fails to boot or even
configured not to boot ?

> However, to be certain that the physical CPU is the one I intend to
> configure, I have to fetch the device structure pointer for the cpu-map ->
> clusterX -> core0 -> cpu path. Could you suggest a kernel API to do
> that?
>

Let's rewind a bit. Do you supply OPPs only on CPU0 and CPU2 ?
If yes, that's again wrong. Simple solution is to parse all logical
CPUs and skip if the share OPPs with some other CPUs. I think that
logic already exists in OPP library IIRC.

--
Regards,
Sudeep