Hi Dirk,

On Thu, Jun 29, 2017 at 3:18 PM, Dirk Behme [off-list ref] wrote:

On 29.06.2017 13:18, Geert Uytterhoeven wrote:

quoted

On Thu, Jun 29, 2017 at 12:28 PM, Dirk Behme [off-list ref]
wrote:

quoted

On 29.06.2017 11:27, Geert Uytterhoeven wrote:

quoted

TL;DR: Clocks may be in use by another CPU not running Linux, while
Linux
disables them as being unused.

quoted

quoted

quoted

On r8a7795, there are several Cortex A cores running Linux, and a Cortex
R7
core which may run another OS.
This is an interesting issue, and relevant to other SoCs, too.

First of all, just the clocks we know (*) are used by the R7 side *and* are
disabled by the kernel (for a practical demo this are e.g. ~7 clocks).

(*) Yes, this is board (and R7 software) related. And yes, this might result
in board specific r8a7795_crit_mod_clks/r8a7795_crit_core_clks[] tables. So
yes, most probably device tree would be an option. While there is

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/clk/clk.c#n3402

unfortunately

a) its marked as "Do not use this function"

and

b) even if we would ignore (a) we couldn't figure how to use this for the
RCar3 clocks (being no clock expert)

You cannot, as it only supports the legacy one-clock-per-node style.
You can use it on e.g. sd2_clk in arch/arm/boot/dts/r8a7791.dtsi, until R-Car
Gen2 is switched to the new CPG/MSSR driver.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds