Re: [PATCHv2 4/5] clk: samsung: exynos5410: Add fixed rate clocks

From: Humberto Naves
Date: Thu Jul 31 2014 - 17:01:28 EST


On Thu, Jul 31, 2014 at 1:45 PM, Sylwester Nawrocki
<s.nawrocki@xxxxxxxxxxx> wrote:
> Can you explain what is rationale behind this change ? Is it related to
> suspend/resume ordering ?

I had forgotten, but now remember the reason why I did this. If you
see the current implementation of clk-exynos5410, you will notice it
heavily depends on the clock "fin_pll". On the other hand, this clock
exists because in the current dtb (exynos5410-smdk5410.dts), there is
a node fin_pll such as

fin_pll: xxti {
compatible = "fixed-clock";
clock-frequency = <24000000>;
clock-output-names = "fin_pll";
#clock-cells = <0>;

So far so good. But the real problem comes in when I check the rate of
fin_pll to determine if I should install the rate table or not (and I
really need this for my patch). More specifically

if (_get_rate("fin_pll") == 24 * MHZ) {
exynos5410_plls[apll].rate_table = apll_24mhz_tbl;
exynos5410_plls[cpll].rate_table = cpll_24mhz_tbl;
exynos5410_plls[kpll].rate_table = kpll_24mhz_tbl;
exynos5410_plls[dpll].rate_table = dpll_24mhz_tbl;
exynos5410_plls[epll].rate_table = epll_24mhz_tbl;
exynos5410_plls[ipll].rate_table = ipll_24mhz_tbl;

I *have* to determine if the rate of fin_pll is 24MHz, and this is
impossible to do if fin_pll is not available. Moreover, there is no
way I can ensure that the fixed clock provider for fin_pll was
initialized before mine, so there is chance that _get_rate won't work.
The only way I fix that is to set the dependency explicitly in the
dtb, by adding the fin_pll clock as required resource.

clock: clock-controller@10010000 {
compatible = "samsung,exynos5410-clock";
reg = <0x10010000 0x30000>;
#clock-cells = <1>;
/* Add the parent clock */
clocks = <&fin_pll>;
clock-names = "fin_pll";

But in any case, the bindings with the DTB must be changed one way or
another, because I *really* need to use fin_pll on my driver
registration. If you agree with this alternative solution I previously
described, I can change that in the next version of the patch series.

Best regards,

> Obviously it breaks the kernel/dtb compatibility. We should be moving
> in opposite direction, i.e. completely remove the custom samsung fixed
> rate clocks.
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