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

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Message-ID: <53DAB04A.90005@gmail.com>
Date:	Thu, 31 Jul 2014 23:08:26 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Humberto Naves <hsnaves@...il.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>
CC:	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, Kukjin Kim <kgene.kim@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>,
	Thomas Abraham <ta.omasab@...il.com>,
	Andreas Farber <afaerber@...e.de>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>
Subject: Re: [PATCHv2 4/5] clk: samsung: exynos5410: Add fixed rate clocks

Humberto,

On 31.07.2014 23:01, Humberto Naves wrote:
> Hi,
> 
> On Thu, Jul 31, 2014 at 1:45 PM, Sylwester Nawrocki
> <s.nawrocki@...sung.com> 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@...10000 {
>                       compatible = "samsung,exynos5410-clock";
>                       reg = <0x10010000 0x30000>;
>                       #clock-cells = <1>;
>                       /* Add the parent clock */
>                       clocks = <&fin_pll>;
>                       clock-names = "fin_pll";
>               };

This is the correct solution to your problem. The clocks and clock-names
properties should have been there from the beginning but apparently this
has been missed in review. Also see below.

> 
> 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.

This is a backwards compatible change. On DTBs without clocks and
clock-names properties the PLL tables simply won't be registered which
is exactly the same behavior we have now without any tables in the
driver at all.

> If you agree with this alternative solution I previously
> described, I can change that in the next version of the patch series.

Please update the dts instead, in the way you pointed above.

Best regards,
Tomasz
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