linux-kernel - Re: [PATCH] clk: register fixed-clock only if #clock-cells property is present

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Date:	Thu, 27 Mar 2014 12:14:01 +0100
From:	Boris BREZILLON <b.brezillon.dev@...il.com>
To:	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Fabio Estevam <festevam@...il.com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mike Turquette <mturquette@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>, t.figa@...sung.com,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...aro.org>,
	Shawn Guo <shawn.guo@...aro.org>,
	Sascha Hauer <kernel@...gutronix.de>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Olof Johansson <olof@...om.net>,
	'Arnd Bergmann' <arnd@...db.de>
Subject: Re: [PATCH] clk: register fixed-clock only if #clock-cells property
 is present

Hi Sylwester,

Le 27/03/2014 11:01, Sylwester Nawrocki a écrit :
> Hi Boris,
>
> On 27/03/14 08:58, Boris BREZILLON wrote:
>> This solution solve the problem for this specific case because clks are
>> declared in the correct order in imx DTs.
>> But, even with your patch I think we could see similar issues by
>> reordering DT nodes...
>>
>> The real problem here is that imx platform does not declare the CCM clocks
>> dependencies upon ckil, ckih1 and osc fixed clocks within the DT [1], and
>> retrieve these clocks when initializing the CCM clocks ([2] and [3]).
>>
>> We should try to a add these dependencies in the DT and see if it works.
> While presumably all of us agree the dependencies should be correctly
> specified in dts I think we should minimize possible regressions by
> keeping the clocks registration order as before, i.e. as parsed by the
> kernel from DT. Rather than explicitly reversing it, which does not gain
> us anything AFAICS. Instead we are seeing regressions where new kernels
> stop working with old dtbs.

I totally agree with you on this point: my patch is not a replacement of 
yours.
I just wanted to point out that we need to fix DT definitions to avoid these
kind of issues in the future.

>
> I'm going to resend the patch replacing list_add() with list_add_tail(),
> with this the mvebu platform would work and there should be no regression
> on imx and exynos.
>
> Please note that specifying dependencies between CCM on imx and the fixed
> clocks might not be enough. If the fixed clocks get matched on "fixed-clock"
> compatible some clock specifiers (i.e. those using phandle to the CCM) could
> get invalid, since the clocks won't get registered by the ccm driver, but by
> the regular fixed clock driver. That means a phandle to different node would
> need to be used to reference the fixed clock. I'm not sure if this is the case
> for imx, but changes may be needed all over various dts files.
> In addition, we should make sure the kernel works with current and modified
> dtbs.
>
>> [1] http://lxr.free-electrons.com/source/arch/arm/boot/dts/imx6sl.dtsi#L379
>> [2] http://lxr.free-electrons.com/source/arch/arm/mach-imx/clk-imx6q.c#L151
>> [3] http://lxr.free-electrons.com/source/arch/arm/mach-imx/clk.c#L30

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