linux-kernel - Re: [PATCH] clk: respect the clock dependencies in of_clk

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Date:	Fri, 07 Feb 2014 13:16:36 -0300
From:	Emilio López <emilio@...pez.com.ar>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>
CC:	Mike Turquette <mturquette@...aro.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH] clk: respect the clock dependencies in of_clk_init

Hi Gregory,

El 07/02/14 12:12, Gregory CLEMENT escribió:
> On 07/02/2014 16:00, Emilio López wrote:
>> El 07/02/14 11:49, Gregory CLEMENT escribió:
>>> On 07/02/2014 15:43, Ezequiel Garcia wrote:
>>>> On Fri, Feb 07, 2014 at 09:24:30AM -0500, Jason Cooper wrote:
>>>>> On Fri, Feb 07, 2014 at 10:06:08AM -0300, Emilio López wrote:
>>>>>
>>>>> [snip a great explanation]
>>>>>
>>>>> Guys, can I get some Tested-by's on this?
>>>>>
>>>>
>>>> In case someone missed Emilio's comment about it, I gave his oneliner
>>>> a test on A370 Reference Design. It worked just as well as Sebastian's.
>>>
>>> Well ok it's working but this patch is not better than Sebastian, it is
>>> even worth. I don't think it is a good idea at all to totally ignore the
>>> information given by the device tree.
>>
>> With a bit more work, you can replace the clk_get magic with a call to
>> of_clk_get_parent_name() or similar to be able to keep overriding stuff
>> from DT. This way it would completely match the behaviour on
>> mvebu_coreclk_setup (default to "tclk", allow overriding with DT).
>>
>
> I think you didn't have a look on our implementation:

I did, several times in fact.

> the name of the clock
> are created by the driver during the initialization.

The name of the clock is always "tclk", as hardcoded on the driver, 
unless overridden via clock-output-names from DT (see 
mvebu_coreclk_setup). Currently none of your DT that I can see does 
this, so in practice it's always "tclk".

> That's why we need that
> the parent clock are initialized before the gating clock.

You don't really *need* that. The driver just does that because it may 
have been convenient at the time and it worked. Defaulting to "tclk" on 
mvebu_clk_gating_setup and overriding it if it turns out it has some 
other name on the DT (just like on mvebu_coreclk_setup!) should work as 
well, and doesn't require complex, bloaty, dependency management.

Rough, untested patch below, so you get the idea.

Cheers,

Emilio



---
  drivers/clk/mvebu/common.c | 13 +++++++------
  1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/clk/mvebu/common.c b/drivers/clk/mvebu/common.c
index 25ceccf..730625b 100644
--- a/drivers/clk/mvebu/common.c
+++ b/drivers/clk/mvebu/common.c
@@ -119,19 +119,20 @@ void __init mvebu_clk_gating_setup(struct 
device_node *np,
  				   const struct clk_gating_soc_desc *desc)
  {
  	struct clk_gating_ctrl *ctrl;
-	struct clk *clk;
  	void __iomem *base;
-	const char *default_parent = NULL;
+	struct of_phandle_args clkspec;
+	const char *default_parent = "tclk";
  	int n;

  	base = of_iomap(np, 0);
  	if (WARN_ON(!base))
  		return;

-	clk = of_clk_get(np, 0);
-	if (!IS_ERR(clk)) {
-		default_parent = __clk_get_name(clk);
-		clk_put(clk);
+	if (!of_parse_phandle_with_args(np, "clocks", "#clock-cells", 0, 
&clkspec)) {
+		of_property_read_string_index(clkspec.np, "clock-output-names",
+					      clkspec.args_count ? clkspec.args[0] : 0,
+					      &default_parent);
+		of_node_put(clkspec.np);
  	}

  	ctrl = kzalloc(sizeof(*ctrl), GFP_KERNEL);
-- 
1.8.5.3
--
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