Message-ID: <530231C5.8090905@free-electrons.com>
Date:	Mon, 17 Feb 2014 16:59:01 +0100
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
CC:	Jason Cooper <jason@...edaemon.net>,
	Emilio López <emilio@...pez.com.ar>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Mike Turquette <mturquette@...aro.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/4] clk: mvebu: fix clk init order

On 17/02/2014 16:44, Ezequiel Garcia wrote:
> On Mon, Feb 17, 2014 at 04:28:41PM +0100, Gregory CLEMENT wrote:
>> On 17/02/2014 16:21, Ezequiel Garcia wrote:
>>> On Mon, Feb 17, 2014 at 03:25:22PM +0100, Gregory CLEMENT wrote:
>>>> On 17/02/2014 15:13, Ezequiel Garcia wrote:
>>>>> On Wed, Feb 05, 2014 at 01:34:57PM -0500, Jason Cooper wrote:
>>>>>> On Sat, Jan 25, 2014 at 07:19:06PM +0100, Sebastian Hesselbarth wrote:
>>>>>>> This patch set fixes clk init order that went upside-down with
>>>>>>> v3.14. I haven't really investigated what caused this, but I assume
>>>>>>> it is related with DT node reordering by addresses.
>>>>>>>
>>>>>>> Anyway, with v3.14 for MVEBU SoCs, the clock gating driver gets
>>>>>>> registered before core clocks driver. Unfortunately, we cannot
>>>>>>> return -EPROBE_DEFER in drivers initialized by clk_of_init. As the
>>>>>>> init order for our drivers is always core clocks before clock gating,
>>>>>>> we maintain init order ourselves by hooking CLK_OF_DECLARE to one
>>>>>>> init function that will register core clocks before clock gating
>>>>>>> driver.
>>>>>>>
>>>>>>> This patch is based on pre-v3.14-rc1 mainline and should go in as
>>>>>>> fixes for it. As we now send MVEBU clk pull-requests to Mike directly,
>>>>>>> I suggest Jason picks it up as a topic branch.
>>>>>>>
>>>>>>> The patches have been boot tested on Dove and compile-tested only
>>>>>>> for Kirkwood, Armada 370 and XP.
>>>>>>>
>>>>>>> Sebastian Hesselbarth (4):
>>>>>>>   clk: mvebu: armada-370: maintain clock init order
>>>>>>>   clk: mvebu: armada-xp: maintain clock init order
>>>>>>>   clk: mvebu: dove: maintain clock init order
>>>>>>>   clk: mvebu: kirkwood: maintain clock init order
>>>>>>>
>>>>>>>  drivers/clk/mvebu/armada-370.c | 21 ++++++++++-----------
>>>>>>>  drivers/clk/mvebu/armada-xp.c  | 20 +++++++++-----------
>>>>>>>  drivers/clk/mvebu/dove.c       | 19 +++++++++----------
>>>>>>>  drivers/clk/mvebu/kirkwood.c   | 34 ++++++++++++++++------------------
>>>>>>>  4 files changed, 44 insertions(+), 50 deletions(-)
>>>>>>
>>>>>> Whole series applied to mvebu/clk-fixes.
>>>>>>
>>>>>
>>>>> Are we still in time to consider Emilio's oneline proposal?
>>>>> (Emilio: would you mind preparing a suitable patch against dove,
>>>>> kirkwood, armada370/xp, so we can see the real thing?).
>>>>
>>>> I am still strongly against this proposal because hard-coded the parent
>>>> clock name in the driver seems very wrong and moreover in some circumstances
>>>> (if there is no output-name, which is our default case) this proposal
>>>> just ignored the parent clock given by the device tree and this looked
>>>> more wrong.
>>>>
>>>
>>> So you're against the proposal as a permanent fix, *and* against the
>>> proposal as a workaround fix?
>>
>> Yes
>>
>>>
>>>>>
>>>>> Sebastian fix works perfect, and it easy to understand. However, it has
>>>>> quite a large diffstat. When compared to Emilio's oneline proposal, it
>>>>> seems to me it would be preferable, unless it's broken.
>>>>>
>>>>> Workaround or not, the fact is this code will be in v3.14, so maybe we
>>>>> can spend some time considering a cleaner option.
>>>>>
>>>
>>> Before discussing the solution as compared to your for-v3.15 clock
>>> registration order patch, I wanted to trigger some discussion around
>>> replacing this big and intrusive workaround with Emilio's oneline fix.
>>>
>>> Let's suppose we're considering them as workaround to live just one or
>>> two releases. Wouldn't it be better to take the least instrusive?
>>>
>>
>> The better solution is the one which doesn't add another regression and until
>> today I though we had an agreement to use the patch set from Sebastian. If
>> I remember well Jason had sent a pull request for it.
>>
>>
> 
> Right. If you think it adds a regression, then that's a perfectly valid reasons
> for nacking.
> 
> However, I'd like to double-check we have such a regression. I guess you're
> talking about the "tclk" name being hardcoded. IMHO, it's hardcoded in the
> driver in the first place:
> 
> void __init mvebu_coreclk_setup(struct device_node *np,
> 				const struct coreclk_soc_desc *desc)
> {
> 	const char *tclk_name = "tclk";
> [..] 


Here it is just about giving a name to a clock. As in the device tree
we only refer to the clock by index, the name don't matter.

> 
> So it wouldn't be too nasty?
> 
> I think you also mentioned the hypothetical case where the name
> is overloaded in the devicetree, so it's not "tclk", no? In that case,
> Emilio's fix would break.

I don't think I mentioned this case. I mentioned that this "fix" will
ignore the device tree.

> 
> However, we don't have such situation in our 'canonical' devicetrees,
> so if the devicetree is allowed to be change, it can also be
> changed to add clock-output-name's so the name doesn't have to be
> obtained after the clock is registered.
> 
> Which would solve it, no?

I really don't understand why you want introduce potential problem, just
to save a few line of code. A code that " works perfect, and it easy
to understand" as you wrote.




-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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