linux-kernel - Re: [PATCH 1/2] ARM: EXYNOS: Get current parent clock for power domain on/off

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Message-id: <551E4B85.1000903@samsung.com>
Date:	Fri, 03 Apr 2015 10:12:53 +0200
From:	Andrzej Hajda <a.hajda@...sung.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
Cc:	Kukjin Kim <kgene@...nel.org>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 1/2] ARM: EXYNOS: Get current parent clock for power domain
 on/off

On 04/02/2015 02:44 PM, Krzysztof Kozlowski wrote:
> 2015-04-02 14:29 GMT+02:00 Javier Martinez Canillas
> <javier.martinez@...labora.co.uk>:
>> Hello Krzysztof,
>>
>> On 04/02/2015 10:06 AM, Krzysztof Kozlowski wrote:
>>> Using a fixed (by DTS) parent for clocks when turning on the power domain
>>> may introduce issues in other drivers. For example when such driver
>>> changes the parent during runtime and expects that he is the only place
>>> of such change.
>>>
>>> Do not rely entirely on DTS providing the fixed parent for such clocks.
>>> Instead if "pclkN" clock name is missing, grab a current parent of clock
>>> with clk_get_parent().

Hi Krzysztof,

I wonder if it wouldn't be better to drop entirely pclks. Power domains
should save/restore its previous state, setting fixed parents on domain
resume can fool drivers as you described earlier.

Regards
Andrzej

>>>
>>> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
>>> ---
>>>  Documentation/devicetree/bindings/arm/exynos/power_domain.txt | 8 +++++---
>>>  arch/arm/mach-exynos/pm_domains.c                             | 9 ++++++---
>>>  2 files changed, 11 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/arm/exynos/power_domain.txt b/Documentation/devicetree/bindings/arm/exynos/power_domain.txt
>>> index 5da38c5ed476..0fc1312f6fd5 100644
>>> --- a/Documentation/devicetree/bindings/arm/exynos/power_domain.txt
>>> +++ b/Documentation/devicetree/bindings/arm/exynos/power_domain.txt
>>> @@ -19,9 +19,11 @@ Optional Properties:
>>>       domains.
>>>  - clock-names: The following clocks can be specified:
>>>       - oscclk: Oscillator clock.
>>> -     - pclkN, clkN: Pairs of parent of input clock and input clock to the
>>> -             devices in this power domain. Maximum of 4 pairs (N = 0 to 3)
>>> -             are supported currently.
>>> +     - pclkN, clkN: Input clocks (clkN) to the devices in this power domain.
>>> +             Optionally with parrents (pclkN). If such parent is provided
>>> +             it will be used for reparenting the given clock when domain
>>> +             is turned on. Otherwise the parent before power down will be
>>> +             used. Maximum of 4 pairs (N = 0 to 3) are supported currently.
>>>       - asbN: Clocks required by asynchronous bridges (ASB) present in
>>>               the power domain. These clock should be enabled during power
>>>               domain on/off operations.
>>> diff --git a/arch/arm/mach-exynos/pm_domains.c b/arch/arm/mach-exynos/pm_domains.c
>>> index cbe56b35aea0..c55bcf52a6ad 100644
>>> --- a/arch/arm/mach-exynos/pm_domains.c
>>> +++ b/arch/arm/mach-exynos/pm_domains.c
>>> @@ -37,6 +37,7 @@ struct exynos_pm_domain {
>>>       struct clk *oscclk;
>>>       struct clk *clk[MAX_CLK_PER_DOMAIN];
>>>       struct clk *pclk[MAX_CLK_PER_DOMAIN];
>>> +     unsigned int pclk_dynamic:MAX_CLK_PER_DOMAIN;
>>>       struct clk *asb_clk[MAX_CLK_PER_DOMAIN];
>>>  };
>>>
>>> @@ -62,6 +63,9 @@ static int exynos_pd_power(struct generic_pm_domain *domain, bool power_on)
>>>               for (i = 0; i < MAX_CLK_PER_DOMAIN; i++) {
>>>                       if (IS_ERR(pd->clk[i]))
>>>                               break;
>>> +                     /* If parent was not set in DT, save current parent */
>>> +                     if (pd->pclk_dynamic & (1 << i))
>>
>> Small nit: I personally think that using the BIT(i) macro for shifting bits
>> is more readable but I guess is a matter of personal taste.
> 
> Right, it seems I always forget about BIT macro.
> I'll respin with BIT() and your review/tested tags.
> 
> Thanks for feedback and testing!
> 
> Best regards,
> Krzysztof
> 

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