Date:	Mon, 19 May 2014 12:40:59 +0530
From:	Rahul Sharma <rahul.sharma@...sung.com>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	Tomasz Stanislawski <t.stanislaws@...sung.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	PANKAJ KUMAR DUBEY <pankaj.dubey@...sung.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrzej Hajda <a.hajda@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	sunil joshi <joshi@...sung.com>
Subject: Re: [PATCH v3 1/3] phy: Add exynos-simple-phy driver

On 16 May 2014 20:19, Tomasz Figa <t.figa@...sung.com> wrote:
> On 16.05.2014 16:30, Rahul Sharma wrote:
>> On 16 May 2014 16:20, Tomasz Figa <t.figa@...sung.com> wrote:
>>> On 16.05.2014 12:35, Rahul Sharma wrote:
>>>> On 16 May 2014 15:12, Rahul Sharma <rahul.sharma@...sung.com> wrote:
>>>>> On 16 May 2014 03:14, Tomasz Figa <tomasz.figa@...il.com> wrote:
>>>>>> On 15.05.2014 06:01, Rahul Sharma wrote:
>>>> [snip]
>>>>>>>> the PHY provider.
>>>>>>>>
>>>>>>>
>>>>>>> Please correct me if I got you wrong. You want somthing like this:
>>>>>>>
>>>>>>> pmu_system_controller: system-controller@...40000 {
>>>>>>>          ...
>>>>>>>           simple_phys: simple-phys {
>>>>>>>                         compatible = "samsung,exynos5420-simple-phy";
>>>>>>>                         ...
>>>>>>>           };
>>>>>>> };
>>>>>>
>>>>>> Not exactly.
>>>>>>
>>>>>> What I meant is that the PMU node itself should be the PHY provider, e.g.
>>>>>>
>>>>>> pmu_system_controller: system-controller@...40000 {
>>>>>>         /* ... */
>>>>>>         #phy-cells = <1>;
>>>>>> };
>>>>>>
>>>>>> and then the PMU node should instantiate the Exynos simple PHY driver,
>>>>>> as this is a driver for a facility existing entirely inside of the PMU.
>>>>>> Moreover, the driver should be rather called Exynos PMU PHY.
>>>>>>
>>>>>> I know this isn't really possible at the moment, but with device tree we
>>>>>> must design things carefully, so it's better to take a bit more time and
>>>>>> do things properly.
>>>>>>
>>>>>> So my opinion on this is that there should be a central Exynos PMU
>>>>>> driver that claims the IO region and instantiates necessary subdrivers,
>>>>>> such as Exynos PMU PHY driver, Exynos CLKOUT driver, Exynos cpuidle
>>>>>> driver and more, similar to what is being done in drivers/mfd.
>>>>>
>>>>
>>>> Hi Tomasz,
>>>>
>>>> These PHYs are not part of PMU as such. I am not sure if it is correct to
>>>> probe them as phy provider for all these phys. Only relation of these phys with
>>>> the PMU is 'enable/disable control'.
>>>
>>> Well, in reality what is implemented by this driver is not even a PHY,
>>> just some kind of power controllers, which are contained entirely in the
>>> PMU.
>>>
>>
>> I agree. Actually the role of generic phy framework for these 'simple' phys is
>> only that much.
>>
>>>> Controlling this bit using regmap interface
>>>> still looks better to me.
>>>
>>> Well, when there is a choice between using regmap and not using regmap,
>>> I'd rather choose the latter. Why would you want to introduce additional
>>> abstraction layer if there is no need for such?
>>>
>>>>
>>>> IMHO Ideal method would be probing these PHYs independently and resolving
>>>> the necessary dependencies like syscon handle, clocks etc. This way we will
>>>> not be having any common phy provider for all these independent PHYs and it
>>>> would be clean to add each of these phy nodes in DT. Please see my original
>>>> comment below.
>>>>
>>>> http://lkml.iu.edu/hypermail/linux/kernel/1404.1/00701.html
>>>
>>> With the solution I proposed, you don't need any kind of dependencies
>>> for those simple power controllers. They are just single bits that don't
>>> need anything special to operate, except PMU clock running.
>>
>> In that case we can further trim it down and let the drivers use the regmap
>> interface to control this bit. Many drivers including HDMI, DP just need that
>> much functionality from the phy provider.
>
> Well, this is what several drivers already do, like USB PHY (dedicated
> IP block), watchdog (for watchdog mask), SATA PHY (dedicated IP block
> too) or will do, like I2C (for configuration of I2C mux on Exynos5).
>
> At least this would be consistent with them and wouldn't be an API
> abuse, so I'd be inclined to go this way more than introducing
> abstractions like this patch does.

Ok. I had already posted a patch for this at
http://www.spinics.net/lists/linux-samsung-soc/msg28049.html
I will revive that thread.

@Tomasz Stanislawski, Do you have different opinion here?

Regards,
Rahul Sharma.

>
> Best regards,
> Tomasz
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> dri-devel@...ts.freedesktop.org
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