linux-kernel - Re: [PATCH v3 1/3] phy: Add exynos-simple-phy driver

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Date:	Mon, 19 May 2014 12:54:50 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Rahul Sharma <rahul.sharma@...sung.com>,
	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>,
	PANKAJ KUMAR DUBEY <pankaj.dubey@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	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 19.05.2014 09:10, Rahul Sharma wrote:
> 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.

Looks good to me.

> 
> @Tomasz Stanislawski, Do you have different opinion here?

I'm afraid Tomasz might not be very responsive during next few days, as
he is on a business trip. You might be able to reach him on our internal
communicator, though.

Best regards,
Tomasz
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