linux-kernel - RE: [PATCH v2 09/13] ARM: davinci - update the dm644x soc code to use common clk drivers

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Date:	Thu, 11 Oct 2012 14:58:26 +0000
From:	"Karicheri, Muralidharan" <m-karicheri2@...com>
To:	"Nori, Sekhar" <nsekhar@...com>
CC:	"mturquette@...aro.org" <mturquette@...aro.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Hilman, Kevin" <khilman@...com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-keystone@...t.ti.com - Linux developers for Keystone family of
	devices (May contain non-TIers)" <linux-keystone@...t.ti.com>,
	"linux-c6x-dev@...ux-c6x.org" <linux-c6x-dev@...ux-c6x.org>,
	"Chemparathy, Cyril" <cyril@...com>
Subject: RE: [PATCH v2 09/13] ARM: davinci - update the dm644x soc code to
 use common clk drivers

>> -----Original Message-----
>> From: Nori, Sekhar
>> Sent: Thursday, October 11, 2012 8:25 AM
>> To: Karicheri, Muralidharan
>> Cc: mturquette@...aro.org; arnd@...db.de; akpm@...ux-foundation.org;
>> shawn.guo@...aro.org; rob.herring@...xeda.com; linus.walleij@...aro.org;
>> viresh.linux@...il.com; linux-kernel@...r.kernel.org; Hilman, Kevin;
>> linux@....linux.org.uk; davinci-linux-open-source@...ux.davincidsp.com; linux-arm-
>> kernel@...ts.infradead.org; linux-keystone@...t.ti.com - Linux developers for Keystone
>> family of devices (May contain non-TIers); linux-c6x-dev@...ux-c6x.org; Chemparathy,
>> Cyril
>> Subject: Re: [PATCH v2 09/13] ARM: davinci - update the dm644x soc code to use
>> common clk drivers
>> 
>> Murali,
>> 
>> On 9/26/2012 11:40 PM, Murali Karicheri wrote:
>> > The clock tree for dm644x is defined using the new structure davinci_clk.
>> > The SoC specific code re-uses clk-fixed-rate, clk-divider and clk-mux
>> > drivers in addition to the davinci specific clk drivers,
>> > clk-davinci-pll and clk-davinci-psc. Macros are defined to define the
>> > various clocks in the SoC.
>> >
>> > Signed-off-by: Murali Karicheri <m-karicheri2@...com>
>> 
>> You have chosen to keep all clock related data in platform files while using the common
>> clock framework to provide just the infrastructure. If you look at how mxs and spear
>> have been migrated, they have migrated the soc specific clock data to drivers/clk as well.
>> See "drivers/clk/spear/spear3xx_clock.c" or "drivers/clk/mxs/clk-imx23.c 

I have to disagree on this one. I had investigated these code already and came up with a way that we can re-use code across all of the davinci platforms as well as other architectures that re-uses the clk hardware IPs. spear3xx_clock.c has initialization code for each of the platforms and so is the case with imx23.c. By using platform_data approach, we are able to define clks for each of the SoC and then use davinci_common_clk_init() to do initialize the clk drivers based on platform data. Later once we migrate to device tree, davinci_common_clk_init() will go way and also the clk structures defined in the SoC file. I have prototyped this on one of the device that I am working on. davinci_common_clk_init() will be replaced with a of_davinci_clk_init() that will use device tree to get all of the platform data for the clk providers and do the initialization based on that. See highbank_clocks_init() in clk-highbank.c. I have used this model for device
tree based clk initialization.

So it make sense to keep the design the way it is. Otherwise we will end up writing dm644x_clk_init(), dm355_clk_init(), etc for each of the platforms and these code will get thrown away once we migrate to
device tree. 

>>". I feel the
>> latter way is better and I also think it will simplify some of the look-up infrastructure you
>> had to build. This will also help some real code reduction from arch/arm/mach-davinci/.
>>

The look-up infrastructure is pretty much re-use of the existing code base in SoC specific file. About code reduction, I can't say I agree, as we need to add platform_specific clock initialization code if we follow spear3xx_clock.c model and end up probably adding more code. SoC specific file (for example dm644x.c) has only data structures and all of SoC will re-use davinci_common_clk_init() to do the initialization. So I am not sure how you conclude we will have code reduction?

- Murali

>> Thanks,
>> Sekhar