Re: [RFC 2/4] ARM: dts: Add ctrl-core DT node for DRA7

From: Archit Taneja <archit@ti.com>
To: Tero Kristo <t-kristo@ti.com>, Tony Lindgren <tony@atomide.com>,
	"paul@pwsan.com" <paul@pwsan.com>
Cc: linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	Rajendra Nayak <rnayak@ti.com>
Subject: Re: [RFC 2/4] ARM: dts: Add ctrl-core DT node for DRA7
Date: Thu, 8 May 2014 13:46:38 +0530	[thread overview]
Message-ID: <536B3D66.4020905@ti.com> (raw)
In-Reply-To: <536B380D.7000503@ti.com>

On Thursday 08 May 2014 01:23 PM, Tero Kristo wrote:
> On 05/08/2014 09:02 AM, Archit Taneja wrote:
>> On Tuesday 06 May 2014 07:56 PM, Tony Lindgren wrote:
>>> * Archit Taneja <archit@ti.com> [140505 22:24]:
>>>> Hi,
>>>>
>>>> On Monday 21 April 2014 08:40 PM, Tony Lindgren wrote:
>>>>> * Archit Taneja <archit@ti.com> [140420 22:16]:
>>>>>> Hi,
>>>>>>
>>>>>> On Friday 18 April 2014 10:48 PM, Tony Lindgren wrote:
>>>>>>> * Archit Taneja <archit@ti.com> [140416 06:20]:
>>>>>>>> Add DT node for the ctrl-core sub module of the DRA7 control
>>>>>>>> module. We map the
>>>>>>>> CTRL_MODULE_CORE address region up to 0x4a002d60, this region
>>>>>>>> contains register
>>>>>>>> fields which configure clocks. The remainder of the registers are
>>>>>>>> related to
>>>>>>>> pad configurations or cross-bar configurations, and therefore
>>>>>>>> aren't mapped.
>>>>>>>
>>>>>>> Can you please check if this can just use the existing
>>>>>>> regmap syscon mapping:
>>>>>>>
>>>>>>> syscon = <&dra7_ctrl_general>;
>>>>>>>
>>>>>>> See how the drivers/regulator/pbias-regulator.c is using the
>>>>>>> syscon to initialize a regulator and then omap_hsmmc.c just does
>>>>>>> the standard regulator calls.
>>>>>>
>>>>>> The thing is that this bit needs to be set before the the DSS
>>>>>> hwmods are
>>>>>> reset, and that happens very early. If we don't do this, DSS won't
>>>>>> reset
>>>>>> properly, and not get back to an idle state.
>>>>>>
>>>>>> I am not sure where I can configure the syscon register early
>>>>>> enough that it
>>>>>> happens before the hwmods are reset. With a syscon mapping, I guess
>>>>>> we would
>>>>>> access the register when the DSS driver is probed. But that's too
>>>>>> late for
>>>>>> us.
>>>>>>
>>>>>> Ideally, it would be much better to have a syscon mapping. Do you
>>>>>> have any
>>>>>> suggestions how this can be achieved very early in boot?
>>>>>
>>>>> It's best to move the reset and initialization of DSS happen later.
>>>>> I believe
>>>>> we already are resetting only some of the hwmods early on.
>>>>>
>>>>
>>>> I looked at this in some more detail. With the current hwmod
>>>> flags(HWMOD_INIT_NO_RESET/NO_IDLE), we still try to enable the IP,
>>>> it's just
>>>> the reset part(ocp reset/custom reset and sysc register) or the
>>>> disable part
>>>> that is skipped. hwmod still tries to enable the IP.
>>>>
>>>> This again results in the same issue.
>>>>
>>>> One thing which wasn't clear was that why do we enable a hwmod in the
>>>> first
>>>> place, if we know that we are going to skip reset?
>>>
>>> Probably to configure the idle bits. In general, we should configure the
>>> modules lazily as the driver probes as requested, and then idle the
>>> unused modules with a late_initcall.
>>
>> Okay, we were thinking of changing the hwmod code to skip enable for
>> hwmods(which have the HWMOD_INIT_NO_RESET flag) altogether. But that
>> doesn't seem like a viable option.
>>
>> I can't think of any other way of getting around this, besides making
>> control module a clock provider.
>>
>> Paul said that it's not that bad to make DRA7 CTRL module a clock
>> provider, but outside of PRCM code. I guess that would involve having
>> something along the lines of of_prcm_init() in mach-omap2/control.c
>
> That sounds like pretty much one of the things I have done here:
>
> https://github.com/t-kristo/linux-pm/tree/3.14-rc4-cm-prm-driver-wip
>
> The patches in their current form haven't been posted yet though, as
> they are waiting for some of the pre-reqs, but feel free to re-use
> something from here.

Ah nice, thanks!

Archit