linux-kernel - Re: [PATCH 0/3] ARM: OMAP5+: Support Duty Cycle Correction(DCC)

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Date:	Wed, 28 May 2014 07:49:06 -0500
From:	Nishanth Menon <nm@...com>
To:	Tero Kristo <t-kristo@...com>
CC:	<devicetree@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Benoît Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>, Paul <paul@...an.com>
Subject: Re: [PATCH 0/3] ARM: OMAP5+: Support Duty Cycle Correction(DCC)

On Mon 26 May 2014 01:32:08 AM CDT, Tero Kristo wrote:
> On 05/24/2014 12:07 AM, Mike Turquette wrote:
>> Quoting Nishanth Menon (2014-05-16 03:45:57)
>>> Hi,
>>>
>>> This patch series has been carried over in vendor kernel for quiet
>>> few years now.
>>>
>>> Unfortunately, it was very recently re-discovered and upstream kernel
>>> is noticed to be broken for OMAP5 1.5GHz - at least we are operating
>>> DPLL at frequency higher than what it was intended to be when CPUFreq
>>> is enabled. Thankfully, with nominal voltage(we dont use AVS yet in
>>> upstream for the mentioned platforms) and margins in trimming, we
>>> have so far not crashed - but I strongly suspect this might be some
>>> boundary case survival.
>>
>> DCC also exists in OMAP4. In some cases customers used it, in other
>> cases we just ran the PLL way out of spec and the mpu_clk would divide
>> by 2.
>>
>> Is this broken for OMAP4 as well?
>
> Yes, its broken. This series does not address the OMAP4 needs for it,
> but can be expanded later by just defining a proper clock type with
> OMAP4 specific DCC rate limits etc. for it. We would need properly
> functioning DVFS for OMAP4 panda first though I guess... (support for
> the TPS regulator.)

Panda does not need DCC. Panda uses 4430 and Panda-ES uses 4460. 
neither of which need DCC (DPLLs are trimmed for required frequencies 
there) - 4430 never had DCC, 4460 had broken DCC. 4470 (which is not 
upstream and does not have a panda variant) is the only one needing DCC 
at higher frequencies, and that needs an entirely different 
scheme(compared to OMAP5+) as mentioned by Tero if 4470 ever gets 
supported upstream.

--
Regards,
Nishanth Menon

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