linux-kernel - Re: [PATCH v2 2/2] clk: tegra20: Enable lock-status polling for PLLs

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Date:   Wed, 17 Oct 2018 14:41:35 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        "pdeschrijver@...dia.com" <pdeschrijver@...dia.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jonathanh@...dia.com" <jonathanh@...dia.com>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "pgaikwad@...dia.com" <pgaikwad@...dia.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] clk: tegra20: Enable lock-status polling for PLLs

On 10/17/18 1:59 PM, Marcel Ziswiler wrote:
> On Fri, 2018-08-31 at 12:29 +0300, Peter De Schrijver wrote:
>> On Thu, Aug 30, 2018 at 09:42:10PM +0300, Dmitry Osipenko wrote:
>>> Currently all PLL's on Tegra20 use a hardcoded delay despite of
>>> having
>>> a lock-status bit. The lock-status polling was disabled ~7 years
>>> ago
>>> because PLLE was failing to lock and was a suspicion that other
>>> PLLs
>>> might be faulty too. Other PLLs are okay, hence enable the lock-
>>> status
>>> polling for them. This reduces delay of any operation that require
>>> PLL
>>> to lock.
>>>
>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>> ---
>>>
>>> Changelog:
>>>
>>> v2:	Don't enable polling for PLLE as it known to not being
>>> able to lock.
>>>
>>
>> This isn't correct. The lock bit of PLLE can declare lock too early,
>> but the
>> PLL itself does lock.
> 
> Is there an errata documenting this? As I could not really find any
> mentioning of this anywhere at least up to the v11 from Dec 21, 2010 I
> still have access to.
> 
> BTW: It looks like also PLLA may not always lock properly with those
> changes. Is there anything known about that as well? Here is what I get
> on various Colibri T20 modules (while random other ones seem to work
> fine):
Could you please try to increase the timeout value?