linux-kernel - Re: [PATCH v5 12/44] clk: davinci: Add platform information for TI DA850 PSC

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Message-ID: <366610a6-8983-d744-01e5-a00592bef479@lechnology.com>
Date:   Thu, 5 Apr 2018 10:37:35 -0500
From:   David Lechner <david@...hnology.com>
To:     Sekhar Nori <nsekhar@...com>, Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Michael Turquette <mturquette@...libre.com>,
        linux-clk <linux-clk@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...nel.org>,
        Adam Ford <aford173@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 12/44] clk: davinci: Add platform information for TI
 DA850 PSC

On 04/05/2018 09:36 AM, Sekhar Nori wrote:
> On Thursday 05 April 2018 07:14 PM, Bartosz Golaszewski wrote:
>> 2018-04-05 15:09 GMT+02:00 Sekhar Nori <nsekhar@...com>:
>>> Hi Bartosz,
>>>
>>> On Friday 09 February 2018 10:18 PM, Michael Turquette wrote:
>>>> On Fri, Feb 9, 2018 at 8:22 AM, Bartosz Golaszewski <brgl@...ev.pl> wrote:
>>>>> 2018-01-08 3:17 GMT+01:00 David Lechner <david@...hnology.com>:
>>>
>>>>> Hi David,
>>>>>
>>>>> I've been working on moving the genpd code from its own driver to the
>>>>> psc one. I couldn't get the system to boot though and problems
>>>>> happened very early in the boot sequence. I struggled to figure out
>>>>> what's happening, but eventually I noticed that psc uses
>>>>> CLK_OF_DECLARE() to initialize clocks. The functions registered this
>>>>> way are called very early in the boot sequence, way before
>>>>> late_initcall() in which the genpd framework is initialized. This of
>>>
>>> late_initcall() is too late for genpd to be initialized. As you may have
>>> seen with the latest set of patches, we have problems with timer
>>> initialization. After converting to platform devices, PSC and PLL clocks
>>> get initialized post time_init(). We are working that around using
>>> fixed-clocks, which hopefully will work (I still need to test many of
>>> the affected platforms).
>>>
>>> Can you please reply with the exact issue you faced with genpd framework
>>> initialization so we do have that on record.
>>>
>>
>> The exact issue manifested itself in a NULL-pointer dereference panic
>> when I tried moving the genpd code I had initially implemented as a
>> separate platform driver to what I believe was v6 or v7 of David's
>> series (before the psc driver became a platform driver, when it was
>> still using CLK_OF_DECLARE()). When I had tested a simple conversion
>> of that version to a platform_driver, genpd worked fine.
>>
>> I don't have the stack traces from these panics, but I recall some
>> debugfs functions being involved and the genpd late_initcalls are
>> related to debugfs. Looking at it now I don't see how exactly it could
>> fail though.
> 
> Do you have the code where you faced the problem stashed somewhere? I am
> not (yet) advocating going back to CLK_OF_DECLARE(). But there is a
> definite issue with timer being ready when not using CLK_OF_DECLARE().
> So, I want to make sure there the reason why we are going down the
> platform device path is a amply clear.
> 
> Thanks,
> Sekhar
> 
This is the thread that led to the conversion to platform devices:

https://lkml.org/lkml/2018/2/9/541