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

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Message-ID: <69bc0848-0698-b936-96a3-2257a5e27809@ti.com>
Date:   Thu, 5 Apr 2018 20:06:16 +0530
From:   Sekhar Nori <nsekhar@...com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
CC:     Michael Turquette <mturquette@...libre.com>,
        David Lechner <david@...hnology.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 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