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

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Date:   Thu, 5 Apr 2018 15:44:06 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Sekhar Nori <nsekhar@...com>
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

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.

Best regards,
Bartosz