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From:   Bartosz Golaszewski <brgl@bgdev.pl>
Date:   Mon, 5 Mar 2018 14:02:17 +0100
Message-ID: <CAMRc=Mdhi=byn4gPY6tVxgGjn9cgvc3smUkjV=Ku9i3euaZZtQ@mail.gmail.com>
Subject: Re: [PATCH v7 10/42] clk: davinci: New driver for davinci PSC clocks
To:     David Lechner <david@lechnology.com>
Cc:     Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        linux-clk@vger.kernel.org,
        linux-devicetree <devicetree@vger.kernel.org>,
        arm-soc <linux-arm-kernel@lists.infradead.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@codeaurora.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Sekhar Nori <nsekhar@ti.com>,
        Kevin Hilman <khilman@kernel.org>,
        Adam Ford <aford173@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>
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2018-03-01 17:44 GMT+01:00 David Lechner <david@lechnology.com>:
> On 03/01/2018 02:36 AM, Bartosz Golaszewski wrote:
>>
>> 2018-02-28 22:40 GMT+01:00 David Lechner <david@lechnology.com>:
>>>
>>> On 02/28/2018 06:38 AM, Bartosz Golaszewski wrote:
>>>>
>>>>
>>>>
>>>> I think I found the reason for the strange crashes we were
>>>> experiencing (emac core->name being NULL) thanks to Sekhar who pointed
>>>> me in the right direction.
>>>>
>>>> The mdio driver fails to probe with v7 due to the supplied clock rate
>>>> being wrong. Before failing we register the emac clock with
>>>> pm_clk_add_clk(). When clock_ops puts the clock, it decreases the
>>>> reference count of the clock, but we never actually increased it in
>>>> the first place in the line above. The core clock code then destroys
>>>> the associated clk_core structure. When the next user comes around (in
>>>> our case the clk debug functions) the system crashes.
>>>>
>>>> I believe there to be two issues: one is with v7 - we need to increase
>>>> the clock reference count in davinci_psc_genpd_attach_dev().
>>>>
>>>> Second is the error path in the clock framework - we should remove the
>>>> destroyed clk_core from the debug list, which is not being done now.
>>>>
>>>> Why we even need to track the refcount of clk_core is a mistery for me
>>>> though. Stephen, Mike?
>>>>
>>>> Best regards,
>>>> Bartosz Golaszewski
>>>
>>>
>>>
>>> Great find. I figured it had to be something like this, but I wasn't
>>> able to reproduce the problem yet.
>>>
>>> I suppose it is time to spin up a v8 with some fixes.
>>
>>
>> I still don't know why the mdio clock rate is much lower than in
>> mainline though. Any ideas?
>>
>> Thanks,
>> Bart
>>
>
> Now that you have fixed the crash, can you answer the questions I have
> asked earlier?
>
>> Can you post the output of this command so that I can see how your
>
> clocks are setup:
>
> cat /sys/kernel/debug/clk/clk_summary
>
>> Using your workaround, can you run:
>
>
> cat /sys/kernel/debug/pm_genpd/pm_genpd_summary
>
> If you see:
>   1e27000.clock-controller: emac  off-0
>
> then genpd is not working like it is supposed to. You should see something
> like this for device that are working:
>           1e27000.clock-controller: uart2  on
>     /devices/platform/soc@1c00000/1d0d000.serial        active

Hi David, Sekhar,

I tried booting the board today over tftp but didn't succeed. I then
switched to a normal boot from SD card and the boot process froze at
the same moment (right after the DHCP config, or after rtc config if I
disabled DHCP in bootargs). I then realized that the emac clock can't
be the culprit. After some digging I found out that the late_initcall
to clk_disable_unused() disables sysclk6 - the parent of the arm
clock, which of course freezes the device.

If I remove the call to clk_disable_unused(), I can boot just fine.

The following other clocks are disabled before pll0_sysclk6:
pll1_sysclk3
pll0_obsclk
pll0_sysclk7

davinci_lpsc_clk_enable() is never called for these clocks - in fact
it's not called for any parent that's not explicitly defined in
psc-da850.c - I believe this may be one of the reasons. I will get
back to debugging it tomorrow.

Best regards,
Bartosz Golaszewski