linux-kernel - Re: [PATCH v7 10/42] clk: davinci: New driver for davinci PSC clocks

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Message-ID: <6bbe9bf3-24c1-acd9-200d-513520d34558@lechnology.com>
Date:   Thu, 1 Mar 2018 10:44:29 -0600
From:   David Lechner <david@...hnology.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     linux-clk@...r.kernel.org,
        linux-devicetree <devicetree@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Adam Ford <aford173@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 10/42] clk: davinci: New driver for davinci PSC clocks

On 03/01/2018 02:36 AM, Bartosz Golaszewski wrote:
> 2018-02-28 22:40 GMT+01:00 David Lechner <david@...hnology.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@...0000/1d0d000.serial        active