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

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Date:   Mon, 5 Mar 2018 10:23:55 -0600
From:   David Lechner <david@...hnology.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        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 03/05/2018 07:02 AM, Bartosz Golaszewski wrote:
> 2018-03-01 17:44 GMT+01:00 David Lechner <david@...hnology.com>:
>> 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
> 
> 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
> 

Thanks for continuing to dig into this. I think I know what needs to
be done now. I think I don't have the dependencies quite right where
the PSC clocks are being registered before the PLL clocks, in which
case they aren't getting the correct parent clock.