Date:   Mon, 29 Jun 2020 13:26:38 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Chanwoo Choi <cw00.choi@...sung.com>, Marc Zyngier <maz@...nel.org>
Cc:     Heiko Stübner <heiko@...ech.de>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        kernel-team@...roid.com,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] PM / devfreq: rk3399_dmc: Fix kernel oops when
 rockchip,pmu is absent

Hi Chanwoo,

On 29/6/20 13:29, Chanwoo Choi wrote:
> Hi Enric and Mark,
> 
> On 6/29/20 8:05 PM, Enric Balletbo i Serra wrote:
>> Hi Chanwoo and Marc,
>>
>> On 29/6/20 13:09, Chanwoo Choi wrote:
>>> Hi Enric,
>>>
>>> Could you check this issue? Your patch[1] causes this issue.
>>> As Marc mentioned, although rk3399-dmc.c handled 'rockchip,pmu'
>>> as the mandatory property, your patch[1] didn't add the 'rockchip,pmu'
>>> property to the documentation. 
>>>
>>
>> I think the problem is that the DT binding patch, for some reason, was missed
>> and didn't land. The patch seems to have all the required reviews and acks.
>>
>>   https://patchwork.kernel.org/patch/10901593/
>>
>> Sorry because I didn't notice this issue when 9173c5ceb035 landed. And thanks
>> for fixing the issue.
> 
> If the 'rockchip,pmu' propery is mandatory, instead of Mark's patch,
> we better to require the merge of patch[1] to DT maintainer.
> 
> [1] https://patchwork.kernel.org/patch/10901593/
> 

Give me some time to double check, because I think that at this point, is needed
on some devices with old firmware but not now. It's been a while since I worked
on this, but I suspect that being optional is the right way.

Maybe Heiko, who IIRC worked on TF-A has a more clear thought on this?

Thanks,
 Enric

>>
>> Best regards,
>>  Enric
>>
>>> [1] 9173c5ceb035 ("PM / devfreq: rk3399_dmc: Pass ODT
>>> and auto power down parameters to TF-A.")
>>>
>>>
>>> On 6/29/20 5:18 PM, Marc Zyngier wrote:
>>>> Hi Chanwoo,
>>>>
>>>> On Mon, 29 Jun 2020 03:43:37 +0100,
>>>> Chanwoo Choi <cw00.choi@...sung.com> wrote:
>>>>>
>>>>> Hi Marc,
>>>>>
>>>>> On 6/23/20 12:28 AM, Marc Zyngier wrote:
>>>>
>>>> [...]
>>>>
>>>>> It looks good to me. But, I think that it is not necessary
>>>>> fully kernel panic log about NULL pointer. It is enoughspsp
>>>>> just mentioning the NULL pointer issue without full kernel panic log.
>>>>
>>>> I personally find the backtrace useful as it allows people with the
>>>> same issue to trawl the kernel log and find whether it has already be
>>>> fixed upstream. But it's only me, and I'm not attached to it.
>>>>
>>>>> So, how about editing the patch description as following or others simply?
>>>>> and we need to add 'stable@...r.kernel.org' to Cc list for applying it
>>>>> to stable branch.
>>>>
>>>> Looks good to me.
>>>>
>>>>>
>>>>>
>>>>>   PM / devfreq: rk3399_dmc: Fix kernel oops when rockchip,pmu is absent
>>>>>
>>>>>     Booting a recent kernel on a rk3399-based system (nanopc-t4),
>>>>>     equipped with a recent u-boot and ATF results in the kernel panic
>>>>>     about NULL pointer issue.
>>>>
>>>> nit: "results in a kernel panic on dereferencing a NULL pointer".
>>>>
>>>>>
>>>>>     This turns out to be due to the rk3399-dmc driver looking for
>>>>>     an *undocumented* property (rockchip,pmu), and happily using
>>>>>     a NULL pointer when the property isn't there.
>>>>>
>>>>>     Instead, make most of what was brought in with 9173c5ceb035
>>>>>     ("PM / devfreq: rk3399_dmc: Pass ODT and auto power down parameters
>>>>>     to TF-A.") conditioned on finding this property in the device-tree,
>>>>>     preventing the driver from exploding.
>>>>>
>>>>>     Fixes: 9173c5ceb035 ("PM / devfreq: rk3399_dmc: Pass ODT and auto power down parameters to TF-A.")
>>>>>     Signed-off-by: Marc Zyngier <maz@...nel.org>
>>>>>     Signed-off-by: Chanwoo Choi <cw00.choi@...sung.com>
>>>>
>>>>
>>>> Note that the biggest issue is still there: the driver is using an
>>>> undocumented property, and this patch is just papering over it.
>>>> Since I expect this property to be useful for something, it would be
>>>> good for whoever knows what it does to document it.
>>>
>>> Hi Marc,
>>>
>>> You are right. We have to do two step:
>>> 1. Add missing explanation of 'rockchip,pmu' property to dt-binding document
>>> 2. If possible, add 'rockchip,pmu' property node to rk3399_dmc dt node.
>>>
>>> When I tried to find usage example of 'rockchip,pmu' property,
>>> I found them as following: The 'rockchip,pmu' property[2] indicates
>>> 'PMU (Power Management Unit)'. 
>>>
>>> $ grep -rn "rockchip,pmu" arch/arm64/boot/dts/
>>> arch/arm64/boot/dts/rockchip/px30.dtsi:1211:		rockchip,pmu = <&pmugrf>;
>>> arch/arm64/boot/dts/rockchip/rk3399.dtsi:1909:		rockchip,pmu = <&pmugrf>;
>>> arch/arm64/boot/dts/rockchip/rk3368.dtsi:807:		rockchip,pmu = <&pmugrf>;
>>>
>>> [2] the description of 'rockchip,pmu' property
>>> - https://protect2.fireeye.com/url?k=e55f0ba3-b8384f85-e55e80ec-0cc47a31384a-d9c5f6b28aba9be6&q=1&u=https%3A%2F%2Felixir.bootlin.com%2Flinux%2Fv5.7.2%2Fsource%2FDocumentation%2Fdevicetree%2Fbindings%2Fpinctrl%2Frockchip%2Cpinctrl.txt%23L40
>>>
>>>
>>> If don't receive the any reply, I'll add as following:
>>>
>>> cwchoi00@...n-linux-pc:~/kernel/git.kernel/linux.chanwoo$ d
>>> diff --git a/Documentation/devicetree/bindings/devfreq/rk3399_dmc.txt b/Documentation/devicetree/bindings/devfreq/rk3399_dmc.txt
>>> index 0ec68141f85a..161e60ea874b 100644
>>> --- a/Documentation/devicetree/bindings/devfreq/rk3399_dmc.txt
>>> +++ b/Documentation/devicetree/bindings/devfreq/rk3399_dmc.txt
>>> @@ -18,6 +18,8 @@ Optional properties:
>>>                          format depends on the interrupt controller.
>>>                          It should be a DCF interrupt. When DDR DVFS finishes
>>>                          a DCF interrupt is triggered.
>>> +- rockchip,pmu:                 Phandle to the syscon managing the "pmu general
>>> +                        register files".
>>>  
>>>  Following properties relate to DDR timing:
>>>  
>>>
>>>
>>
>>
> 
> 

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