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Subject: Re: [PATCH v2] PM / devfreq: rk3399_dmc: Fix kernel oops when
 rockchip,pmu is absent
To:     Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Marc Zyngier <maz@kernel.org>
Cc:     =?UTF-8?Q?Heiko_St=c3=bcbner?= <heiko@sntech.de>,
        MyungJoo Ham <myungjoo.ham@samsung.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        kernel-team@android.com,
        "stable@vger.kernel.org" <stable@vger.kernel.org>
From:   Chanwoo Choi <cw00.choi@samsung.com>
Organization: Samsung Electronics
Message-ID: <566d2f93-b5ff-b583-3965-83d4b9188c36@samsung.com>
Date:   Mon, 29 Jun 2020 21:12:18 +0900
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Hi Enric,

On 6/29/20 8:26 PM, Enric Balletbo i Serra wrote:
> 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.

OK. Thanks for your reply.

> 
> 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@samsung.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@vger.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@kernel.org>
>>>>>>     Signed-off-by: Chanwoo Choi <cw00.choi@samsung.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@chan-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:
>>>>  
>>>>
>>>>
>>>
>>>
>>
>>
> 
> 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics