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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: <154fe5b6-6a05-c2b7-3014-2f7b9c2049f9@samsung.com>
Date:   Mon, 29 Jun 2020 20:29:36 +0900
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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/

> 
> 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