linux-kernel - Re: [PATCH v2] PM / devfreq: rk3399_dmc: Fix kernel oops when rockchip,pmu is absent

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Date:   Mon, 29 Jun 2020 20:09:12 +0900
From:   Chanwoo Choi <cw00.choi@...sung.com>
To:     Marc Zyngier <maz@...nel.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>
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 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. 

[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://elixir.bootlin.com/linux/v5.7.2/source/Documentation/devicetree/bindings/pinctrl/rockchip,pinctrl.txt#L40


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:
 


-- 
Best Regards,
Chanwoo Choi
Samsung Electronics