linux-kernel - Re: [PATCH] Revert "ARM: dts: exynos: Remove 'opp-shared' from Exynos4412 bus OPP-tables"

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Date:   Tue, 23 Feb 2021 10:24:41 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Markus Reichl <m.reichl@...etechno.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        최찬우 <cw00.choi@...sung.com>
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert
 "ARM: dts: exynos: Remove 'opp-shared' from Exynos4412 bus OPP-tables"

Hi Markus,

On 22.02.2021 10:54, Markus Reichl wrote:
> This reverts commit a23beead41a18c3be3ca409cb52f35bc02e601b9.
>
> I'm running an Odroid-X2 as headless 24/7 server.
> With plain stable 5.10.1 I had 54 up days without problems.
> With opp-shared removed on kernels before and now on 5.11
> my system freezes after some days on disk activity to eMMC
> (rsync, apt upgrade).
>
> The spontaneous hangs are not easy to reproduce but testing this
> for several months now I am quite confident that there is something
> wrong with this patch.
>
> Signed-off-by: Markus Reichl <m.reichl@...etechno.de>

Thanks for the report.

IMHO a straight revert is a bad idea. I would prefer to keep current opp 
definitions and disable the affected devfreq devices (probably right bus 
would be enough) or try to identify which transitions are responsible 
for that issue. I know that it would take some time to identify them, 
but that would be the best solution. Reverting leads to incorrect 
hardware description, what in turn confuses the driver and framework, 
what in turn hides a real problem.

Another problem related to devfreq on Exynos4412 has been introduced 
recently by the commit 86ad9a24f21e ("PM / devfreq: Add required OPPs 
support to passive governor"). You can see lots of the messages like 
this one:

devfreq soc:bus-acp: failed to update devfreq using passive governor

I didn't have time to check what's wrong there, but I consider devfreq 
on Exynos a little bit broken, so another solution would be just to 
disable it in the exynos_defconfig.

> ---
>   arch/arm/boot/dts/exynos4412.dtsi | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/arch/arm/boot/dts/exynos4412.dtsi b/arch/arm/boot/dts/exynos4412.dtsi
> index a142fe84010b..6246df278431 100644
> --- a/arch/arm/boot/dts/exynos4412.dtsi
> +++ b/arch/arm/boot/dts/exynos4412.dtsi
> @@ -405,6 +405,7 @@
>   
>   		bus_dmc_opp_table: opp-table1 {
>   			compatible = "operating-points-v2";
> +			opp-shared;
>   
>   			opp-100000000 {
>   				opp-hz = /bits/ 64 <100000000>;
> @@ -431,6 +432,7 @@
>   
>   		bus_acp_opp_table: opp-table2 {
>   			compatible = "operating-points-v2";
> +			opp-shared;
>   
>   			opp-100000000 {
>   				opp-hz = /bits/ 64 <100000000>;
> @@ -500,6 +502,7 @@
>   
>   		bus_leftbus_opp_table: opp-table3 {
>   			compatible = "operating-points-v2";
> +			opp-shared;
>   
>   			opp-100000000 {
>   				opp-hz = /bits/ 64 <100000000>;
> @@ -522,6 +525,7 @@
>   
>   		bus_display_opp_table: opp-table4 {
>   			compatible = "operating-points-v2";
> +			opp-shared;
>   
>   			opp-160000000 {
>   				opp-hz = /bits/ 64 <160000000>;
> @@ -533,6 +537,7 @@
>   
>   		bus_fsys_opp_table: opp-table5 {
>   			compatible = "operating-points-v2";
> +			opp-shared;
>   
>   			opp-100000000 {
>   				opp-hz = /bits/ 64 <100000000>;
> @@ -544,6 +549,7 @@
>   
>   		bus_peri_opp_table: opp-table6 {
>   			compatible = "operating-points-v2";
> +			opp-shared;
>   
>   			opp-50000000 {
>   				opp-hz = /bits/ 64 <50000000>;

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland