linux-kernel - Re: [PATCH v2 6/9] clk: samsung: exynos850: Implement CMU

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Date:   Fri, 12 Aug 2022 12:54:15 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sam Protsenko <semen.protsenko@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Chanho Park <chanho61.park@...sung.com>,
        David Virag <virag.david003@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Tomasz Figa <tomasz.figa@...il.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH v2 6/9] clk: samsung: exynos850: Implement CMU_IS domain

On 09/08/2022 14:33, Sam Protsenko wrote:
> CMU_IS clock domain provides clocks for IS IP-core (Image Signal
> Processing Subsystem). According to Exynos850 TRM, CMU_IS generates
> CSIS, IPP, ITP, VRA and GDC clocks for BLK_IS.
> 
> This patch adds next clocks:
>   - bus clocks in CMU_TOP needed for CMU_IS
>   - all internal CMU_IS clocks
>   - leaf clocks for IS IP-core, CSIS (Camera Serial Interface Slave),
>     D_TZPC (TrustZone Protection Controller), CSIS DMA, GDC (Geometric
>     Distortion Correction), IPP (Image Preprocessing Processing core),
>     ITP (Image Texture Processing core), MCSC (Multi-Channel Scaler),
>     VRA (Visual Recognition Accelerator), PPMU (Platform Performance
>     Monitoring Unit), SysMMU and SysReg
> 
> IS related gate clocks in CMU_TOP were marked as CLK_IS_CRITICAL,
> because:
>   1. All of those have to be enabled in order to read
>      /sys/kernel/debug/clk/clk_summary file

This sounds exactly like previous ISP clock hangs:
https://lore.kernel.org/all/20171011092515.1698-1-m.szyprowski@samsung.com/

It looks like missing power domain references and your CLK_IS_CRITICAL
is not correct. These are not critical clocks.

>   2. When some user driver (e.g. exynos-sysmmu) disables some derived
>      leaf clock, it can lead to CMU_TOP clocks disable, which then makes
>      the system hang. To prevent that, the CLK_IS_CRITICAL flag is used,
>      as CLK_IGNORE_UNUSED is not enough.

These are not critical clocks and usage of CLK_IS_CRITICAL is not
appropriate. This looks like the same has as with other ISP, so it
should be handled in similar way.

Best regards,
Krzysztof