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([2a01:e34:ed2f:f020:5ebd:8bd9:d549:4211]) by smtp.googlemail.com with ESMTPSA id u18sm15538371wmj.15.2021.06.21.03.24.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jun 2021 03:24:45 -0700 (PDT) Subject: Re: [PATCH 1/2] clocksource/drivers/exynos_mct: Prioritise Arm arch timer on arm64 To: Marek Szyprowski , Will Deacon , Chanwoo Choi Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Krzysztof Kozlowski , Krzysztof Kozlowski , Thomas Gleixner References: <20210608154341.10794-1-will@kernel.org> <20210608154341.10794-2-will@kernel.org> <466bfc19-2260-87c6-c458-b43cf23617e3@samsung.com> <2a0181ea-a26e-65e9-16f6-cc233b6b296f@linaro.org> <20210617214748.GC25403@willie-the-truck> <95fb8ea3-f409-55ee-6b5c-f19858dd0fab@samsung.com> From: Daniel Lezcano Message-ID: <6847bb2f-02ac-35a4-bb7a-491a52325a60@linaro.org> Date: Mon, 21 Jun 2021 12:24:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <95fb8ea3-f409-55ee-6b5c-f19858dd0fab@samsung.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21/06/2021 12:17, Marek Szyprowski wrote: [ ... ] >>>>>> I'm not sure that exynos mct is working without problem >>>>>> such as the case of 6282edb72bed. >>>>>> As described on On ,6282edb72bed the arch timer on exynos SoC >>>>>> depends on Exynos MCT device. the arch timer is not able to work >>>>>> without Exynos MCT because of using the common module. >>>>> Is it possible to change the DT to have a phandle to the exynos_mct, so >>>>> it will be probed before the arch_arm_timer ? >>>> I think that DT changes is not proper way to keep the order between >>>> exynos_mct and arch timer. >>> exynos4_mct_frc_start() is called unconditionally from probe via >>> exynos4_clocksource_init() so as long as the mct probes first, then the >>> arch timer should work, no? The rating shouldn't affect that. >> How do you ensure the exynos mct is probed before the arch timer ? >> >> The Makefile provides the right order, but the dependency is implicit. > > In my test systems based on Exynos5433, the bootloader enabled MCT, so > kernel can also start with arch_timer then switch to MCT. The probe > order also depend on the order of DT nodes, so with the current dts MCT > is probed first. This is not the best approach, but so far it works. Right, generally assuming the firmware is doing the right thing from an initialization POV is not a good idea :/ But in our case, as pointed by Will, the cpuhotplug ordering gives the right sequence. So it should be fine. -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog