On 25/10/2021 18:12, Sam Protsenko wrote:

Some clocks must be registered before init calls. For example MCT clock
(from CMU_PERI) is needed for MCT timer driver, which is registered
with TIMER_OF_DECLARE(). By the time we get to core_initcall() used for
clk-exynos850 platform driver init, it's already too late. Inability to
get "mct" clock in MCT driver leads to kernel panic, as functions
registered with *_OF_DECLARE() can't do deferred calls. MCT timer driver
can't be fixed either, as it's acting as a clock source and it's
essential to register it in start_kernel() -> time_init().

Let's register CMU_PERI clocks early, using CLK_OF_DECLARE_DRIVER(), and
do all stuff relying on "struct dev" object (like runtime PM and
enabling bus clock) later in platform driver probe. Basically
CLK_OF_DECLARE_DRIVER() matches CMU compatible, but clears OF_POPULATED
flag, which allows the same device to be matched again later.

Similar issue was discussed at [1] and addressed in commit 1f7db7bbf031
("clk: renesas: cpg-mssr: Add early clock support"), as well as in
drivers/clk/mediatek/clk-mt2712.c.

[1] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20180829132954.64862-2-chris.brandt@renesas.com/

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
---
Changes in v2:
  - Register only CMU_PERI clocks early

Notes:
  - This patch should be applied on top of CMU_APM series
    (clk: samsung: exynos850: Implement CMU_APM domain)

 drivers/clk/samsung/clk-exynos850.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

Reviewed-by: Krzysztof Kozlowski <redacted>


Best regards,
Krzysztof