This patchset adds some updates to clocks for Exynos4 platform and to the clock core. The patches are rebased on linux/next.
An interesting part might be 'propagation of clk_set_parent()'. This feature simplifies configuration of complex topologyof clocks by drivers. Such a situation happens for Exynos HDMI driver.
The HDMI device is clocked by sclk_hdmi clock. In older versions of SoC and its driver, the clock had two parent clocks: sclk_hdmiphy and sclk_pixel. The sclk_hdmi was a gated clock.
In the recent version of Exynos clock provider this topology was slightly changed. A new clock named mout_hdmi was introduced. This new clock represents the output of multiplexer that selects between sclk_hdmiphy and sclk_pixel.
After the change the sclk_hdmi is still gated but has a single parent - mout_hdmi.
This change caused interesting situation in Exynos HDMI driver because this driver used only sclk_hdmi. Now clk_set_parent(sclk_hdmi, ...) fails because sclk_hdmi has a single parent now. Using mout_hdmi instead of sclk_hdmi will not work because clk_enable(mout_hdmi) is not propagated to sclk_hdmi.
To solve this problem, the setup of mout_hdmi was added to Exynos HDMI in the patch: "drm/exynos: add mout_hdmi clock in hdmi driver to change parent"
IMO, this change breaks abstraction of clock API reveling too detailed information about clock topology to the driver.
Moreover, the driver no longer works with old DT bindings because they provide no mout_hdmi clock.
The clock set_parent propagation can be used to fix this. The clk_set_parent() is propagated to a parent as long as the current clock has a single parent and has the flag CLK_SET_PARENT_PARENT set.
Now Exynos HDMI can use only sclk_hdmi clock. The clk_enable() gates this clock directly and clk_set_parent() is propagated to mout_hdmi.
This new behaviour does not break DT bindings because mout_hdmi would be simply ignored.
After this change the 'add mout_hdmi clock' is no longer needed.
Regards, Tomasz Stanislawski
Tomasz Stanislawski (4): clk: propagate parent change up one level clk: exynos4: export sclk_hdmiphy clock clk: exynos4: enable clk_set_parent() propagation for sclk_hdmi and sclk_mixer clocks Revert "drm/exynos: add mout_hdmi clock in hdmi driver to change parent"
drivers/clk/clk.c | 6 ++++++ drivers/clk/samsung/clk-exynos4.c | 8 +++++--- drivers/gpu/drm/exynos/exynos_hdmi.c | 14 ++++---------- include/dt-bindings/clock/exynos4.h | 1 + include/linux/clk-provider.h | 1 + 5 files changed, 17 insertions(+), 13 deletions(-)