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Whenever pclk_vo is enabled hclk_vo must be enabled as well. This is described in the Reference Manual as: | 2.8.6 NIU Clock gating reliance | | A part of niu clocks have a dependence on another niu clock in order to | sharing the internal bus. When these clocks are in use, another niu | clock must be opened, and cannot be gated. These clocks and the special | clock on which they are relied are as following: | | Clocks which have dependency The clock which can not be gated | ----------------------------------------------------------------- | ... | pclk_vo_niu, hclk_vo_s_niu hclk_vo_niu | ... The clock framework doesn't offer a way to enable clock B whenever clock A is enabled, at least not when B is not an ancestor of A. Workaround this by marking hclk_vo as critical so it is never disabled. This is suboptimal in terms of power consumption, but a stop gap solution until the clock framework has a way to deal with this. We have this clock tree: | aclk_vo 2 2 0 300000000 0 0 50000 Y | aclk_hdcp 0 0 0 300000000 0 0 50000 N | pclk_vo 2 3 0 75000000 0 0 50000 Y | pclk_edp_ctrl 0 0 0 75000000 0 0 50000 N | pclk_dsitx_1 0 0 0 75000000 0 0 50000 N | pclk_dsitx_0 1 2 0 75000000 0 0 50000 Y | pclk_hdmi_host 1 2 0 75000000 0 0 50000 Y | pclk_hdcp 0 0 0 75000000 0 0 50000 N | hclk_vo 2 5 0 150000000 0 0 50000 Y | hclk_hdcp 0 0 0 150000000 0 0 50000 N | hclk_vop 0 2 0 150000000 0 0 50000 N Without this patch the edp, dsitx, hdmi and hdcp driver would enable their clocks which then enables pclk_vo, but hclk_vo stays disabled and register accesses just hang. hclk_vo is enabled by the VOP2 driver, so reproducibility of this issue depends on the probe order. Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de> Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Reviewed-by: Robin Murphy <robin.murphy@arm.com> Tested-by: Michael Riesch <michael.riesch@wolfvision.net> Link: https://lore.kernel.org/r/20220422072841.2206452-2-s.hauer@pengutronix.de Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.