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7fa3708406
Some ARM64 Exynos chips are capable to control PLL clocks automatically.
For those chips, whether the PLL is controlled automatically or manually
is chosen in PLL_CON1 register with next bits:
[28] ENABLE_AUTOMATIC_CLKGATING
[1] MANUAL_PLL_CTRL
[0] AUTO_PLL_CTRL
The bl2 bootloader sets 0x10000001 value for some PLL_CON1 registers,
which means any attempt to control those PLLs manually (e.g.
disabling/enabling those PLLs or changing MUX parent clocks) would lead
to PLL lock timeout with error message like this:
Could not lock PLL ...
At the moment, all Samsung clock drivers implement manual clock control.
So in order to make it possible to control PLLs, corresponding PLL_CON1
registers should be set to 0x2 first.
Some older ARM64 chips don't implement the automatic clock control
though. It also might be desirable to configure some PLLs for manual
control, while keeping the default configuration for the rest. So it'd
convenient to choose this PLL mode for each CMU separately. Introduce
.manual_plls field to CMU structure to choose the PLL control mode.
Because it'll be initialized with "false" in all existing CMU
structures by default, it won't affect any existing clock drivers,
allowing for this feature to be enabled gradually when it's needed with
no change for the rest of users. In case .manual_plls is set, set
PLL_CON1 registers to manual control, akin to what's already done for
gate clocks in exynos_arm64_init_clocks(). Of course, PLL_CON1 registers
should be added to corresponding struct samsung_cmu_info::clk_regs array
to make sure they get initialized.
No functional change. This patch adds a feature, but doesn't enable it
for any users.
Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Link: https://lore.kernel.org/r/20240301015118.30072-1-semen.protsenko@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
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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 reStructuredText 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.