summaryrefslogtreecommitdiffstats
path: root/Documentation/arm/sunxi
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/arm/sunxi
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/arm/sunxi')
-rw-r--r--Documentation/arm/sunxi/clocks.rst57
1 files changed, 57 insertions, 0 deletions
diff --git a/Documentation/arm/sunxi/clocks.rst b/Documentation/arm/sunxi/clocks.rst
new file mode 100644
index 000000000..23bd03f3e
--- /dev/null
+++ b/Documentation/arm/sunxi/clocks.rst
@@ -0,0 +1,57 @@
+=======================================================
+Frequently asked questions about the sunxi clock system
+=======================================================
+
+This document contains useful bits of information that people tend to ask
+about the sunxi clock system, as well as accompanying ASCII art when adequate.
+
+Q: Why is the main 24MHz oscillator gatable? Wouldn't that break the
+ system?
+
+A: The 24MHz oscillator allows gating to save power. Indeed, if gated
+ carelessly the system would stop functioning, but with the right
+ steps, one can gate it and keep the system running. Consider this
+ simplified suspend example:
+
+ While the system is operational, you would see something like::
+
+ 24MHz 32kHz
+ |
+ PLL1
+ \
+ \_ CPU Mux
+ |
+ [CPU]
+
+ When you are about to suspend, you switch the CPU Mux to the 32kHz
+ oscillator::
+
+ 24Mhz 32kHz
+ | |
+ PLL1 |
+ /
+ CPU Mux _/
+ |
+ [CPU]
+
+ Finally you can gate the main oscillator::
+
+ 32kHz
+ |
+ |
+ /
+ CPU Mux _/
+ |
+ [CPU]
+
+Q: Were can I learn more about the sunxi clocks?
+
+A: The linux-sunxi wiki contains a page documenting the clock registers,
+ you can find it at
+
+ http://linux-sunxi.org/A10/CCM
+
+ The authoritative source for information at this time is the ccmu driver
+ released by Allwinner, you can find it at
+
+ https://github.com/linux-sunxi/linux-sunxi/tree/sunxi-3.0/arch/arm/mach-sun4i/clock/ccmu