From: Stephen Boyd <sboyd@kernel.org>
Date: Fri, 15 Oct 2021 14:55:47 -0700

Quoting Pali Rohár (2021-10-15 02:37:01)

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On Friday 15 October 2021 11:09:37 Pali Rohár wrote:

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On Thursday 14 October 2021 17:13:03 Stephen Boyd wrote:

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Quoting Pali Rohár (2021-09-30 02:58:35)

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diff --git a/Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml b/Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml
new file mode 100644
index 000000000000..175f5c8f2bc5
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/marvell,armada-3700-uart-clock.yaml

@@ -0,0 +1,59 @@

[..]

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+  '#clock-cells':
+    const: 1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - '#clock-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    uartclk: clock-controller@12010 {

The uart device is at 0x12000 and the clock-controller is at 0x12010?
This looks like a node is being put into DT to represent a clk driver.
Why can't we register a clk from the uart device driver itself? I think
we talked about this a month or two ago but it still isn't clear to me.

We have already talked about it and I have already wrote reasons. UART
clk is shared for both UART1 and UART2. And UART clk regs are in both
address spaces of UART1 and UART2. UART1 or UART2 can be independently
disabled on particular board (as pins are MPP which may be configured to
different function). So you have a board only with UART2, you have to
disable UART1 node, but at the same time you have to access UART clk to
drive UART2. And UART clk bits are in UART1 address space.

It is explained also in commit message of patch 2/6.

Cool, thanks for the pointer.

Why are the two uarts split into different device nodes? It looks like
it's one device that was split into two nodes because they're fairly
similar hardware blocks, and one or the other may not be used on the
board so we want to use status = "disabled" to indicate that. Sadly the
hardware team has delivered them as a single package into the SoC at
address 0x12000 and then stuck a common clk for both uarts into the same
uart wrapper. Here's a clk, job done!

Is it a problem to map UART1 address space when it isn't used on the
board? I'm trying to understand why it can't work to register two uart
ports from one device node and driver.

Separate nodes are needed because stdin-path and stdout-patch need to
be able to point at a specific device node.