Re: [PATCH] clk: bcm: Add driver for Northstar ILP clock

On 29 July 2016 at 15:15, Mark Rutland [off-list ref] wrote:

On Fri, Jul 29, 2016 at 02:58:32PM +0200, Rafał Miłecki wrote:

quoted

From: Rafał Miłecki <rafal@milecki.pl>

This clock is present on cheaper Northstar devices like BCM53573 or
BCM47189 using Corex-A7. This driver uses PMU (Power Management Unit)
to calculate clock rate and allows using it in a generic (clk_*) way.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
---
 .../devicetree/bindings/clock/brcm,ns-ilp.txt      |  28 ++++
 drivers/clk/bcm/Makefile                           |   1 +
 drivers/clk/bcm/clk-ns-ilp.c                       | 146 +++++++++++++++++++++
 3 files changed, 175 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/brcm,ns-ilp.txt
 create mode 100644 drivers/clk/bcm/clk-ns-ilp.c

diff --git a/Documentation/devicetree/bindings/clock/brcm,ns-ilp.txt b/Documentation/devicetree/bindings/clock/brcm,ns-ilp.txt
new file mode 100644
index 0000000..c4df38e
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/brcm,ns-ilp.txt

@@ -0,0 +1,28 @@
+Broadcom Northstar ILP clock
+============================
+
+This binding uses the common clock binding:
+    Documentation/devicetree/bindings/clock/clock-bindings.txt
+
+This binding is used for ILP clock on Broadcom Northstar devices using
+Corex-A7 CPU. ILP clock depends on ALP one and has to be calculated on
+runtime.
+
+Required properties:
+- compatible: "brcm,ns-ilp"
+- reg: iomem address range of PMU (Power Management Unit)
+- reg-names: "pmu", the only needed & supported reg right now

From the commit message and binding description, it sounds like there
should be a binding for the PMU, and that should cover the clocks
required/exported by the PMU.

This is a bit of problem, because PMU handles a lot of different stuff
and is used by various drivers. Some examples of what you can do
with/find on a PMU:
1) Power management
2) Watchdog
3) Timer
4) XTAL
5) PLLs
6) Control registers for some ARM debugging (whatever it is), UART, JTAG, more

PMU is used by different drivers, e.g.:
1) Ethernet driver
2) Wireless driver
3) NAND controller driver

I don't have access to Broadcom's datasheets so unfortunately I can't
provide all details.

quoted

+- clocks: should reference an ALP clock
+- clock-names: "alp", the only needed & supported clock right now
+- #clock-cells: should be <0>

How many clocks does the PMU output, including the ILP clock?

Well, ALP clock (AKA XTAL clock) is definitely part of PMU. It's a
fixed rate clock with rate specific to the chip.

I think ILP is also part of PMU (again: I don't have datasheets) as
PMU has this ALP_PER_4ILP register.

From Broadcom's SDK I can say they also have "ARM debug unit" on some
chipsets. It requires enabling "ARM debug clk" to operate which is
handled by PMU as well.

-- 
Rafał