Re: [PATCH v7 05/15] dt-bindings: Document the STM32 reset bindings
From: Daniel Thompson
Date: Tue May 05 2015 - 10:08:07 EST
On 04/05/15 12:25, Maxime Coquelin wrote:
2015-05-02 12:01 GMT+02:00 Daniel Thompson <daniel.thompson@xxxxxxxxxx>:
On 02/05/15 08:55, Maxime Coquelin wrote:
2015-05-01 10:08 GMT+02:00 Daniel Thompson <daniel.thompson@xxxxxxxxxx>:
On 30/04/15 17:20, Maxime Coquelin wrote:
This adds documentation of device tree bindings for the
STM32 reset controller.
Tested-by: Chanwoo Choi <cw00.choi@xxxxxxxxxxx>
Acked-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
Acked-by: Rob Herring <robh@xxxxxxxxxx>
Signed-off-by: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
---
.../devicetree/bindings/reset/st,stm32-rcc.txt | 107
+++++++++++++++++++++
1 file changed, 107 insertions(+)
create mode 100644
Documentation/devicetree/bindings/reset/st,stm32-rcc.txt
diff --git a/Documentation/devicetree/bindings/reset/st,stm32-rcc.txt
b/Documentation/devicetree/bindings/reset/st,stm32-rcc.txt
new file mode 100644
index 0000000..c1b0f8d
--- /dev/null
+++ b/Documentation/devicetree/bindings/reset/st,stm32-rcc.txt
@@ -0,0 +1,107 @@
+STMicroelectronics STM32 Peripheral Reset Controller
+====================================================
+
+The RCC IP is both a reset and a clock controller. This documentation
only
+documents the reset part.
+
+Please also refer to reset.txt in this directory for common reset
+controller binding usage.
+
+Required properties:
+- compatible: Should be "st,stm32-rcc"
+- reg: should be register base and length as documented in the
+ datasheet
+- #reset-cells: 1, see below
+
+example:
+
+rcc: reset@40023800 {
+ #reset-cells = <1>;
+ compatible = "st,stm32-rcc";
Do you intend the clock driver to use the same compatible string (given
it
is the same bit of hardware).
If so, is it better to use st,stm32f4-rcc here? It seems unlikey to me
that
the register layout of the PLLs and dividers can be the same on the f7
parts
(and later).
I agree we need a compatible dedicate to f4 series for clocks, and
maybe even one for f429 (to be checked).
For the reset part, we don't have this need.
So either we use only "st,stm32f4" as you suggest, or we can have both
in device tree:
rcc: reset@40023800 {
#reset-cells = <1>;
compatible = "st,stm32f4-rcc", "st,stm32-rcc";
reg = <0x40023800 0x400>;
};
What do you think?
Having both makes sense. The reset driver probably doesn't care about
differences between F4 and F7 (I know very little about F7 but I can't think
of any obvious h/ware evolution that would confuse the current reset
driver).
+ reg = <0x40023800 0x400>;
+};
+
+Specifying softreset control of devices
+=======================================
+
+Device nodes should specify the reset channel required in their
"resets"
+property, containing a phandle to the reset device node and an index
specifying
+which channel to use.
+The index is the bit number within the RCC registers bank, starting
from
RCC
+base address.
+It is calculated as: index = register_offset / 4 * 32 + bit_offset.
+Where bit_offset is the bit offset within the register.
+For example, for CRC reset:
+ crc = AHB1RSTR_offset / 4 * 32 + CRCRST_bit_offset = 0x10 / 4 * 32 +
12
= 140
+
+example:
+
+ timer2 {
+ resets = <&rcc 256>;
+ };
+
+List of valid indices for STM32F429:
+ - gpioa: 128
+ - gpiob: 129
...
<snip>
...
+ - sai1: 310
+ - ltdc: 314
These numbers are stable for all STM32F4 family parts. Should this table
go
into a dt-bindings header file?
This has already been discussed with Philipp and Arnd in earlier
versions of this series [0].
I initially created a header file, and we decided going this way finally.
Thanks for the link. I had overlooked that (I only really started paying
attention at v5; I should probably have looked further back before
commenting).
However...
Arnd's concerns about mergability of headers can also be met by using h/ware
values in the header file can't there. To be honest my comment was pretty
heavily influenced after having read a recent patch from Rob Herring (
https://lkml.org/lkml/2015/5/1/14 ) which does exactly this.
The main reason I got interested in having a header is that the reset bits
and the clock gate bits are encoded using the same bit patterns so I
wondering it we could express that only once.
Ok, I understand your need, and it makes sense.
The problem is that the values defined today cannot be re-used
directly for clocks.
Since the calculation is starting from rcc base, there is a 128 offset.
To re-use the same values, maybe we should create a mfd dt-binding header file.
It would contain the bits definition starting from 0, and define
macros for both reset and clocks to add the offsets.
For example, includes/dt-bindings/mfd/stm32f4-rcc.h would look like:
#define GPIOA 0
#define GPIOB 1
...
#define LTDC 186
#define STM32F4_RESET(x) (x + 128)
#define STM32F4_CLOCK(x) (x + 384)
Then, in DT, a reset would be described like this:
timer2 {
resets = <&rcc STM32F4_RESET(TIM2)>;
};
Phillip, Daniel, does that look acceptable to you?
Doesn't look unreasonable.
I am a little uneasy simply because there are very few similar header
files in that directory but I haven't thought of a better idea.
Daniel.
Kind regards,
Maxime
I guess it doesn't matter that much, especially given there is only one
.dtsi file, and we can add a header later and remain binary compatible.
However if the same number set does end up repeated in different .dtsi files
I think that would motivate adding a header for F4 family.
Daniel.
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