Re: [PATCH v2 RESEND 1/5] dt-bindings: soc: samsung: Add Exynos USI bindings

On Fri, Dec 3, 2021 at 1:36 PM Sam Protsenko [off-list ref] wrote:

On Tue, 30 Nov 2021 at 21:31, Rob Herring [off-list ref] wrote:

quoted

On Tue, Nov 30, 2021 at 01:13:21PM +0200, Sam Protsenko wrote:

quoted

Add constants for choosing USIv2 configuration mode in device tree.
Those are further used in USI driver to figure out which value to write
into SW_CONF register. Also document USIv2 IP-core bindings.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
---
Changes in v2:
  - Combined dt-bindings doc and dt-bindings header patches
  - Added i2c node to example in bindings doc
  - Added mentioning of shared internal circuits
  - Added USI_V2_NONE value to bindings header

 .../bindings/soc/samsung/exynos-usi.yaml      | 135 ++++++++++++++++++
 include/dt-bindings/soc/samsung,exynos-usi.h  |  17 +++
 2 files changed, 152 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/soc/samsung/exynos-usi.yaml
 create mode 100644 include/dt-bindings/soc/samsung,exynos-usi.h

diff --git a/Documentation/devicetree/bindings/soc/samsung/exynos-usi.yaml b/Documentation/devicetree/bindings/soc/samsung/exynos-usi.yaml
new file mode 100644
index 000000000000..a822bc62b3cd
--- /dev/null
+++ b/Documentation/devicetree/bindings/soc/samsung/exynos-usi.yaml

@@ -0,0 +1,135 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/soc/samsung/exynos-usi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Samsung's Exynos USI (Universal Serial Interface) binding
+
+maintainers:
+  - Sam Protsenko <semen.protsenko@linaro.org>
+  - Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
+
+description: |
+  USI IP-core provides selectable serial protocol (UART, SPI or High-Speed I2C).
+  USI shares almost all internal circuits within each protocol, so only one
+  protocol can be chosen at a time. USI is modeled as a node with zero or more
+  child nodes, each representing a serial sub-node device. The mode setting
+  selects which particular function will be used.
+
+  Refer to next bindings documentation for information on protocol subnodes that
+  can exist under USI node:
+
+  [1] Documentation/devicetree/bindings/serial/samsung_uart.yaml
+  [2] Documentation/devicetree/bindings/i2c/i2c-exynos5.txt
+  [3] Documentation/devicetree/bindings/spi/spi-samsung.txt
+
+properties:
+  $nodename:
+    pattern: "^usi@[0-9a-f]+$"
+
+  compatible:
+    const: samsung,exynos-usi-v2

Use SoC based compatibles.

In this particular case, I'd really prefer to have it like this. Most
likely we'll only have USIv1 and USIv1 in the end, and I think that
would be more clear to have USI version in compatible, rather than SoC
name. Please let me know if you have a strong opinion on this one --
if so I'll re-send.

Fine if you have some evidence the ratio of versions to SoC are much
more than 1:1 and the versions correspond to something (IOW, you
aren't making them up).

We went down the version # path with QCom and in the end about every
SoC had a different version.

quoted

quoted

+
+  reg:
+    maxItems: 1
+
+  clocks:
+    items:
+      - description: Bus (APB) clock
+      - description: Operating clock for UART/SPI/I2C protocol
+
+  clock-names:
+    items:
+      - const: pclk
+      - const: ipclk
+
+  ranges: true
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 1
+
+  samsung,sysreg:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    description:
+      Should be phandle/offset pair. The phandle to System Register syscon node
+      (for the same domain where this USI controller resides) and the offset
+      of SW_CONF register for this USI controller.
+
+  samsung,mode:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Selects USI function (which serial protocol to use). Refer to
+      <include/dt-bindings/soc/samsung,exynos-usi.h> for valid USI mode values.

This seems to be redundant. Just check which child is enabled.

I think it's not that easy. Soon we'll have USIv1 support added, and
that has some weird configurations, like having dual I2C mode (two
child I2C nodes must be enabled) and UART+I2C mode, etc.

So you are going to turn around and make this an array? If you already
know you have changes, I'd rather review this all at once.

Looks like it
might take some not very elegant logic to figure out which exactly
mode value should be written in SW_CONF register in that way, it's
much easier to just specify mode in USI node. Also, that reflects
hardware better: we actually write that specified mode to SW_CONF
register.

You just have to compare the child node names or compatibles.

Also, later we might want to be able to switch that mode via
SysFS, e.g. for testing purposes. Current design seems to be better
suited for some things like that.

The binding should have no impact on that. If for testing, use debugfs.

Please let me know if you have a strong opinion on this one, or it's
ok to leave it as is.

All other comments are addressed and will be present in v3. Thanks for
the review!