On 2/3/21 3:23 PM, Rob Herring wrote:

On Tue, Feb 2, 2021 at 6:01 PM Sean Anderson [off-list ref] wrote:

quoted

On 2/2/21 2:02 PM, Rob Herring wrote:

quoted

On Tue, Feb 2, 2021 at 4:36 AM Damien Le Moal [off-list ref] wrote:

quoted

The sifive gpio IP block supports up to 32 GPIOs. Reflect that in the
interrupts property description and maxItems. Also add the standard
ngpios property to describe the number of GPIOs available on the
implementation.

Also add the "canaan,k210-gpiohs" compatible string to indicate the use
of this gpio controller in the Canaan Kendryte K210 SoC. If this
compatible string is used, do not define the clocks property as
required as the K210 SoC does not have a software controllable clock
for the Sifive gpio IP block.

Cc: Paul Walmsley <redacted>
Cc: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Damien Le Moal <redacted>
---
   .../devicetree/bindings/gpio/sifive,gpio.yaml | 21 ++++++++++++++++---
   1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/gpio/sifive,gpio.yaml b/Documentation/devicetree/bindings/gpio/sifive,gpio.yaml
index ab22056f8b44..2cef18ca737c 100644
--- a/Documentation/devicetree/bindings/gpio/sifive,gpio.yaml
+++ b/Documentation/devicetree/bindings/gpio/sifive,gpio.yaml

@@ -16,6 +16,7 @@ properties:
         - enum:
             - sifive,fu540-c000-gpio
             - sifive,fu740-c000-gpio
+          - canaan,k210-gpiohs
         - const: sifive,gpio0

     reg:

@@ -23,9 +24,9 @@ properties:

     interrupts:
       description:
-      interrupt mapping one per GPIO. Maximum 16 GPIOs.
+      interrupt mapping one per GPIO. Maximum 32 GPIOs.
       minItems: 1
-    maxItems: 16
+    maxItems: 32

     interrupt-controller: true

@@ -38,6 +39,10 @@ properties:
     "#gpio-cells":
       const: 2

+  ngpios:
+    minimum: 1
+    maximum: 32

What's the default as obviously drivers already assume something.

The driver currently assumes 16. However, as noted in reply to Atish,
the number of GPIOs is configurable.

So you need a 'default: 16' here.

There is no reasonable default. This device can be configured to have
any number of GPIOs between 1 and 32.

quoted

quoted

Does a driver actually need to know this? For example, does the
register stride change or something?

No. I believe that the number of GPIOs sets which bits in the control
registers are valid. So the maximum number of GPIOs is the word width of
the bus.

So like register access size (e.g. readw vs readl)? If so, we have
'reg-io-width' for that purpose.

This is just the "maximum configurable" due to how the device's
registers are laid out. If you wanted to have more GPIOs than the
register access size, you would need to make more extensive (and likely
incompatible) modifications to the device. However, I don't believe
there are any devices with 64-bit register width (yet) and the driver
does not support 64-bit accesses.

quoted

quoted

Please don't add it if the only purpose is error check your DT (IOW,
if it just checks the max cell value in gpios phandles).

Why not? This seems like exactly the situation this property was
designed for.

Because it is redundant. All the GPIO lines you want to use should be
connected to something with a *-gpios property. If not, then that's a
failure to describe part of the h/w.

This is wrong. On SoCs with pinmuxing (such as this one), not all GPIO
lines may be connected for any particular board.

For comparison, we generally don't define how many interrupts an
interrupt controller has. Or how many power-domains a power domain
provider has. I can go on with every provider/consumer binding...

And yet the in-kernel documentation *specifically* recommends using this
property in this situation. I suggest you submit a patch to remove that
paragraph if you think that it is not necessary.

--Sean