On Thu, Mar 18, 2021 at 02:44:48PM +0100, Alain Volmat wrote:

Based on the SMBus specification, SMBus Alert active state is low.
As often on SoC, the SMBus Alert pin is not only dedicated to this
feature and can also be used for another purpose (by configuring it
as alternate function for other functions via pinctrl).

"smbus" dt-binding has been introduced recently [1], however it is also
used to indicate usage of host-notify feature.
Relying on 'smbus' binding for SMBus-Alert as well as it was discussed
previously [2] would lead to requiring the SMBALERT# pin to be configured
as alternate function for i2c/smbus controller even if only host-notify is
needed.
Indeed, not doing so would lead to spurious SMBus Alert interrupts since
the i2c/smbus controller would see the (not configured) SMBA pin as low
level.

For that reason, SMBus-Alert needs to have its own binding in order
to only be enabled whenever SMBALERT# pin is configured as alternate
function for i2c/smbus controller.

[1] https://marc.info/?l=linux-i2c&m=159531254413805&w=2
[2] https://marc.info/?l=linux-renesas-soc&m=159361426409817&w=2

Please use lore.kernel.org links.

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>

---
v2: introduce st,smbus-alert property
---
 Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml | 5 +++++
 1 file changed, 5 insertions(+)

With that,

Reviewed-by: Rob Herring <robh@kernel.org>

Though I defer to Wolfram whether this could/should be common instead.

Rob