diff mbox series

[v2,3/4] dt-bindings: i2c-stm32: add SMBus Alert bindings

Message ID 1593070769-9106-4-git-send-email-alain.volmat@st.com
State Changes Requested
Headers show
Series stm32-f7: Addition of SMBus Alert / Host-notify features | expand

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Commit Message

Alain Volmat June 25, 2020, 7:39 a.m. UTC
Add a new binding of the i2c-stm32f7 driver to enable the handling
of the SMBUS-Alert.

The I2C/SMBUS framework already provides a mechanism to enable SMBus-Alert
by naming an IRQ line "smbus_alert". However, on stm32, the SMBus-Alert is
part of the i2c IRQ. Using the smbus_alert naming here would lead to having
2 handlers (the handler of the driver and the smbus_alert handler
from I2C/SMBUS framework) on the unique i2c IRQ of the stm32. Meaning that
the smbus_alert handler would get called for all IRQ generated by the stm32
I2C controller.

For that reason, the smbus_alert IRQ naming cannot be used and a dedicated
binding is introduced.

Signed-off-by: Alain Volmat <alain.volmat@st.com>
---
v2: Clarify commit message

 Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Wolfram Sang June 30, 2020, 7:41 p.m. UTC | #1
On Thu, Jun 25, 2020 at 09:39:28AM +0200, Alain Volmat wrote:
> Add a new binding of the i2c-stm32f7 driver to enable the handling
> of the SMBUS-Alert.
> 
> The I2C/SMBUS framework already provides a mechanism to enable SMBus-Alert
> by naming an IRQ line "smbus_alert". However, on stm32, the SMBus-Alert is
> part of the i2c IRQ. Using the smbus_alert naming here would lead to having
> 2 handlers (the handler of the driver and the smbus_alert handler
> from I2C/SMBUS framework) on the unique i2c IRQ of the stm32. Meaning that
> the smbus_alert handler would get called for all IRQ generated by the stm32
> I2C controller.
> 
> For that reason, the smbus_alert IRQ naming cannot be used and a dedicated
> binding is introduced.

What if we update the core to not register another irq handler if the
"smbus_alert" and main irq are the same?

I think it could work. However, while trying to make a proof-of-concept,
I found that irq descriptions in the generic i2c binding document are
probably mixed up. And before fixing that, I'd like to get HostNotify
done first.

Makes sense?
Rob Herring July 14, 2020, 2:30 a.m. UTC | #2
On Tue, Jun 30, 2020 at 09:41:07PM +0200, Wolfram Sang wrote:
> On Thu, Jun 25, 2020 at 09:39:28AM +0200, Alain Volmat wrote:
> > Add a new binding of the i2c-stm32f7 driver to enable the handling
> > of the SMBUS-Alert.
> > 
> > The I2C/SMBUS framework already provides a mechanism to enable SMBus-Alert
> > by naming an IRQ line "smbus_alert". However, on stm32, the SMBus-Alert is
> > part of the i2c IRQ. Using the smbus_alert naming here would lead to having
> > 2 handlers (the handler of the driver and the smbus_alert handler
> > from I2C/SMBUS framework) on the unique i2c IRQ of the stm32. Meaning that
> > the smbus_alert handler would get called for all IRQ generated by the stm32
> > I2C controller.
> > 
> > For that reason, the smbus_alert IRQ naming cannot be used and a dedicated
> > binding is introduced.
> 
> What if we update the core to not register another irq handler if the
> "smbus_alert" and main irq are the same?
> 
> I think it could work. However, while trying to make a proof-of-concept,
> I found that irq descriptions in the generic i2c binding document are
> probably mixed up. And before fixing that, I'd like to get HostNotify
> done first.

Why does this even need to be in DT? Can't the driver just register that 
it supports SMBus alert or have some call to the core signaling an SMBus 
alert? 

Rob
Wolfram Sang July 21, 2020, 6:22 a.m. UTC | #3
Hi Rob,

> > > The I2C/SMBUS framework already provides a mechanism to enable SMBus-Alert
> > > by naming an IRQ line "smbus_alert". However, on stm32, the SMBus-Alert is
> > > part of the i2c IRQ. Using the smbus_alert naming here would lead to having
> > > 2 handlers (the handler of the driver and the smbus_alert handler
> > > from I2C/SMBUS framework) on the unique i2c IRQ of the stm32. Meaning that
> > > the smbus_alert handler would get called for all IRQ generated by the stm32
> > > I2C controller.
> > > 
> > > For that reason, the smbus_alert IRQ naming cannot be used and a dedicated
> > > binding is introduced.
> > 
> > What if we update the core to not register another irq handler if the
> > "smbus_alert" and main irq are the same?
> > 
> > I think it could work. However, while trying to make a proof-of-concept,
> > I found that irq descriptions in the generic i2c binding document are
> > probably mixed up. And before fixing that, I'd like to get HostNotify
> > done first.
> 
> Why does this even need to be in DT? Can't the driver just register that 
> it supports SMBus alert or have some call to the core signaling an SMBus 
> alert? 

If we emulate this SMBus behaviour with I2C, it means we apply
additional restrictions. In this case, there is an address which can't
be used anymore. Because there is another case of additional
restrictions, I proposed the binding "smbus" which means this bus is not
I2C but SMBus, so it is more restricted.

Thanks,

   Wolfram
diff mbox series

Patch

diff --git a/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml b/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml
index f2fcbb361180..6fde046fae5e 100644
--- a/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml
+++ b/Documentation/devicetree/bindings/i2c/st,stm32-i2c.yaml
@@ -36,6 +36,10 @@  allOf:
             minItems: 3
             maxItems: 3
 
+        st,smbus-alert:
+          description: Enable the SMBus Alert feature
+          $ref: /schemas/types.yaml#/definitions/flag
+
   - if:
       properties:
         compatible: