[PATCH v5 4/5] dt: bindings: i2c-mux-pca954x: Add documentation for nxp,irq-mask-enable

[Phil Reid <preid-qgqNFa1JUf/o2iN0hyhwsIdd74u8MsAO@public.gmane.org>]

Unfortunately some hardware device will assert their irq line immediately
on power on and provide no mechanism to mask the irq. As the i2c muxes
provide no method to mask irq line this provides a work around by keeping
the parent irq masked until enough device drivers have loaded to service
all pending interrupts.

For example the the ltc1760 assert its SMBALERT irq immediately on power
on. With two ltc1760 attached to bus 0 & 1 on a pca954x mux when the first
device is registered irq are enabled and fire continuously as the second
device driver has not yet loaded. Setting this parameter to <1 1> will
delay the irq being enabled until both devices are ready.

Signed-off-by: Phil Reid <preid-qgqNFa1JUf/o2iN0hyhwsIdd74u8MsAO@public.gmane.org>
---
 Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
index aa09704..ac71be6 100644
--- a/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c-mux-pca954x.txt
@@ -19,6 +19,8 @@ Optional Properties:
   - i2c-mux-idle-disconnect: Boolean; if defined, forces mux to disconnect all
     children in idle state. This is necessary for example, if there are several
     multiplexers on the bus and the devices behind them use same I2C addresses.
+  - nxp,irq-mask-enable: array; Defines the minimum number of chips that must
+    register an irq for each channel before the parent irq line in enabled.
   - interrupt-parent: Phandle for the interrupt controller that services
     interrupts for this device.
   - interrupts: Interrupt mapping for IRQ.
@@ -36,6 +38,7 @@ Example:
 		#size-cells = <0>;
 		reg = <0x74>;
 
+		nxp,irq-mask-enable = <0 0 0 0 1 0 0 0>;
 		interrupt-parent = <&ipic>;
 		interrupts = <17 IRQ_TYPE_LEVEL_LOW>;
 		interrupt-controller;
-- 
1.8.3.1

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