[PATCH v4 1/2] dt-bindings: mtd: jedec, spi-nor: Add DT property to avoid setting SRWD bit in status register

[Amit Kumar Mahapatra]

If the WP# signal of the flash device is either not connected or is wrongly
tied to GND (that includes internal pull-downs), and the software sets the
status register write disable (SRWD) bit in the status register then the
status register permanently becomes read-only. To avoid this added a new
boolean DT property "no-wp". If this property is set in the DT then the
software avoids setting the SRWD during status register write operation.

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra at amd.com>
Reviewed-by: Conor Dooley <conor.dooley at microchip.com>
Reviewed-by: Rob Herring <robh at kernel.org>
Reviewed-by: Michael Walle <michael at walle.cc>
---
 .../devicetree/bindings/mtd/jedec,spi-nor.yaml    | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
index 89959e5c47ba..97344969b02d 100644
--- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
+++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
@@ -70,6 +70,21 @@ properties:
       be used on such systems, to denote the absence of a reliable reset
       mechanism.
 
+  no-wp:
+    type: boolean
+    description:
+      The status register write disable (SRWD) bit in status register, combined
+      with the WP# signal, provides hardware data protection for the device. When
+      the SRWD bit is set to 1, and the WP# signal is either driven LOW or hard
+      strapped to LOW, the status register nonvolatile bits become read-only and
+      the WRITE STATUS REGISTER operation will not execute. The only way to exit
+      this hardware-protected mode is to drive WP# HIGH. If the WP# signal of the
+      flash device is not connected or is wrongly tied to GND (that includes internal
+      pull-downs) then status register permanently becomes read-only as the SRWD bit
+      cannot be reset. This boolean flag can be used on such systems to avoid setting
+      the SRWD bit while writing the status register. WP# signal hard strapped to GND
+      can be a valid use case.
+
   reset-gpios:
     description:
       A GPIO line connected to the RESET (active low) signal of the device.
-- 
2.17.1