Am 2023-06-15 13:16, schrieb Amit Kumar Mahapatra:
If the WP signal of the flash device is not connected and the software
sets
the status register write disable (SRWD) bit in the status register
then
thestatus register permanently becomes read-only. To avoid this added a
new
boolean DT property "broken-wp". If WP signal is not connected, then
this
property should be set in the DT to avoid setting the SRWD during
status
register write operation.
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xxxxxxx>
---
.../devicetree/bindings/mtd/jedec,spi-nor.yaml | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
index 89959e5c47ba..a509d34f14b2 100644
--- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
+++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
@@ -70,6 +70,19 @@ properties:
be used on such systems, to denote the absence of a reliable
reset
mechanism.
+ broken-wp:
+ type: boolean
+ description:
+ The 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 driven 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. But
+ if the WP signal of the flash device is not connected then
status register
+ permanently becomes read-only as the SRWD bit cannot be reset.
This boolean
+ flag can be used on such systems in which WP signal is not
connected, to
+ avoid setting the SRWD bit while writing the status register.
FWIW, this is also a valid use case: have the WP# pin tied to low, the
OEM will program the flash and then enable locking making the flash
permanently write protected. IWO, if the pin is hard strapped to low,
it is not always broken. You might add that to the description.
-michael
