Am 2023-06-16 10:55, 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>
Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
---
.../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..10a6df752f6f 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.
+ broken-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 then status register permanently
becomes
+ read-only as the SRWD bit cannot be reset. This boolean flag can
be used
+ on systems in which WP signal is not connected, to avoid setting
the SRWD
+ bit while writing the status register.
This is not true for all flashes, for example, Macronix flashes seem to
have
an internal pull-up, so if the pin is unconnected H/W write protection
is
disabled.
So maybe only mention that "if the pin is wrongly tied to GND (that
includes
internal pull-downs) or it is left floating".
Same goes for your comment in the driver code. Sorry for nitpicking, but
I fear some misuse of this property to disable the locking of the status
register.
If the WP signal is hard strapped
+ to LOW then it is not broken as it can be a valid use case.
+
I'm not sure it the bindings use negative notion of pins, because that
signal is usually called WP#.
-michael
