nvmem: core: Add support for keepout regions

Introduce support into the nvmem core for arrays of register ranges
that should not result in actual device access. For these regions a
constant byte (repeated) is returned instead on read, and writes are
quietly ignored and returned as successful.

This is useful for instance if certain efuse regions are protected
from access by Linux because they contain secret info to another part
of the system (like an integrated modem).

Signed-off-by: Evan Green <evgreen@chromium.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20201127102837.19366-3-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/nvmem-provider.h b/include/linux/nvmem-provider.h
index 06409a6c40bc..e162b757b6d5 100644
--- a/include/linux/nvmem-provider.h
+++ b/include/linux/nvmem-provider.h
@@ -31,6 +31,19 @@ enum nvmem_type {
 #define NVMEM_DEVID_AUTO	(-2)
 
 /**
+ * struct nvmem_keepout - NVMEM register keepout range.
+ *
+ * @start:	The first byte offset to avoid.
+ * @end:	One beyond the last byte offset to avoid.
+ * @value:	The byte to fill reads with for this region.
+ */
+struct nvmem_keepout {
+	unsigned int start;
+	unsigned int end;
+	unsigned char value;
+};
+
+/**
  * struct nvmem_config - NVMEM device configuration
  *
  * @dev:	Parent device.
@@ -39,6 +52,8 @@ enum nvmem_type {
  * @owner:	Pointer to exporter module. Used for refcounting.
  * @cells:	Optional array of pre-defined NVMEM cells.
  * @ncells:	Number of elements in cells.
+ * @keepout:	Optional array of keepout ranges (sorted ascending by start).
+ * @nkeepout:	Number of elements in the keepout array.
  * @type:	Type of the nvmem storage
  * @read_only:	Device is read-only.
  * @root_only:	Device is accessibly to root only.
@@ -66,6 +81,8 @@ struct nvmem_config {
 	struct gpio_desc	*wp_gpio;
 	const struct nvmem_cell_info	*cells;
 	int			ncells;
+	const struct nvmem_keepout *keepout;
+	unsigned int		nkeepout;
 	enum nvmem_type		type;
 	bool			read_only;
 	bool			root_only;