From 8dc0b1158dcffd78ea2b3a5604b82ee826de687b Mon Sep 17 00:00:00 2001
From: Zhanyong Wang <zhanyong.wang@mediatek.com>
Date: Mon, 8 Nov 2021 13:58:51 +0800
Subject: [PATCH 1/5] nvmem: core: Add functions to make number reading easy

Sometimes the clients of nvmem just want to get a number out of
nvmem. They don't want to think about exactly how many bytes the nvmem
cell took up. They just want the number. Let's make it easy.

In general this concept is useful because nvmem space is precious and
usually the fewest bits are allocated that will hold a given value on
a given system. However, even though small numbers might be fine on
one system that doesn't mean that logically the number couldn't be
bigger. Imagine nvmem containing a max frequency for a component. On
one system perhaps that fits in 16 bits. On another system it might
fit in 32 bits. The code reading this number doesn't care--it just
wants the number.

We'll provide two functions: nvmem_cell_read_variable_le_u32() and
nvmem_cell_read_variable_le_u64().

Comparing these to the existing functions like nvmem_cell_read_u32():
* These new functions have no problems if the value was stored in
  nvmem in fewer bytes. It's OK to use these function as long as the
  value stored will fit in 32-bits (or 64-bits).
* These functions avoid problems that the earlier APIs had with bit
  offsets. For instance, you can't use nvmem_cell_read_u32() to read a
  value has nbits=32 and bit_offset=4 because the nvmem cell must be
  at least 5 bytes big to hold this value. The new API accounts for
  this and works fine.
* These functions make it very explicit that they assume that the
  number was stored in little endian format. The old functions made
  this assumption whenever bit_offset was non-zero (see
  nvmem_shift_read_buffer_in_place()) but didn't whenever the
  bit_offset was zero.

NOTE: it's assumed that we don't need an 8-bit or 16-bit version of
this function. The 32-bit version of the function can be used to read
8-bit or 16-bit data.

At the moment, I'm only adding the "unsigned" versions of these
functions, but if it ends up being useful someone could add a "signed"
version that did 2's complement sign extension.

At the moment, I'm only adding the "little endian" versions of these
functions. Adding the "big endian" version would require adding "big
endian" support to nvmem_shift_read_buffer_in_place().

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210330111241.19401-7-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
Signed-off-by: Zhanyong Wang <zhanyong.wang@mediatek.com>
Change-Id: I3e1d96ec1680812d5e24681c79852c9b36899559
---
 drivers/nvmem/core.c           | 161 +++++++++++++++++++++++++++------
 include/linux/nvmem-consumer.h |  15 +++
 2 files changed, 150 insertions(+), 26 deletions(-)

diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index c0f4324d8f7c..e26b25b5c288 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -1102,16 +1102,8 @@ int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len)
 }
 EXPORT_SYMBOL_GPL(nvmem_cell_write);
 
-/**
- * nvmem_cell_read_u16() - Read a cell value as an u16
- *
- * @dev: Device that requests the nvmem cell.
- * @cell_id: Name of nvmem cell to read.
- * @val: pointer to output value.
- *
- * Return: 0 on success or negative errno.
- */
-int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val)
+static int nvmem_cell_read_common(struct device *dev, const char *cell_id,
+				  void *val, size_t count)
 {
 	struct nvmem_cell *cell;
 	void *buf;
@@ -1126,21 +1118,50 @@ int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val)
 		nvmem_cell_put(cell);
 		return PTR_ERR(buf);
 	}
-	if (len != sizeof(*val)) {
+	if (len != count) {
 		kfree(buf);
 		nvmem_cell_put(cell);
 		return -EINVAL;
 	}
-	memcpy(val, buf, sizeof(*val));
+	memcpy(val, buf, count);
 	kfree(buf);
 	nvmem_cell_put(cell);
 
 	return 0;
 }
+
+/**
+ * nvmem_cell_read_u8() - Read a cell value as a u8
+ *
+ * @dev: Device that requests the nvmem cell.
+ * @cell_id: Name of nvmem cell to read.
+ * @val: pointer to output value.
+ *
+ * Return: 0 on success or negative errno.
+ */
+int nvmem_cell_read_u8(struct device *dev, const char *cell_id, u8 *val)
+{
+	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
+}
+EXPORT_SYMBOL_GPL(nvmem_cell_read_u8);
+
+/**
+ * nvmem_cell_read_u16() - Read a cell value as a u16
+ *
+ * @dev: Device that requests the nvmem cell.
+ * @cell_id: Name of nvmem cell to read.
+ * @val: pointer to output value.
+ *
+ * Return: 0 on success or negative errno.
+ */
+int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val)
+{
+	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
+}
 EXPORT_SYMBOL_GPL(nvmem_cell_read_u16);
 
 /**
- * nvmem_cell_read_u32() - Read a cell value as an u32
+ * nvmem_cell_read_u32() - Read a cell value as a u32
  *
  * @dev: Device that requests the nvmem cell.
  * @cell_id: Name of nvmem cell to read.
@@ -1149,32 +1170,120 @@ EXPORT_SYMBOL_GPL(nvmem_cell_read_u16);
  * Return: 0 on success or negative errno.
  */
 int nvmem_cell_read_u32(struct device *dev, const char *cell_id, u32 *val)
+{
+	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
+}
+EXPORT_SYMBOL_GPL(nvmem_cell_read_u32);
+
+/**
+ * nvmem_cell_read_u64() - Read a cell value as a u64
+ *
+ * @dev: Device that requests the nvmem cell.
+ * @cell_id: Name of nvmem cell to read.
+ * @val: pointer to output value.
+ *
+ * Return: 0 on success or negative errno.
+ */
+int nvmem_cell_read_u64(struct device *dev, const char *cell_id, u64 *val)
+{
+	return nvmem_cell_read_common(dev, cell_id, val, sizeof(*val));
+}
+EXPORT_SYMBOL_GPL(nvmem_cell_read_u64);
+
+static const void *nvmem_cell_read_variable_common(struct device *dev,
+						   const char *cell_id,
+						   size_t max_len, size_t *len)
 {
 	struct nvmem_cell *cell;
+	int nbits;
 	void *buf;
-	size_t len;
 
 	cell = nvmem_cell_get(dev, cell_id);
 	if (IS_ERR(cell))
-		return PTR_ERR(cell);
+		return cell;
 
-	buf = nvmem_cell_read(cell, &len);
-	if (IS_ERR(buf)) {
-		nvmem_cell_put(cell);
-		return PTR_ERR(buf);
-	}
-	if (len != sizeof(*val)) {
+	nbits = cell->nbits;
+	buf = nvmem_cell_read(cell, len);
+	nvmem_cell_put(cell);
+	if (IS_ERR(buf))
+		return buf;
+
+	/*
+	 * If nbits is set then nvmem_cell_read() can significantly exaggerate
+	 * the length of the real data. Throw away the extra junk.
+	 */
+	if (nbits)
+		*len = DIV_ROUND_UP(nbits, 8);
+
+	if (*len > max_len) {
 		kfree(buf);
-		nvmem_cell_put(cell);
-		return -EINVAL;
+		return ERR_PTR(-ERANGE);
 	}
-	memcpy(val, buf, sizeof(*val));
+
+	return buf;
+}
+
+/**
+ * nvmem_cell_read_variable_le_u32() - Read up to 32-bits of data as a little endian number.
+ *
+ * @dev: Device that requests the nvmem cell.
+ * @cell_id: Name of nvmem cell to read.
+ * @val: pointer to output value.
+ *
+ * Return: 0 on success or negative errno.
+ */
+int nvmem_cell_read_variable_le_u32(struct device *dev, const char *cell_id,
+				    u32 *val)
+{
+	size_t len;
+	const u8 *buf;
+	int i;
+
+	buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	/* Copy w/ implicit endian conversion */
+	*val = 0;
+	for (i = 0; i < len; i++)
+		*val |= buf[i] << (8 * i);
 
 	kfree(buf);
-	nvmem_cell_put(cell);
+
 	return 0;
 }
-EXPORT_SYMBOL_GPL(nvmem_cell_read_u32);
+EXPORT_SYMBOL_GPL(nvmem_cell_read_variable_le_u32);
+
+/**
+ * nvmem_cell_read_variable_le_u64() - Read up to 64-bits of data as a little endian number.
+ *
+ * @dev: Device that requests the nvmem cell.
+ * @cell_id: Name of nvmem cell to read.
+ * @val: pointer to output value.
+ *
+ * Return: 0 on success or negative errno.
+ */
+int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id,
+				    u64 *val)
+{
+	size_t len;
+	const u8 *buf;
+	int i;
+
+	buf = nvmem_cell_read_variable_common(dev, cell_id, sizeof(*val), &len);
+	if (IS_ERR(buf))
+		return PTR_ERR(buf);
+
+	/* Copy w/ implicit endian conversion */
+	*val = 0;
+	for (i = 0; i < len; i++)
+		*val |= (uint64_t)buf[i] << (8 * i);
+
+	kfree(buf);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(nvmem_cell_read_variable_le_u64);
 
 /**
  * nvmem_device_cell_read() - Read a given nvmem device and cell
diff --git a/include/linux/nvmem-consumer.h b/include/linux/nvmem-consumer.h
index 5c17cb733224..e328c0f7eef3 100644
--- a/include/linux/nvmem-consumer.h
+++ b/include/linux/nvmem-consumer.h
@@ -63,6 +63,10 @@ void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len);
 int nvmem_cell_write(struct nvmem_cell *cell, void *buf, size_t len);
 int nvmem_cell_read_u16(struct device *dev, const char *cell_id, u16 *val);
 int nvmem_cell_read_u32(struct device *dev, const char *cell_id, u32 *val);
+int nvmem_cell_read_variable_le_u32(struct device *dev, const char *cell_id,
+				    u32 *val);
+int nvmem_cell_read_variable_le_u64(struct device *dev, const char *cell_id,
+				    u64 *val);
 
 /* direct nvmem device read/write interface */
 struct nvmem_device *nvmem_device_get(struct device *dev, const char *name);
@@ -134,6 +138,17 @@ static inline int nvmem_cell_read_u32(struct device *dev,
 {
 	return -EOPNOTSUPP;
 }
+static inline int nvmem_cell_read_variable_le_u32(struct device *dev,
+						const char *cell_id, u32 *val)
+{
+	return -ENOSYS;
+}
+
+static inline int nvmem_cell_read_variable_le_u64(struct device *dev,
+						const char *cell_id, u64 *val);
+{
+	return -ENOSYS;
+}
 
 static inline struct nvmem_device *nvmem_device_get(struct device *dev,
 						    const char *name)
-- 
2.18.0