diff options
Diffstat (limited to 'target/linux/generic/backport-5.10/803-v5.13-0004-nvmem-core-Add-functions-to-make-number-reading-easy.patch')
| -rw-r--r-- | target/linux/generic/backport-5.10/803-v5.13-0004-nvmem-core-Add-functions-to-make-number-reading-easy.patch | 174 |
1 files changed, 174 insertions, 0 deletions
diff --git a/target/linux/generic/backport-5.10/803-v5.13-0004-nvmem-core-Add-functions-to-make-number-reading-easy.patch b/target/linux/generic/backport-5.10/803-v5.13-0004-nvmem-core-Add-functions-to-make-number-reading-easy.patch new file mode 100644 index 0000000000..ff2456722f --- /dev/null +++ b/target/linux/generic/backport-5.10/803-v5.13-0004-nvmem-core-Add-functions-to-make-number-reading-easy.patch @@ -0,0 +1,174 @@ +From a28e824fb8270eda43fd0f65c2a5fdf33f55c5eb Mon Sep 17 00:00:00 2001 +From: Douglas Anderson <dianders@chromium.org> +Date: Tue, 30 Mar 2021 12:12:37 +0100 +Subject: [PATCH] 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> +--- + drivers/nvmem/core.c | 95 ++++++++++++++++++++++++++++++++++ + include/linux/nvmem-consumer.h | 4 ++ + 2 files changed, 99 insertions(+) + +--- a/drivers/nvmem/core.c ++++ b/drivers/nvmem/core.c +@@ -1612,6 +1612,101 @@ int nvmem_cell_read_u64(struct device *d + } + EXPORT_SYMBOL_GPL(nvmem_cell_read_u64); + ++static 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; ++ ++ cell = nvmem_cell_get(dev, cell_id); ++ if (IS_ERR(cell)) ++ return cell; ++ ++ 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); ++ return ERR_PTR(-ERANGE); ++ } ++ ++ 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; ++ 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); ++ ++ return 0; ++} ++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; ++ 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); ++ ++ return 0; ++} ++EXPORT_SYMBOL_GPL(nvmem_cell_read_variable_le_u64); ++ + /** + * nvmem_device_cell_read() - Read a given nvmem device and cell + * +--- a/include/linux/nvmem-consumer.h ++++ b/include/linux/nvmem-consumer.h +@@ -65,6 +65,10 @@ int nvmem_cell_read_u8(struct device *de + 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_u64(struct device *dev, const char *cell_id, u64 *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); |