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   1 From 55d4980ce55b6bb4be66877de4dbec513911b988 Mon Sep 17 00:00:00 2001
   2 From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
   3 Date: Tue, 4 Apr 2023 18:21:42 +0100
   4 Subject: [PATCH] nvmem: core: support specifying both: cell raw data & post
   5  read lengths
   6 MIME-Version: 1.0
   7 Content-Type: text/plain; charset=UTF-8
   8 Content-Transfer-Encoding: 8bit
   9
  10 Callback .read_post_process() is designed to modify raw cell content
  11 before providing it to the consumer. So far we were dealing with
  12 modifications that didn't affect cell size (length). In some cases
  13 however cell content needs to be reformatted and resized.
  14
  15 It's required e.g. to provide properly formatted MAC address in case
  16 it's stored in a non-binary format (e.g. using ASCII).
  17
  18 There were few discussions how to optimally handle that. Following
  19 possible solutions were considered:
  20 1. Allow .read_post_process() to realloc (resize) content buffer
  21 2. Allow .read_post_process() to adjust (decrease) just buffer length
  22 3. Register NVMEM cells using post-read sizes
  23
  24 The preferred solution was the last one. The problem is that simply
  25 adjusting "bytes" in NVMEM providers would result in core code NOT
  26 passing whole raw data to .read_post_process() callbacks. It means
  27 callback functions couldn't do their job without somehow manually
  28 reading original cell content on their own.
  29
  30 This patch deals with that by registering NVMEM cells with both lengths:
  31 raw content one and post read one. It allows:
  32 1. Core code to read whole raw cell content
  33 2. Callbacks to return content they want
  34
  35 Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
  36 Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
  37 Link: https://lore.kernel.org/r/20230404172148.82422-35-srinivas.kandagatla@linaro.org
  38 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  39 ---
  40  drivers/nvmem/core.c           | 11 +++++++----
  41  include/linux/nvmem-provider.h |  2 ++
  42  2 files changed, 9 insertions(+), 4 deletions(-)
  43
  44 --- a/drivers/nvmem/core.c
  45 +++ b/drivers/nvmem/core.c
  46 @@ -50,6 +50,7 @@ struct nvmem_device {
  47  struct nvmem_cell_entry {
  48         const char              *name;
  49         int                     offset;
  50 +       size_t                  raw_len;
  51         int                     bytes;
  52         int                     bit_offset;
  53         int                     nbits;
  54 @@ -469,6 +470,7 @@ static int nvmem_cell_info_to_nvmem_cell
  55  {
  56         cell->nvmem = nvmem;
  57         cell->offset = info->offset;
  58 +       cell->raw_len = info->raw_len ?: info->bytes;
  59         cell->bytes = info->bytes;
  60         cell->name = info->name;
  61         cell->read_post_process = info->read_post_process;
  62 @@ -1560,7 +1562,7 @@ static int __nvmem_cell_read(struct nvme
  63  {
  64         int rc;
  65
  66 -       rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->bytes);
  67 +       rc = nvmem_reg_read(nvmem, cell->offset, buf, cell->raw_len);
  68
  69         if (rc)
  70                 return rc;
  71 @@ -1571,7 +1573,7 @@ static int __nvmem_cell_read(struct nvme
  72
  73         if (cell->read_post_process) {
  74                 rc = cell->read_post_process(cell->priv, id, index,
  75 -                                            cell->offset, buf, cell->bytes);
  76 +                                            cell->offset, buf, cell->raw_len);
  77                 if (rc)
  78                         return rc;
  79         }
  80 @@ -1594,14 +1596,15 @@ static int __nvmem_cell_read(struct nvme
  81   */
  82  void *nvmem_cell_read(struct nvmem_cell *cell, size_t *len)
  83  {
  84 -       struct nvmem_device *nvmem = cell->entry->nvmem;
  85 +       struct nvmem_cell_entry *entry = cell->entry;
  86 +       struct nvmem_device *nvmem = entry->nvmem;
  87         u8 *buf;
  88         int rc;
  89
  90         if (!nvmem)
  91                 return ERR_PTR(-EINVAL);
  92
  93 -       buf = kzalloc(cell->entry->bytes, GFP_KERNEL);
  94 +       buf = kzalloc(max_t(size_t, entry->raw_len, entry->bytes), GFP_KERNEL);
  95         if (!buf)
  96                 return ERR_PTR(-ENOMEM);
  97
  98 --- a/include/linux/nvmem-provider.h
  99 +++ b/include/linux/nvmem-provider.h
 100 @@ -51,6 +51,7 @@ struct nvmem_keepout {
 101   * struct nvmem_cell_info - NVMEM cell description
 102   * @name:      Name.
 103   * @offset:    Offset within the NVMEM device.
 104 + * @raw_len:   Length of raw data (without post processing).
 105   * @bytes:     Length of the cell.
 106   * @bit_offset:        Bit offset if cell is smaller than a byte.
 107   * @nbits:     Number of bits.
 108 @@ -62,6 +63,7 @@ struct nvmem_keepout {
 109  struct nvmem_cell_info {
 110         const char              *name;
 111         unsigned int            offset;
 112 +       size_t                  raw_len;
 113         unsigned int            bytes;
 114         unsigned int            bit_offset;
 115         unsigned int            nbits;