mtd: document ABI

We're missing a lot of important documentation in include/mtd/mtd-abi.h:

* add a simple description of each ioctl (feel free to expand!)
* give full explanations of recently added and modified operations
* explain the usage of "RAW" that appear in different modes and types of
  operations
* fix some comment style along the way

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>

diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
index c2047b8..37d0827 100644 (file)
--- a/include/linux/mtd/mtd.h
+++ b/include/linux/mtd/mtd.h
@@ -79,7 +79,7 @@ struct mtd_erase_region_info {
  * @ooblen:    number of oob bytes to write/read
  * @oobretlen: number of oob bytes written/read
  * @ooboffs:   offset of oob data in the oob area (only relevant when
- *             mode = MTD_OPS_PLACE_OOB)
+ *             mode = MTD_OPS_PLACE_OOB or MTD_OPS_RAW)
  * @datbuf:    data buffer - if NULL only oob data are read/written
  * @oobbuf:    oob data buffer
  *

diff --git a/include/mtd/mtd-abi.h b/include/mtd/mtd-abi.h
index 1a16046..7dee970 100644 (file)
--- a/include/mtd/mtd-abi.h
+++ b/include/mtd/mtd-abi.h
@@ -45,14 +45,18 @@ struct mtd_oob_buf64 {
        __u64 usr_ptr;
 };
 
-/*
+/**
  * MTD operation modes
  *
- * MTD_OPS_PLACE_OOB:  oob data are placed at the given offset (default)
- * MTD_OPS_AUTO_OOB:   oob data are automatically placed at the free areas
+ * @MTD_OPS_PLACE_OOB: OOB data are placed at the given offset (default)
+ * @MTD_OPS_AUTO_OOB:  OOB data are automatically placed at the free areas
  *                     which are defined by the internal ecclayout
- * MTD_OPS_RAW:                mode to read or write oob and data without doing ECC
- *                     checking
+ * @MTD_OPS_RAW:       data are transferred as-is, with no error correction;
+ *                     this mode implies %MTD_OPS_PLACE_OOB
+ *
+ * These modes can be passed to ioctl(MEMWRITE) and are also used internally.
+ * See notes on "MTD file modes" for discussion on %MTD_OPS_RAW vs.
+ * %MTD_FILE_MODE_RAW.
  */
 enum {
        MTD_OPS_PLACE_OOB = 0,
@@ -60,6 +64,22 @@ enum {
        MTD_OPS_RAW = 2,
 };
 
+/**
+ * struct mtd_write_req - data structure for requesting a write operation
+ *
+ * @start:     start address
+ * @len:       length of data buffer
+ * @ooblen:    length of OOB buffer
+ * @usr_data:  user-provided data buffer
+ * @usr_oob:   user-provided OOB buffer
+ * @mode:      MTD mode (see "MTD operation modes")
+ * @padding:   reserved, must be set to 0
+ *
+ * This structure supports ioctl(MEMWRITE) operations, allowing data and/or OOB
+ * writes in various modes. To write to OOB-only, set @usr_data == NULL, and to
+ * write data-only, set @usr_oob == NULL. However, setting both @usr_data and
+ * @usr_oob to NULL is not allowed.
+ */
 struct mtd_write_req {
        __u64 start;
        __u64 len;
@@ -84,13 +104,13 @@ struct mtd_write_req {
 #define MTD_NO_ERASE           0x1000  /* No erase necessary */
 #define MTD_POWERUP_LOCK       0x2000  /* Always locked after reset */
 
-// Some common devices / combinations of capabilities
+/* Some common devices / combinations of capabilities */
 #define MTD_CAP_ROM            0
 #define MTD_CAP_RAM            (MTD_WRITEABLE | MTD_BIT_WRITEABLE | MTD_NO_ERASE)
 #define MTD_CAP_NORFLASH       (MTD_WRITEABLE | MTD_BIT_WRITEABLE)
 #define MTD_CAP_NANDFLASH      (MTD_WRITEABLE)
 
-/* ECC byte placement */
+/* Obsolete ECC byte placement modes (used with obsolete MEMGETOOBSEL) */
 #define MTD_NANDECC_OFF                0       // Switch off ECC (Not recommended)
 #define MTD_NANDECC_PLACE      1       // Use the given placement in the structure (YAFFS1 legacy mode)
 #define MTD_NANDECC_AUTOPLACE  2       // Use the default placement scheme
@@ -105,10 +125,10 @@ struct mtd_write_req {
 struct mtd_info_user {
        __u8 type;
        __u32 flags;
-       __u32 size;      // Total size of the MTD
+       __u32 size;     /* Total size of the MTD */
        __u32 erasesize;
        __u32 writesize;
-       __u32 oobsize;   // Amount of OOB data per block (e.g. 16)
+       __u32 oobsize;  /* Amount of OOB data per block (e.g. 16) */
        /* The below two fields are obsolete and broken, do not use them
         * (TODO: remove at some point) */
        __u32 ecctype;
@@ -117,9 +137,9 @@ struct mtd_info_user {
 
 struct region_info_user {
        __u32 offset;           /* At which this region starts,
-                                        * from the beginning of the MTD */
-       __u32 erasesize;                /* For this region */
-       __u32 numblocks;                /* Number of blocks in this region */
+                                * from the beginning of the MTD */
+       __u32 erasesize;        /* For this region */
+       __u32 numblocks;        /* Number of blocks in this region */
        __u32 regionindex;
 };
 
@@ -135,28 +155,54 @@ struct otp_info {
  * Try to avoid adding a new ioctl with the same ioctl number.
  */
 
+/* Get basic MTD characteristics info (better to use sysfs) */
 #define MEMGETINFO             _IOR('M', 1, struct mtd_info_user)
+/* Erase segment of MTD */
 #define MEMERASE               _IOW('M', 2, struct erase_info_user)
+/* Write out-of-band data from MTD */
 #define MEMWRITEOOB            _IOWR('M', 3, struct mtd_oob_buf)
+/* Read out-of-band data from MTD */
 #define MEMREADOOB             _IOWR('M', 4, struct mtd_oob_buf)
+/* Lock a chip (for MTD that supports it) */
 #define MEMLOCK                        _IOW('M', 5, struct erase_info_user)
+/* Unlock a chip (for MTD that supports it) */
 #define MEMUNLOCK              _IOW('M', 6, struct erase_info_user)
+/* Get the number of different erase regions */
 #define MEMGETREGIONCOUNT      _IOR('M', 7, int)
+/* Get information about the erase region for a specific index */
 #define MEMGETREGIONINFO       _IOWR('M', 8, struct region_info_user)
+/* Get info about OOB modes (e.g., RAW, PLACE, AUTO) - legacy interface */
 #define MEMGETOOBSEL           _IOR('M', 10, struct nand_oobinfo)
+/* Check if an eraseblock is bad */
 #define MEMGETBADBLOCK         _IOW('M', 11, __kernel_loff_t)
+/* Mark an eraseblock as bad */
 #define MEMSETBADBLOCK         _IOW('M', 12, __kernel_loff_t)
+/* Set OTP (One-Time Programmable) mode (factory vs. user) */
 #define OTPSELECT              _IOR('M', 13, int)
+/* Get number of OTP (One-Time Programmable) regions */
 #define OTPGETREGIONCOUNT      _IOW('M', 14, int)
+/* Get all OTP (One-Time Programmable) info about MTD */
 #define OTPGETREGIONINFO       _IOW('M', 15, struct otp_info)
+/* Lock a given range of user data (must be in mode %MTD_FILE_MODE_OTP_USER) */
 #define OTPLOCK                        _IOR('M', 16, struct otp_info)
+/* Get ECC layout (deprecated) */
 #define ECCGETLAYOUT           _IOR('M', 17, struct nand_ecclayout_user)
+/* Get statistics about corrected/uncorrected errors */
 #define ECCGETSTATS            _IOR('M', 18, struct mtd_ecc_stats)
+/* Set MTD mode on a per-file-descriptor basis (see "MTD file modes") */
 #define MTDFILEMODE            _IO('M', 19)
+/* Erase segment of MTD (supports 64-bit address) */
 #define MEMERASE64             _IOW('M', 20, struct erase_info_user64)
+/* Write data to OOB (64-bit version) */
 #define MEMWRITEOOB64          _IOWR('M', 21, struct mtd_oob_buf64)
+/* Read data from OOB (64-bit version) */
 #define MEMREADOOB64           _IOWR('M', 22, struct mtd_oob_buf64)
+/* Check if chip is locked (for MTD that supports it) */
 #define MEMISLOCKED            _IOR('M', 23, struct erase_info_user)
+/*
+ * Most generic write interface; can write in-band and/or out-of-band in various
+ * modes (see "struct mtd_write_req")
+ */
 #define MEMWRITE               _IOWR('M', 24, struct mtd_write_req)
 
 /*
@@ -208,7 +254,21 @@ struct mtd_ecc_stats {
 };
 
 /*
- * Read/write file modes for access to MTD
+ * MTD file modes - for read/write access to MTD
+ *
+ * @MTD_FILE_MODE_NORMAL:      OTP disabled, ECC enabled
+ * @MTD_FILE_MODE_OTP_FACTORY: OTP enabled in factory mode
+ * @MTD_FILE_MODE_OTP_USER:    OTP enabled in user mode
+ * @MTD_FILE_MODE_RAW:         OTP disabled, ECC disabled
+ *
+ * These modes can be set via ioctl(MTDFILEMODE). The mode mode will be retained
+ * separately for each open file descriptor.
+ *
+ * Note: %MTD_FILE_MODE_RAW provides the same functionality as %MTD_OPS_RAW -
+ * raw access to the flash, without error correction or autoplacement schemes.
+ * Wherever possible, the MTD_OPS_* mode will override the MTD_FILE_MODE_* mode
+ * (e.g., when using ioctl(MEMWRITE)), but in some cases, the MTD_FILE_MODE is
+ * used out of necessity (e.g., `write()', ioctl(MEMWRITEOOB64)).
  */
 enum mtd_file_modes {
        MTD_FILE_MODE_NORMAL = MTD_OTP_OFF,