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author | Tony Lindgren <tony@atomide.com> | 2017-11-28 19:12:32 +0300 |
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committer | Tony Lindgren <tony@atomide.com> | 2017-11-28 19:12:32 +0300 |
commit | bc686442f8a601bccac1f22506ecdb4b0d62cadd (patch) | |
tree | b224ab4aa2350b233da640f5850f48bc6bfeb2d0 /Documentation/filesystems/cramfs.txt | |
parent | 60636a5d0fa2f8bc6d0c23c4027100ba20866f9b (diff) | |
parent | ca41e244517d6d3f1600c229ff7ca615049c1e9c (diff) | |
download | linux-bc686442f8a601bccac1f22506ecdb4b0d62cadd.tar.xz |
Merge branch 'dts-fixes' into omap-for-v4.15/fixes-dt
Diffstat (limited to 'Documentation/filesystems/cramfs.txt')
-rw-r--r-- | Documentation/filesystems/cramfs.txt | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/filesystems/cramfs.txt b/Documentation/filesystems/cramfs.txt index 4006298f6707..8e19a53d648b 100644 --- a/Documentation/filesystems/cramfs.txt +++ b/Documentation/filesystems/cramfs.txt @@ -45,6 +45,48 @@ you can just change the #define in mkcramfs.c, so long as you don't mind the filesystem becoming unreadable to future kernels. +Memory Mapped cramfs image +-------------------------- + +The CRAMFS_MTD Kconfig option adds support for loading data directly from +a physical linear memory range (usually non volatile memory like Flash) +instead of going through the block device layer. This saves some memory +since no intermediate buffering is necessary to hold the data before +decompressing. + +And when data blocks are kept uncompressed and properly aligned, they will +automatically be mapped directly into user space whenever possible providing +eXecute-In-Place (XIP) from ROM of read-only segments. Data segments mapped +read-write (hence they have to be copied to RAM) may still be compressed in +the cramfs image in the same file along with non compressed read-only +segments. Both MMU and no-MMU systems are supported. This is particularly +handy for tiny embedded systems with very tight memory constraints. + +The location of the cramfs image in memory is system dependent. You must +know the proper physical address where the cramfs image is located and +configure an MTD device for it. Also, that MTD device must be supported +by a map driver that implements the "point" method. Examples of such +MTD drivers are cfi_cmdset_0001 (Intel/Sharp CFI flash) or physmap +(Flash device in physical memory map). MTD partitions based on such devices +are fine too. Then that device should be specified with the "mtd:" prefix +as the mount device argument. For example, to mount the MTD device named +"fs_partition" on the /mnt directory: + +$ mount -t cramfs mtd:fs_partition /mnt + +To boot a kernel with this as root filesystem, suffice to specify +something like "root=mtd:fs_partition" on the kernel command line. + + +Tools +----- + +A version of mkcramfs that can take advantage of the latest capabilities +described above can be found here: + +https://github.com/npitre/cramfs-tools + + For /usr/share/magic -------------------- |