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author | Mauro Carvalho Chehab <mchehab@redhat.com> | 2011-12-30 13:59:37 -0200 |
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committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2011-12-30 13:59:37 -0200 |
commit | b4d48c942c17ce3d3a330ad91e109e522bc97378 (patch) | |
tree | 3365292f3a5a502edb51492d011fd326c930ca40 /Documentation/i2c/ten-bit-addresses | |
parent | 1a5cd29631a6b75e49e6ad8a770ab9d69cda0fa2 (diff) | |
parent | 5f0a6e2d503896062f641639dacfe5055c2f593b (diff) |
Merge tag 'v3.2-rc7' into staging/for_v3.3
Linux 3.2-rc7
* tag 'v3.2-rc7': (1304 commits)
Linux 3.2-rc7
netfilter: xt_connbytes: handle negation correctly
Btrfs: call d_instantiate after all ops are setup
Btrfs: fix worker lock misuse in find_worker
net: relax rcvbuf limits
rps: fix insufficient bounds checking in store_rps_dev_flow_table_cnt()
net: introduce DST_NOPEER dst flag
mqprio: Avoid panic if no options are provided
bridge: provide a mtu() method for fake_dst_ops
md/bitmap: It is OK to clear bits during recovery.
md: don't give up looking for spares on first failure-to-add
md/raid5: ensure correct assessment of drives during degraded reshape.
md/linear: fix hot-add of devices to linear arrays.
sparc64: Fix MSIQ HV call ordering in pci_sun4v_msiq_build_irq().
pata_of_platform: Add missing CONFIG_OF_IRQ dependency.
ipv4: using prefetch requires including prefetch.h
VFS: Fix race between CPU hotplug and lglocks
vfs: __read_cache_page should use gfp argument rather than GFP_KERNEL
USB: Fix usb/isp1760 build on sparc
net: Add a flow_cache_flush_deferred function
...
Conflicts:
drivers/media/common/tuners/tda18218.c
drivers/media/video/omap3isp/ispccdc.c
drivers/staging/media/as102/as102_drv.h
Diffstat (limited to 'Documentation/i2c/ten-bit-addresses')
-rw-r--r-- | Documentation/i2c/ten-bit-addresses | 36 |
1 files changed, 19 insertions, 17 deletions
diff --git a/Documentation/i2c/ten-bit-addresses b/Documentation/i2c/ten-bit-addresses index e9890709c50..cdfe13901b9 100644 --- a/Documentation/i2c/ten-bit-addresses +++ b/Documentation/i2c/ten-bit-addresses @@ -1,22 +1,24 @@ The I2C protocol knows about two kinds of device addresses: normal 7 bit addresses, and an extended set of 10 bit addresses. The sets of addresses do not intersect: the 7 bit address 0x10 is not the same as the 10 bit -address 0x10 (though a single device could respond to both of them). You -select a 10 bit address by adding an extra byte after the address -byte: - S Addr7 Rd/Wr .... -becomes - S 11110 Addr10 Rd/Wr -S is the start bit, Rd/Wr the read/write bit, and if you count the number -of bits, you will see the there are 8 after the S bit for 7 bit addresses, -and 16 after the S bit for 10 bit addresses. +address 0x10 (though a single device could respond to both of them). -WARNING! The current 10 bit address support is EXPERIMENTAL. There are -several places in the code that will cause SEVERE PROBLEMS with 10 bit -addresses, even though there is some basic handling and hooks. Also, -almost no supported adapter handles the 10 bit addresses correctly. +I2C messages to and from 10-bit address devices have a different format. +See the I2C specification for the details. -As soon as a real 10 bit address device is spotted 'in the wild', we -can and will add proper support. Right now, 10 bit address devices -are defined by the I2C protocol, but we have never seen a single device -which supports them. +The current 10 bit address support is minimal. It should work, however +you can expect some problems along the way: +* Not all bus drivers support 10-bit addresses. Some don't because the + hardware doesn't support them (SMBus doesn't require 10-bit address + support for example), some don't because nobody bothered adding the + code (or it's there but not working properly.) Software implementation + (i2c-algo-bit) is known to work. +* Some optional features do not support 10-bit addresses. This is the + case of automatic detection and instantiation of devices by their, + drivers, for example. +* Many user-space packages (for example i2c-tools) lack support for + 10-bit addresses. + +Note that 10-bit address devices are still pretty rare, so the limitations +listed above could stay for a long time, maybe even forever if nobody +needs them to be fixed. |