threeeye
bc1d038eac
Squashed backup commit (no shallow-clone history issues) of xiaomi-mt6833-dev/kernel_xiaomi_mt6833 (lineage-23.2 branch, upstream commit 9eece662e) plus all fixes applied to get everpal_defconfig building clean against a modern (GCC 15.2.0) toolchain -- see the previous commit message on the lineage-23.2 branch (also in this repo history is not available here since this is a squashed snapshot; full incremental history lives in the local DL380 checkout and the upstream GitHub remote). Upstream: https://github.com/xiaomi-mt6833-dev/kernel_xiaomi_mt6833 (lineage-23.2)
29 lines
1.5 KiB
Plaintext
29 lines
1.5 KiB
Plaintext
The I2C protocol knows about two kinds of device addresses: normal 7 bit
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addresses, and an extended set of 10 bit addresses. The sets of addresses
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do not intersect: the 7 bit address 0x10 is not the same as the 10 bit
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address 0x10 (though a single device could respond to both of them).
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To avoid ambiguity, the user sees 10 bit addresses mapped to a different
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address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the
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10 bit mode. This is used for creating device names in sysfs. It is also
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needed when instantiating 10 bit devices via the new_device file in sysfs.
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I2C messages to and from 10-bit address devices have a different format.
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See the I2C specification for the details.
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The current 10 bit address support is minimal. It should work, however
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you can expect some problems along the way:
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* Not all bus drivers support 10-bit addresses. Some don't because the
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hardware doesn't support them (SMBus doesn't require 10-bit address
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support for example), some don't because nobody bothered adding the
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code (or it's there but not working properly.) Software implementation
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(i2c-algo-bit) is known to work.
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* Some optional features do not support 10-bit addresses. This is the
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case of automatic detection and instantiation of devices by their,
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drivers, for example.
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* Many user-space packages (for example i2c-tools) lack support for
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10-bit addresses.
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Note that 10-bit address devices are still pretty rare, so the limitations
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listed above could stay for a long time, maybe even forever if nobody
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needs them to be fixed.
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