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  1. 16 Apr, 2019 3 commits
    • Wolfram Sang's avatar
      i2c: core: introduce callbacks for atomic transfers · 63b96983
      Wolfram Sang authored 
      We had the request to access devices very late when interrupts are not
available anymore multiple times now. Mostly to prepare shutdown or
reboot. Allow adapters to specify a specific callback for this case.
Note that we fall back to the generic {master|smbus}_xfer callback if
this new atomic one is not present. This is intentional to preserve the
previous behaviour and avoid regressions. Because there are drivers not
using interrupts or because it might have worked "accidently" before.
Signed-off-by: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: default avatarStefan Lengfeld <contact@stefanchrist.eu>
Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>
      63b96983
    • Wolfram Sang's avatar
      i2c: core: use I2C locking behaviour also for SMBUS · 83c42212
      Wolfram Sang authored 
      If I2C transfers are executed in atomic contexts, trylock is used
instead of lock. This behaviour was missing for SMBUS, although a lot of
transfers are of SMBUS type, either emulated or direct. So, factor out
the locking routine into a helper and use it for I2C and SMBUS.
Signed-off-by: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>
      83c42212
    • Wolfram Sang's avatar
      i2c: core: remove use of in_atomic() · bae1d3a0
      Wolfram Sang authored 
      Commit cea443a8 ("i2c: Support i2c_transfer in atomic contexts")
added in_atomic() to the I2C core. However, the use of in_atomic()
outside of core kernel code is discouraged and was already[1] when this
code was added in early 2008. The above commit was a preparation for
commit b7a36701 ("i2c-pxa: Add polling transfer"). Its commit
message says explicitly it was added "for cases where I2C transactions
have to occur at times interrup[t]s are disabled". So, the intention was
'disabled interrupts'. This matches the use cases for atomic I2C
transfers I have seen so far: very late communication (mostly to a PMIC)
to powerdown or reboot the system. For those cases, interrupts are
disabled then. It doesn't seem that in_atomic() adds value.

After a discussion with Peter Zijlstra[2], we came up with a better set
of conditionals to match the use case.

The I2C core will soon gain an extra callback into bus drivers
especially for atomic transfers to make them more generic. The code
deciding which transfer to use (atomic/non-atomic) should mimic the
behaviour which locking to use (trylock/lock). This is why we add a
helper for it.

[1] https://lwn.net/Articles/274695/
[2] http://patchwork.ozlabs.org/patch/1067437/Signed-off-by: default avatarWolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: default avatarStefan Lengfeld <contact@stefanchrist.eu>
Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>
      bae1d3a0
  3. 15 Apr, 2019 6 commits
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