• 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
i2c-core-base.c 62.7 KB