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ede2299f71
System shutdown may happen with interrupts being disabled and in this case kernel may hang if atomic transfer isn't supported by driver. There were several occurrences where I found my Nexus 7 completely discharged despite of being turned off and then one day I spotted this in the log: reboot: Power down ------------[ cut here ]------------ WARNING: CPU: 0 PID: 1 at drivers/i2c/i2c-core.h:40 i2c_transfer+0x95/0x9c No atomic I2C transfer handler for 'i2c-1' Modules linked in: tegra30_devfreq CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.4.0-next-20191202-00120-gf7ecd80fb803-dirty #3195 Hardware name: NVIDIA Tegra SoC (Flattened Device Tree) [<c010e4b5>] (unwind_backtrace) from [<c010a0fd>] (show_stack+0x11/0x14) [<c010a0fd>] (show_stack) from [<c09995e5>] (dump_stack+0x85/0x94) [<c09995e5>] (dump_stack) from [<c011f3d1>] (__warn+0xc1/0xc4) [<c011f3d1>] (__warn) from [<c011f691>] (warn_slowpath_fmt+0x61/0x78) [<c011f691>] (warn_slowpath_fmt) from [<c069a8dd>] (i2c_transfer+0x95/0x9c) [<c069a8dd>] (i2c_transfer) from [<c05667f1>] (regmap_i2c_read+0x4d/0x6c) [<c05667f1>] (regmap_i2c_read) from [<c0563601>] (_regmap_raw_read+0x99/0x1cc) [<c0563601>] (_regmap_raw_read) from [<c0563757>] (_regmap_bus_read+0x23/0x38) [<c0563757>] (_regmap_bus_read) from [<c056293d>] (_regmap_read+0x3d/0xfc) [<c056293d>] (_regmap_read) from [<c0562d3b>] (_regmap_update_bits+0x87/0xc4) [<c0562d3b>] (_regmap_update_bits) from [<c0563add>] (regmap_update_bits_base+0x39/0x50) [<c0563add>] (regmap_update_bits_base) from [<c056fd39>] (max77620_pm_power_off+0x29/0x2c) [<c056fd39>] (max77620_pm_power_off) from [<c013bbdd>] (__do_sys_reboot+0xe9/0x170) [<c013bbdd>] (__do_sys_reboot) from [<c0101001>] (ret_fast_syscall+0x1/0x28) Exception stack(0xde907fa8 to 0xde907ff0) 7fa0: 00000000 00000000 fee1dead 28121969 4321fedc 00000000 7fc0: 00000000 00000000 00000000 00000058 00000000 00000000 00000000 00000000 7fe0: 0045adf0 bed9abb8 004444a0 b6c666d0 ---[ end trace bdd18f87595b1a5e ]--- The atomic transferring is implemented by enforcing PIO mode for the transfer and by polling interrupt status until transfer is completed or failed. Now system shuts down properly every time. Tested-by: Thierry Reding <treding@nvidia.com> Signed-off-by: Dmitry Osipenko <digetx@gmail.com> Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.