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e479187748
Some buggy BIOS-es bring up the touchscreen-controller in a stuck state where it blocks the I2C bus. Specifically this happens on the Jumper EZpad 7 tablet model. After much poking at this problem I have found that the following steps are necessary to unstuck the chip / bus: 1. Turn off the Silead chip. 2. Try to do an I2C transfer with the chip, this will fail in response to which the I2C-bus-driver will call: i2c_recover_bus() which will unstuck the I2C-bus. Note the unstuck-ing of the I2C bus only works if we first drop the chip of the bus by turning it off. 3. Turn the chip back on. On the x86/ACPI systems were this problem is seen, step 1. and 3. require making ACPI calls and dealing with ACPI Power Resources. This commit adds a workaround which runtime-suspends the chip to turn it off, leaving it up to the ACPI subsystem to deal with all the ACPI specific details. There is no good way to detect this bug, so the workaround gets activated by a new "silead,stuck-controller-bug" boolean device-property. Since this is only used on x86/ACPI, this will be set by model specific device-props set by drivers/platform/x86/touchscreen_dmi.c. Therefor this new device-property is not documented in the DT-bindings. Dmesg will contain the following messages on systems where the workaround is activated: [ 54.309029] silead_ts i2c-MSSL1680:00: [Firmware Bug]: Stuck I2C bus: please ignore the next 'controller timed out' error [ 55.373593] i2c_designware 808622C1:04: controller timed out [ 55.582186] silead_ts i2c-MSSL1680:00: Silead chip ID: 0x80360000 Signed-off-by: Hans de Goede <hdegoede@redhat.com> Link: https://lore.kernel.org/r/20210405202745.16777-1-hdegoede@redhat.com Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> |
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| kernel | ||
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| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
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| README | ||
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.