Re: [PATCH v2] i2c: acpi: Force bus speed to 400KHz if a Silead touchscreen is present

[Wolfram Sang <wsa@the-dreams.de>]

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On Wed, Nov 13, 2019 at 07:29:38PM +0100, Hans de Goede wrote:
> Many cheap devices use Silead touchscreen controllers. Testing has shown
> repeatedly that these touchscreen controllers work fine at 400KHz, but for
> unknown reasons do not work properly at 100KHz. This has been seen on
> both ARM and x86 devices using totally different i2c controllers.
> 
> On some devices the ACPI tables list another device at the same I2C-bus
> as only being capable of 100KHz, testing has shown that these other
> devices work fine at 400KHz (as can be expected of any recent I2C hw).
> 
> This commit makes i2c_acpi_find_bus_speed() always return 400KHz if a
> Silead touchscreen controller is present, fixing the touchscreen not
> working on devices which ACPI tables' wrongly list another device on the
> same bus as only being capable of 100KHz.
> 
> Specifically this fixes the touchscreen on the Jumper EZpad 6 m4 not
> working.
> 
> Reported-and-tested-by: youling 257 <youling257@gmail.com>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Stable material, I'd say?

> +			dev_warn(dev, FW_BUG "DSDT wrongly sets I2C bus speed to %d, forcing it to %d\n",
> +				 lookup.min_speed, lookup.force_speed);

I have not a strong opinion here. However, does the DSDT really wrongly
set a bus speed when it is the touchscreen controller which cannot
handle lower speeds and other devies are specified to run at 100kHz?


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