Re: Fix for Dell P57G touchpad found, need advice on patch

[Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>]

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Hi Pavel,

On Thu, Sep 10, 2015 at 11:11:41PM -0700, Pavel Roskin wrote:
> Hi!

Thanks for this detailed info. Adding Mika to CC who is an expert of
this driver. Mika, maybe we should add you to MAINTAINERS, too?

> I'm using Dell Inspiron 13, model P57G. It has a problem with the
> touchpad under Linux. Approximately half of the time, the touchpad is
> not working at all - the mouse cursor is not moving. In this case,
> there are error messages written to the kernel log every second:
> 
> [   53.127339] i2c_designware INT3433:00: controller timed out
> [   54.219336] i2c_designware INT3433:00: controller timed out
> [   55.311346] i2c_designware INT3433:00: controller timed out
> [   56.403326] i2c_designware INT3433:00: controller timed out
> 
> There is a simple fix - blacklist the driver
> (i2c_designware_platform). In this case, the touchpad words as a mouse
> and used IRQ 12. Googling for "blackist i2c_designware_platform" shows
> that I'm not the one using that approach.
> 
> I started looking at the driver in git. A patch by Romain Baeriswyl
> applied on 2014-08-20 adds support for the "standard" mode with the
> 100kHz clock, as opposed to the 400kHz "fast" mode. Unfortunately,
> that patch only affects OpenFirmware systems, and I have ACPI. As soon
> as I set the clock to 100kHz, the touchpad started working every time.
> 
> One fix would be to have a module parameter to force slower clock. It
> would still require users to deal with modprobe, so it's not optimal.
> 
> I noticed that dev->get_clk_rate_khz(dev) returns 100000, but that
> would be 100000kHz = 100MHz. Not sure is somebody confused the units
> or it's the correct clock.
> 
> Considering that I have no other systems to test, what would be the
> best approach? Set the clock to 100kHz for INT3433? Recognize Dell
> P57G system specifically? How? Preserve the original clock by reading
> the DW_IC_CON register and keeping some bits?

Note: The driver has been using 400kHz from its beginning. However,
100kHz is usually a better default for I2C busses. I wonder if we should
take the risk of a performance regression in favour of a sane and
working default?

Regards,

   Wolfram


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