Re: [BUG] i2c: acpi: Dell XPS 17 9720 ELAN 04F3:311C touchpad (VEN_04F3) needs 100 kHz like DLL0945

[Mika Westerberg <mika.westerberg@linux.intel.com>]

Hi,

On Thu, Nov 12, 2026 at 02:18:35AM +0000, penhouse24@proton.me wrote:
> Hi Mika, 
> 
> 
> Tested on top of v7.4-rc2 (067c5c24cef2) on a Dell XPS 17 9720, BIOS 1.41.0, without the SSDT override.
> 
> The quirk is applied at boot.
> 
> I've been using my laptop all day and the touchpad lag has not come back so far including on AC power. On the unpatched kernel it returns as before.

Thanks for testing!

> Interestingly enough, I did use an off-brand AC charger for my laptop and the touchpad lag returned on the patched and unpatched Linux kernels AND Windows. When I used the Dell AC charger, the lag was gone on the patched kernel and Windows, but remained on the unpatched kernel. Perhaps the root cause of this problem, on Linux relative to Windows is that Windows aggressively filters noise without smoothing? Not sure, just a thought

Indeed it can very well be. Someone should really investigate this properly
by hooking I2C analyzer to the bus to see what is going on there. However,
that is not trivial to do with form factor devices.

> One question about the DMI match: does it need DMI_BIOS_VERSION? The VEN_04F3 ID check already makes the quirk stop applying if a future BIOS switches to a proper ACPI ID. The 400 kHz problem also seems to be in the touchpad itself, since the same 04F3:311C part is affected on the Precision 5560. Matching only on sys_vendor and product_name would also cover users on older BIOS versions, and any newer BIOS that still reports VEN_04F3.
> 
> Dell also ships the same BIOS image for the Precision 5770, so it likely exposes the same ID, though I can't test that model.

I agree we can drop the BIOS version. I will send the updated patch soon.