Re: `ucsi_acpi: probe of USBC000:00 failed with error -12` on Dell XPS 13 9360/9370

[Rafael J. Wysocki]

On Fri, May 18, 2018 at 5:15 PM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, May 18, 2018 at 06:08:24PM +0300, Heikki Krogerus wrote:
>>
>> Rafael, the problem here with these Dell laptops is that a memory page
>> that is used as a mailbox for special communication between EC FW and
>> OS (called UCSI mailbox) should be in uncached memory, but the memory
>> is marked as cached.

Well, why don't we map it as uncached, then?

>> I'm actually not even sure if the cache mode is something that is set
>> based on information from ACPI tables, or is it something that the
>> BIOS handles separately?

We map the ACPI tables as cached as a rule, so that may be the reason.

>> If it's information coming from ACPI tables, can we help pin point the
>> place the BIOS guys at Dell should fix?

I'm not sure where this particular piece comes from.

> Given that Windows works with this same set of ACPI tables, perhaps the
> requirement isn't that this memory location be uncached?
>
> We shouldn't have to fix up ACPI tables just for Linux, we've been down
> that path before :(

Yes, pretty much.

Thanks,
Rafael