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

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Message-ID: <CAJZ5v0hbpgvvmvCvxEVGed8VcOXoO1TTEXK9zsXxCGP4wLqrZA@mail.gmail.com>
Date:   Fri, 18 May 2018 22:04:02 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Paul Menzel <pmenzel+linux-usb@...gen.mpg.de>,
        Mario Limonciello <mario.limonciello@...l.com>,
        "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" 
        <linux-usb@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thorsten Leemhuis <linux@...mhuis.info>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: `ucsi_acpi: probe of USBC000:00 failed with error -12` on Dell
 XPS 13 9360/9370

On Fri, May 18, 2018 at 5:15 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> 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