ACK: [PATCH 0/1][B][D][E][Unstable] intel-lpss driver conflicts with write-combining MTRR region

[Seth Forshee]

On Fri, Sep 27, 2019 at 04:07:44PM +0800, AceLan Kao wrote:
> BugLink: https://bugs.launchpad.net/bugs/1845584
> 
> [Impact]
> The memory region intel-lpss-pci uses has been declared as
> write-combining
> [ 0.001728] 5 base 4000000000 mask 6000000000 write-combining
> This leads to the system hangs up during booting up.
> 
> This is a BIOS issue, but there are some platforms on the market and
> users are struggling on booting up the machines. So, we may have to
> fix this in the kernel.
> 
> [Fix]
> Tuowen Zhao(ztuowen at gmail.com)[1] provides a diff patch for intel-lpss
> driver to claim to use un-cacheable memory while calling
> __devm_ioremap(), and it works well. But it haven't been accepted by
> maintainer yet.
> 
> To avoid the potential impact on other machines, I add a quirk to list
> the machines which has the write-combining area in MTRR which overlaps
> with the address that intel-lpss uses, only the machines in the list
> pass DEVM_IOREMAP_UC to __devm_ioremap().
> 
> [Test]
> Verified on Dell XPS 13 7390 2-in-1
> 
> [Regression Potential]
> Low, without this patch, the machine even can't boot. And the quirk only
> for specific machines, so the modification won't affect other machines.
> 
> 1. https://bugzilla.kernel.org/show_bug.cgi?id=203485#c23

Impact limited to specific hw, positive testing.

Acked-by: Seth Forshee <seth.forshee at canonical.com>