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Date:   Thu, 10 Oct 2019 12:08:23 +0000
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Tuowen Zhao <ztuowen@gmail.com>
Cc:     lee.jones@linaro.org, linux-kernel@vger.kernel.org,
        andriy.shevchenko@linux.intel.com, mika.westerberg@linux.intel.com,
        acelan.kao@canonical.com, bhelgaas@google.com,
        kai.heng.feng@canonical.com
Subject: Re: [PATCH v3 2/2] mfd: intel-lpss: use devm_ioremap_uc for MMIO
Message-ID: <20191010120823.GD16384@42.do-not-panic.com>
References: <20191010030335.204974-1-ztuowen@gmail.com>
 <20191010030335.204974-2-ztuowen@gmail.com>
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On Wed, Oct 09, 2019 at 09:03:35PM -0600, Tuowen Zhao wrote:
> Some BIOS erroneously specifies write-combining BAR for intel-lpss-pci
> in MTRR. This will cause the system to hang during boot. If possible,
> this bug could be corrected with a firmware update.
> 
> This patch use devm_ioremap_uc to overwrite/ignore the MTRR settings
> by forcing the use of strongly uncachable pages for intel-lpss.
> 
> The BIOS bug is present on Dell XPS 13 7390 2-in-1:
> 
> [    0.001734]   5 base 4000000000 mask 6000000000 write-combining
> 
> 4000000000-7fffffffff : PCI Bus 0000:00
>   4000000000-400fffffff : 0000:00:02.0 (i915)
>   4010000000-4010000fff : 0000:00:15.0 (intel-lpss-pci)
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=203485
> Tested-by: AceLan Kao <acelan.kao@canonical.com>
> Signed-off-by: Tuowen Zhao <ztuowen@gmail.com>
> Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

I think you'll want to Cc stable for this, as well as the last patch.
LTS kernels with the ioremap_uc will be able to leverage the fix.

  Luis