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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Tue, 10 Dec 2019 09:11:43 +0100
Message-ID: <CAMuHMdXOnAO1h-uMf719muYhD4QEiVi7oMMeeGbuVd+mRrJcCA@mail.gmail.com>
Subject: Re: [PATCH v5 3/4] mfd: intel-lpss: use devm_ioremap_uc for MMIO
To:     Tuowen Zhao <ztuowen@gmail.com>
Cc:     Lee Jones <lee.jones@linaro.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        acelan.kao@canonical.com, "Luis R. Rodriguez" <mcgrof@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Christoph Hellwig <hch@lst.de>
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CC Christoph (ioremap() API cleanup)

On Thu, Oct 17, 2019 at 10:44 PM Tuowen Zhao <ztuowen@gmail.com> 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
> Cc: <stable@vger.kernel.org>
> 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>
> Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>
> ---
>  drivers/mfd/intel-lpss.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mfd/intel-lpss.c b/drivers/mfd/intel-lpss.c
> index bfe4ff337581..b0f0781a6b9c 100644
> --- a/drivers/mfd/intel-lpss.c
> +++ b/drivers/mfd/intel-lpss.c
> @@ -384,7 +384,7 @@ int intel_lpss_probe(struct device *dev,
>         if (!lpss)
>                 return -ENOMEM;
>
> -       lpss->priv = devm_ioremap(dev, info->mem->start + LPSS_PRIV_OFFSET,
> +       lpss->priv = devm_ioremap_uc(dev, info->mem->start + LPSS_PRIV_OFFSET,
>                                   LPSS_PRIV_SIZE);
>         if (!lpss->priv)
>                 return -ENOMEM;

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds