Re: [PATCH v5 3/4] mfd: intel-lpss: use devm_ioremap_uc for MMIO

[Roman Gilg]

On Thu, Oct 17, 2019 at 7:48 PM Tuowen Zhao <ztuowen@xxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> Tested-by: AceLan Kao <acelan.kao@xxxxxxxxxxxxx>
> Signed-off-by: Tuowen Zhao <ztuowen@xxxxxxxxx>
> Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Acked-for-MFD-by: Lee Jones <lee.jones@xxxxxxxxxx>
> ---
>  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;
> --
> 2.23.0
>

Tested this v5 series on an XPS 13 7390 2-in-1 with Manjaro/KDE
install and works fine there. Fixes hang during boot. Currently being
backported to 5.3 on that distro:
https://gitlab.manjaro.org/packages/core/linux53/commit/c00ddfb5

Tested-by: Roman Gilg <subdiff@xxxxxxxxx>