Re: [PATCH v1 2/4] x86/pci: Re-use new dmi_get_bios_year() helper

From: Andy Shevchenko
Date: Wed Feb 28 2018 - 05:29:14 EST


On Mon, 2018-02-26 at 17:28 +0100, Jean Delvare wrote:

> > - if (dmi_get_date(DMI_BIOS_DATE, &year, NULL, NULL) && year
> > < 2008) {
> > - if (iomem_resource.end <= 0xffffffff)
> > - pci_use_crs = false;
> > - }
> > + if ((dmi_get_bios_year() < 2008) && (iomem_resource.end <=
> > 0xffffffff))
> > + pci_use_crs = false;
>
> You are changing the behavior here, when DMI does not provide a BIOS
> date. Beforehand, the test would fail and pci_use_crs would be left
> alone. After your change, dmi_get_bios_year() will return 0, and
> "0 < 2008" is true, so pci_use_crs is set to false.

Hmm... Indeed.

> I have no opinion on what this driver should do in such case,

I would assume that no BIOS date is related to prehistoric firmwares and
using _CRS would sound weird on them.

> but I
> certainly wouldn't expect a change of behavior from a "use a helper
> instead of open-coding" kind of patch.

Agree.

> I don't think you can safely assume that the code calling
> dmi_get_bios_year() will always do the right thing when 0 is being
> returned. It's up to the calling code to decide what the default
> behavior should be.

That's correct.

--
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy