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Subject: Re: [PATCH v1 2/4] x86/pci: Re-use new dmi_get_bios_year() helper
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Jean Delvare <jdelvare@suse.de>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
        Linux PCI <linux-pci@vger.kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
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Date: Wed, 28 Feb 2018 21:34:21 +0200
In-Reply-To: <20180228202144.2ae8149f@endymion>
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On Wed, 2018-02-28 at 20:21 +0100, Jean Delvare wrote:
> On Wed, 28 Feb 2018 11:33:39 +0100, Rafael J. Wysocki wrote:
> > On Wed, Feb 28, 2018 at 11:29 AM, Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
> > > I would assume that no BIOS date is related to prehistoric
> > > firmwares and
> > >  using _CRS would sound weird on them.  
> > 
> > Careful here.
> > 
> > You seem to be assuming that the DMI information is always valid
> > and/or complete which is know to not be the case sometimes.
> 
> True. While the BIOS date is not the worst offender when it comes to
> broken DMI data, you must remember that the date comes as a string,
> and
> older SMBIOS specifications did not even recommend a specific format
> for that string. As a matter of fact, my collection of DMI tables
> includes a few creative samples like "Jul  7 2016" or "09-16-08" which
> the kernel fails to parse.
> 
> So the default behavior at the driver level shouldn't be based on what
> older systems are most likely to enjoy. The default behavior must be
> the safest option, regardless of the age of the system.

Yep.

And here is a very good question which path is more safer: use _CRS, or
not?

Rafael, do you know any consequences of not using _CRS for PCI on older
and newer machines?

-- 
Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy