linux-kernel - Re: [PATCH v1 2/4] x86/pci: Re-use new dmi_get_bios

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Message-ID: <1519846461.10722.309.camel@linux.intel.com>
Date:   Wed, 28 Feb 2018 21:34:21 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Jean Delvare <jdelvare@...e.de>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/4] x86/pci: Re-use new dmi_get_bios_year() helper

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@...ux.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@...ux.intel.com>
Intel Finland Oy