linux-kernel - Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry

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Message-ID: <87zheg93io.fsf@x220.int.ebiederm.org>
Date:   Tue, 21 Jan 2020 10:29:35 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Jean Delvare <jdelvare@...e.de>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dave Young <dyoung@...hat.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v1 2/2] firmware: dmi_scan: Pass dmi_entry_point to kexec'ed kernel

Jean Delvare <jdelvare@...e.de> writes:

> On Mon, 20 Jan 2020 23:55:43 +0200, Andy Shevchenko wrote:
>> On Mon, Jan 20, 2020 at 11:44 PM Jean Delvare <jdelvare@...e.de> wrote:
>> >
>> > On Mon, 20 Jan 2020 10:04:04 -0600, Eric W. Biederman wrote:  
>> > > Second.  I looked at your test results and they don't directly make
>> > > sense.  dmidecode bypasses the kernel completely or it did last time
>> > > I looked so I don't know why you would be using that to test if
>> > > something in the kernel is working.  
>> >
>> > That must have been long ago. A recent version of dmidecode (>= 3.0)
>> > running on a recent kernel  
>> > (>= d7f96f97c4031fa4ffdb7801f9aae23e96170a6f, v4.2) will read the DMI  
>> > data from /sys/firmware/dmi/tables, so it is very much relying on the
>> > kernel doing the right thing. If not, it will still try to fallback to
>> > reading from /dev/mem directly on certain architectures. You can force
>> > that old method with --no-sysfs.
>> >
>> > Hope that helps,  
>> 
>> I don't understand how it possible can help for in-kernel code, like
>> DMI quirks in a drivers.
>
> OK, just ignore me then, probably I misunderstood the point made by
> Eric.

No.  I just haven't dived into this area of code in a long time.

It seems a little indirect to use dmidecode as the test to see if the
kernel has the pointer to the dmitables, but with the knowledge you
provided it seems like a perfectly valid test.

Eric