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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 30 Sep 2021 13:23:57 -0700
Message-ID: <CAPcyv4gZ=pm5GKV5q-QDqaVw+HAepiLdAokbcgqKooH-6bZcEg@mail.gmail.com>
Subject: Re: [PATCH v2 1/6] driver core: Move the "authorized" attribute from
 USB/Thunderbolt to core
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc:     Yehezkel Bernat <yehezkelshb@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Borislav Petkov <bp@alien8.de>, X86 ML <x86@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Andreas Noever <andreas.noever@gmail.com>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Michael Jamet <michael.jamet@intel.com>,
        "Rafael J . Wysocki" <rafael@kernel.org>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Jason Wang <jasowang@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        virtualization@lists.linux-foundation.org
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On Thu, Sep 30, 2021 at 12:50 PM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
>
>
> On 9/30/21 12:04 PM, Dan Williams wrote:
> >>> That's why it was highlighted in the changelog. Hopefully a
> >>> Thunderbolt developer can confirm if it is a non-issue.
> >>> Documentation/ABI/testing/sysfs-bus-thunderbolt does not seem to
> >>> answer this question about whether authorized_show and
> >>> authorized_store need to be symmetric.
> >> Apparently, Bolt does read it [1] and cares about it [2].
> > Ah, thank you!
> >
> > Yeah, looks like the conversion to bool was indeed too hopeful.
> >
>
> IIUC, the end result of value "2" in authorized sysfs is to just
> "authorize" or "de-authorize". In that case, can the user space
> driver adapt to this int->bool change? Just want to know the
> possibility.

ABIs are forever. The kernel has to uphold its contract to bolt that
it will return '2' and not '1' after '2' has been written.