linux-kernel - Re: [RFC PATCH 5/9] cxl/mem: Find device capabilities

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Message-ID: <CAPcyv4hYR8Ty2vq6kfG6_h6XRQPv2=-x4S0DgyzAykgx0TWzog@mail.gmail.com>
Date:   Thu, 3 Dec 2020 23:35:51 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jon Masters <jcm@...masters.org>
Cc:     Ben Widawsky <ben.widawsky@...el.com>, linux-cxl@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH 5/9] cxl/mem: Find device capabilities

On Wed, Nov 25, 2020 at 10:06 PM Jon Masters <jcm@...masters.org> wrote:
>
> On 11/11/20 12:43 AM, Ben Widawsky wrote:
>
> > +             case CXL_CAPABILITIES_CAP_ID_SECONDARY_MAILBOX:
> > +                     dev_dbg(&cxlm->pdev->dev,
> > +                                "found UNSUPPORTED Secondary Mailbox capability\n");
>
> Per spec, the secondary mailbox is intended for use by platform
> firmware, so Linux should never be using it anyway. Maybe that message
> is slightly misleading?
>
> Jon.
>
> P.S. Related - I've severe doubts about the mailbox approach being
> proposed by CXL and have begun to push back through the spec org.

The more Linux software voices the better. At the same time the spec
is released so we're into xkcd territory [1] of what the driver will
be expected to support for any future improvements.

[1]: https://xkcd.com/927/