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

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Message-ID: <20201126181829.vy3was5c42ixtwxm@intel.com>
Date:   Thu, 26 Nov 2020 10:18:29 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Jon Masters <jcm@...masters.org>
Cc:     linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        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 20-11-26 01:05:56, Jon Masters 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?

Yeah, I think the message could be reworded, but it is dev_dbg, so I wasn't too
worried about the wording in the first place. I think it is a mistake in this
case for the spec to describe the intended purpose. If the expectation is for
platform firmware to use it, but there is no negotiation mechanism in place,
it's essentially useless.

> 
> 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.

Any reason not to articulate that here? Now that the spec is public, I don't see
any reason not to disclose that publicly.