linux-kernel - Re: [RFC PATCH 4/9] cxl/mem: Map memory device registers

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Message-ID: <CAPcyv4jJpvLErK8vBW-D2ZQASU0iJqFLRr7yDXB0kfGPrmi6xw@mail.gmail.com>
Date:   Mon, 23 Nov 2020 11:32:33 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, 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 4/9] cxl/mem: Map memory device registers

On Mon, Nov 23, 2020 at 11:20 AM Ben Widawsky <ben.widawsky@...el.com> wrote:
[..]
> > -ENXIO is fine with me.  I just don't see it as often so I don't
> > really know what it is.
> >
> > Bjorn
>
> Dan, Bjorn, I did a fairly randomized look at various probe functions and ENODEV
> seems to be more common. My sort of historical use has been
> - ENODEV: General, couldn't establish device presence
> - ENXIO: Device was there but something is totally misconfigured
> - E*: A matching errno for exactly what went wrong
>
> My question though is, would it be useful to propagate the error up through
> probe?

The error from probe becomes the modprobe exit code, or the write to
the 'bind' attribute errno. So, it's a choice between "No such device
or address", or "No such device". The "or address" mention makes a
small bit more sense to me since the device is obviously present as it
is visible in lspci, but either error code clearly indicates a driver
problem so ENODEV is fine.

For the other error codes I think it would be confusing to return
something like EINVAL from probe as that would be mistaken as an
invalid argument to the modprobe without stracing to see that it came
from the result of a sysfs write