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

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Message-ID: <20201123195833.zeyhja6no6dkd32c@intel.com>
Date:   Mon, 23 Nov 2020 11:58:33 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Dan Williams <dan.j.williams@...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 20-11-23 11:32:33, Dan Williams wrote:
> 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

Currently in this path there are 2 general reasons for failure:
1. Driver internal problem, ENOMEM or some such.
2. Device problem (the memory device capability isn't present).

I think I'll return ENODEV for the former and ENXIO for the latter. If that
sounds good to everyone else.