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

Ben Widawsky
2020-11-23T19:20:58Z

On 20-11-16 18:23:21, Bjorn Helgaas wrote:
> On Mon, Nov 16, 2020 at 03:19:41PM -0800, Dan Williams wrote:
> > On Fri, Nov 13, 2020 at 5:12 PM Ben Widawsky <ben.widawsky@intel.com> wrote:
> > > On 20-11-13 12:17:32, Bjorn Helgaas wrote:
> > > > On Tue, Nov 10, 2020 at 09:43:51PM -0800, Ben Widawsky wrote:
>
> > > > > static int cxl_mem_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> > > > > {
> > > > > + struct cxl_mem *cxlm = ERR_PTR(-ENXIO);
> > > > > struct device *dev = &pdev->dev;
> > > > > - struct cxl_mem *cxlm;
> > > >
> > > > The order was better before ("dev", then "clxm"). Oh, I suppose this
> > > > is a "reverse Christmas tree" thing.
> > > >
> > >
> > > I don't actually care either way as long as it's consistent. I tend to do
> > > reverse Christmas tree for no particular reason.
> >
> > Yeah, reverse Christmas tree for no particular reason.
>
> FWIW, the usual drivers/pci style is to order the decls in the order
> the variables are used in the code. But this isn't drivers/pci, so
> it's up to you. I only noticed because changing the order made the
> diff bigger than it needed to be.
>
> > > > I think this would be easier to read if cxl_mem_create() returned NULL
> > > > on failure (it prints error messages and we throw away
> > > > -ENXIO/-ENOMEM distinction here anyway) so you could do:
> > > >
> > > > struct cxl_mem *cxlm = NULL;
> > > >
> > > > for (...) {
> > > > if (...) {
> > > > cxlm = cxl_mem_create(pdev, reg_lo, reg_hi);
> > > > break;
> > > > }
> > > > }
> > > >
> > > > if (!cxlm)
> > > > return -ENXIO; /* -ENODEV might be more natural? */
> > > >
> > >
> > > I agree on both counts. Both of these came from Dan, so I will let him explain.
> >
> > I'm not attached to differentiating -ENOMEM from -ENXIO and am ok to
> > drop the ERR_PTR() return. I do tend to use -ENXIO for failure to
> > perform an initialization action vs failure to even find the device,
> > but if -ENODEV seems more idiomatic to Bjorn, I won't argue.
>
> -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?