Re: [PATCH 03/14] cxl/mem: Find device capabilities

[Dan Williams]

On Mon, Feb 1, 2021 at 1:51 PM David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> On Mon, 1 Feb 2021, Ben Widawsky wrote:
>
> > On 21-01-30 15:51:49, David Rientjes wrote:
> > > On Fri, 29 Jan 2021, Ben Widawsky wrote:
> > >
> > > > +static int cxl_mem_setup_mailbox(struct cxl_mem *cxlm)
> > > > +{
> > > > + const int cap = cxl_read_mbox_reg32(cxlm, CXLDEV_MB_CAPS_OFFSET);
> > > > +
> > > > + cxlm->mbox.payload_size =
> > > > +         1 << CXL_GET_FIELD(cap, CXLDEV_MB_CAP_PAYLOAD_SIZE);
> > > > +
> > > > + /* 8.2.8.4.3 */
> > > > + if (cxlm->mbox.payload_size < 256) {
> > > > +         dev_err(&cxlm->pdev->dev, "Mailbox is too small (%zub)",
> > > > +                 cxlm->mbox.payload_size);
> > > > +         return -ENXIO;
> > > > + }
> > >
> > > Any reason not to check cxlm->mbox.payload_size > (1 << 20) as well and
> > > return ENXIO if true?
> >
> > If some crazy vendor wanted to ship a mailbox larger than 1M, why should the
> > driver not allow it?
> >
>
> Because the spec disallows it :)

Unless it causes an operational failure in practice I'd go with the
Robustness Principle and be liberal in accepting hardware geometries.