Re: [PATCH v3 1/3] cxl/pci: Fix appropriate checking for _OSC while handling CXL RAS registers

[Smita Koralahalli]

On 8/16/2023 11:06 AM, Dave Jiang wrote:
> On 8/4/23 05:09, Jonathan Cameron wrote:
> > On Thu, 3 Aug 2023 23:01:27 +0000
> > Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx> wrote:
> >
> > > According to Section 9.17.2, Table 9-26 of CXL Specification [1], owner
> > > of AER should also own CXL Protocol Error Management as there is no
> > > explicit control of CXL Protocol error. And the CXL RAS Cap registers
> > > reported on Protocol errors should check for AER _OSC rather than CXL
> > > Memory Error Reporting Control _OSC.
> > >
> > > The CXL Memory Error Reporting Control _OSC specifically highlights
> > > handling Memory Error Logging and Signaling Enhancements. These kinds of
> > > errors are reported through a device's mailbox and can be managed
> > > independently from CXL Protocol Errors.
> > >
> > > This change fixes handling and reporting CXL Protocol Errors and RAS
> > > registers natively with native AER and FW-First CXL Memory Error 
> > > Reporting
> > > Control.
> > >
> > > [1] Compute Express Link (CXL) Specification, Revision 3.1, Aug 1 2022.
> > >
> > > Fixes: 248529edc86f ("cxl: add RAS status unmasking for CXL")
> > > Signed-off-by: Smita Koralahalli 
> > > <Smita.KoralahalliChannabasappa@xxxxxxx>
> > > Reviewed-by: Robert Richter <rrichter@xxxxxxx>
> >
> > I'd be tempted to add a comment on why this returns 0 rather than an
> > error.  I think that makes sense but it isn't immediately obvious from
> > the local context.
> >
> > Otherwise LGTM
> >
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>
> Echo Jonathan's comment.
>
> Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>

Yes, and Dan is probably against returning error code.
https://lore.kernel.org/all/64d1b3e78629f_5ea6e2944@xxxxxxxxxxxxxxxxxxxxxxxxx.notmuch/

But I think returning zero is required as we don't want to interfere 
with cxl device access when operating in native cxl memory error 
reporting. Returning error code will basically fail cxl_pci_probe() and 
thus fail to create a cxl device node.

I was thinking a single line comment as: "Return zero to not block the 
communication with the cxl device when in native memory error reporting 
mode".

Agree? Or anything more that needs to be added?

Thanks,
Smita
> > > ---
> > > v2:
> > >     Added fixes tag.
> > >     Included what the patch fixes in commit message.
> > > v3:
> > >     Added "Reviewed-by" tag.
> > > ---
> > >   drivers/cxl/pci.c | 6 +++---
> > >   1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/cxl/pci.c b/drivers/cxl/pci.c
> > > index 1cb1494c28fe..2323169b6e5f 100644
> > > --- a/drivers/cxl/pci.c
> > > +++ b/drivers/cxl/pci.c
> > > @@ -541,9 +541,9 @@ static int cxl_pci_ras_unmask(struct pci_dev *pdev)
> > >           return 0;
> > >       }
> > > -    /* BIOS has CXL error control */
> > > -    if (!host_bridge->native_cxl_error)
> > > -        return -ENXIO;
> > > +    /* BIOS has PCIe AER error control */
> > > +    if (!host_bridge->native_aer)
> > > +        return 0;
> > >       rc = pcie_capability_read_word(pdev, PCI_EXP_DEVCTL, &cap);
> > >       if (rc)