linux-kernel - Re: [PATCH v3 1/3] cxl/pci: Fix appropriate checking for

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Date:   Wed, 16 Aug 2023 14:33:56 -0700
From:   Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To:     Dave Jiang <dave.jiang@...el.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-cxl@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        oohall@...il.com, Lukas Wunner <lukas@...ner.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Terry Bowman <terry.bowman@....com>,
        Robert Richter <rrichter@....com>
Subject: Re: [PATCH v3 1/3] cxl/pci: Fix appropriate checking for _OSC while
 handling CXL RAS registers

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@....com> 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@....com>
>>> Reviewed-by: Robert Richter <rrichter@....com>
>>
>> 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@...wei.com>
> 
> Echo Jonathan's comment.
> 
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>

Yes, and Dan is probably against returning error code.
https://lore.kernel.org/all/64d1b3e78629f_5ea6e2944@dwillia2-xfh.jf.intel.com.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)
>>