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Re: [PATCH v3 1/2] PCI: iproc: Retry request when CRS returned from EP

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  Re: [PATCH v3 1/2] PCI: iproc: Retry request when CRS returned from  EP Bjorn Helgaas <helgaas@kernel.org> - 2017-06-20 00:40 +0200
    Re: [PATCH v3 1/2] PCI: iproc: Retry request when CRS returned from EP Oza Oza <oza.oza@broadcom.com> - 2017-06-20 14:50 +0200

#1670011 — Re: [PATCH v3 1/2] PCI: iproc: Retry request when CRS returned from EP

On Tue, Jun 13, 2017 at 09:58:22AM +0530, Oza Oza wrote:
> On Tue, Jun 13, 2017 at 5:00 AM, Bjorn Helgaas <helgaas@kernel.org> wrote:
> > Please wrap your changelogs to use 75 columns.  "git log" indents the
> > changelog by four spaces, so if your text is 75 wide, it will still
> > fit without wrapping.
> >
> > On Sun, Jun 11, 2017 at 09:35:37AM +0530, Oza Pawandeep wrote:
> >> For Configuration Requests only, following reset
> >> it is possible for a device to terminate the request
> >> but indicate that it is temporarily unable to process
> >> the Request, but will be able to process the Request
> >> in the future – in this case, the Configuration Request
> >> Retry Status 10 (CRS) Completion Status is used
> >
> > How does this relate to the CRS support we already have in the core,
> > e.g., pci_bus_read_dev_vendor_id()?  It looks like your root complex
> > already returns 0xffff0001 (CFG_RETRY_STATUS) in some cases.
> >
> > Also, per spec (PCIe r3.1, sec 2.3.2), CRS Software Visibility only
> > affects config reads of the Vendor ID, but you call
> > iproc_pcie_cfg_retry() for all config offsets.
> 
> Yes, as per Spec, CRS Software Visibility only affects config read of
> the Vendor ID.
> For config write or any other config read the Root must automatically
> re-issue configuration
> request again as a new request, and our PCIe RC fails to do so.

OK, if this is a workaround for a hardware defect, let's make that
explicit in the changelog (and probably a comment in the code, too).

I'm actually not sure the spec *requires* the CRS retries to be done
directly in hardware, so it's conceivable the hardware could be
working as designed.  But a comment would go a long way toward making
this understandable by differentiating it from the generic CRS
handling in the core.

Bjorn

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#1670734 — Re: [PATCH v3 1/2] PCI: iproc: Retry request when CRS returned from EP

On Tue, Jun 20, 2017 at 4:09 AM, Bjorn Helgaas <helgaas@kernel.org> wrote:
> On Tue, Jun 13, 2017 at 09:58:22AM +0530, Oza Oza wrote:
>> On Tue, Jun 13, 2017 at 5:00 AM, Bjorn Helgaas <helgaas@kernel.org> wrote:
>> > Please wrap your changelogs to use 75 columns.  "git log" indents the
>> > changelog by four spaces, so if your text is 75 wide, it will still
>> > fit without wrapping.
>> >
>> > On Sun, Jun 11, 2017 at 09:35:37AM +0530, Oza Pawandeep wrote:
>> >> For Configuration Requests only, following reset
>> >> it is possible for a device to terminate the request
>> >> but indicate that it is temporarily unable to process
>> >> the Request, but will be able to process the Request
>> >> in the future – in this case, the Configuration Request
>> >> Retry Status 10 (CRS) Completion Status is used
>> >
>> > How does this relate to the CRS support we already have in the core,
>> > e.g., pci_bus_read_dev_vendor_id()?  It looks like your root complex
>> > already returns 0xffff0001 (CFG_RETRY_STATUS) in some cases.
>> >
>> > Also, per spec (PCIe r3.1, sec 2.3.2), CRS Software Visibility only
>> > affects config reads of the Vendor ID, but you call
>> > iproc_pcie_cfg_retry() for all config offsets.
>>
>> Yes, as per Spec, CRS Software Visibility only affects config read of
>> the Vendor ID.
>> For config write or any other config read the Root must automatically
>> re-issue configuration
>> request again as a new request, and our PCIe RC fails to do so.
>
> OK, if this is a workaround for a hardware defect, let's make that
> explicit in the changelog (and probably a comment in the code, too).
>
> I'm actually not sure the spec *requires* the CRS retries to be done
> directly in hardware, so it's conceivable the hardware could be
> working as designed.  But a comment would go a long way toward making
> this understandable by differentiating it from the generic CRS
> handling in the core.
>
> Bjorn

Sure, I will update the commit message and also will add explicit
comment in the code.

Regards,
Oza.

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