Re: [PATCH v3 6/6] PCI/AER: Unmask RCEC internal errors to enable RCH downstream port error handling

[Ira Weiny <ira.weiny@intel.com>]

Jonathan Cameron wrote:
> On Wed, 12 Apr 2023 16:29:01 -0500
> Bjorn Helgaas <helgaas@kernel.org> wrote:
> 
> > On Tue, Apr 11, 2023 at 01:03:02PM -0500, Terry Bowman wrote:
> > > From: Robert Richter <rrichter@amd.com>
> > > 
> > > RCEC AER corrected and uncorrectable internal errors (CIE/UIE) are
> > > disabled by default.  
> > 
> > "Disabled by default" just means "the power-up state of CIE/UIC is
> > that they are masked", right?  It doesn't mean that Linux normally
> > masks them.
> > 
> > > [1][2] Enable them to receive CXL downstream port
> > > errors of a Restricted CXL Host (RCH).
> > > 
> > > [1] CXL 3.0 Spec, 12.2.1.1 - RCH Downstream Port Detected Errors
> > > [2] PCIe Base Spec 6.0, 7.8.4.3 Uncorrectable Error Mask Register,
> > >     7.8.4.6 Correctable Error Mask Register
> > > 
> > > Co-developed-by: Terry Bowman <terry.bowman@amd.com>
> > > Signed-off-by: Robert Richter <rrichter@amd.com>
> > > Signed-off-by: Terry Bowman <terry.bowman@amd.com>
> > > Cc: "Oliver O'Halloran" <oohall@gmail.com>
> > > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > > Cc: Mahesh J Salgaonkar <mahesh@linux.ibm.com>
> > > Cc: linuxppc-dev@lists.ozlabs.org
> > > Cc: linux-pci@vger.kernel.org
> > > ---
> > >  drivers/pci/pcie/aer.c | 73 ++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 73 insertions(+)
> > > 
> > > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> > > index 171a08fd8ebd..3973c731e11d 100644
> > > --- a/drivers/pci/pcie/aer.c
> > > +++ b/drivers/pci/pcie/aer.c
> > > @@ -1000,7 +1000,79 @@ static void cxl_handle_error(struct pci_dev *dev, struct aer_err_info *info)
> > >  		pcie_walk_rcec(dev, cxl_handle_error_iter, info);
> > >  }
> > >  
> > > +static bool cxl_error_is_native(struct pci_dev *dev)
> > > +{
> > > +	struct pci_host_bridge *host = pci_find_host_bridge(dev->bus);
> > > +
> > > +	if (pcie_ports_native)
> > > +		return true;
> > > +
> > > +	return host->native_aer && host->native_cxl_error;
> > > +}
> > > +
> > > +static int handles_cxl_error_iter(struct pci_dev *dev, void *data)
> > > +{
> > > +	int *handles_cxl = data;
> > > +
> > > +	*handles_cxl = is_cxl_mem_dev(dev) && cxl_error_is_native(dev);
> > > +
> > > +	return *handles_cxl;
> > > +}
> > > +
> > > +static bool handles_cxl_errors(struct pci_dev *rcec)
> > > +{
> > > +	int handles_cxl = 0;
> > > +
> > > +	if (!rcec->aer_cap)
> > > +		return false;
> > > +
> > > +	if (pci_pcie_type(rcec) == PCI_EXP_TYPE_RC_EC)
> > > +		pcie_walk_rcec(rcec, handles_cxl_error_iter, &handles_cxl);
> > > +
> > > +	return !!handles_cxl;
> > > +}
> > > +
> > > +static int __cxl_unmask_internal_errors(struct pci_dev *rcec)
> > > +{
> > > +	int aer, rc;
> > > +	u32 mask;
> > > +
> > > +	/*
> > > +	 * Internal errors are masked by default, unmask RCEC's here
> > > +	 * PCI6.0 7.8.4.3 Uncorrectable Error Mask Register (Offset 08h)
> > > +	 * PCI6.0 7.8.4.6 Correctable Error Mask Register (Offset 14h)
> > > +	 */  
> > 
> > Unmasking internal errors doesn't have anything specific to do with
> > CXL, so I don't think it should have "cxl" in the function name.
> > Maybe something like "pci_aer_unmask_internal_errors()".
> 
> This reminds me.  Not sure we resolved earlier discussion on changing
> the system wide policy to turn these on 
> https://lore.kernel.org/linux-cxl/20221229172731.GA611562@bhelgaas/
> which needs pretty much the same thing.
> 
> Ira, I think you were picking this one up?
> https://lore.kernel.org/linux-cxl/63e5fb533f304_13244829412@iweiny-mobl.notmuch/

After this discussion I posted an RFC to enable those errors.

https://lore.kernel.org/all/20230209-cxl-pci-aer-v1-1-f9a817fa4016@intel.com/

Unfortunately the prevailing opinion was that this was unsafe.  And no one
piped up with a reason to pursue the alternative of a pci core call to enable
them as needed.

So I abandoned the work.

I think the direction things where headed was to have a call like:

int pci_enable_pci_internal_errors(struct pci_dev *dev)
{
	int pos_cap_err;
	u32 reg;

	if (!pcie_aer_is_native(dev))
		return -EIO;

	pos_cap_err = dev->aer_cap;

	/* Unmask correctable and uncorrectable (non-fatal) internal errors */
	pci_read_config_dword(dev, pos_cap_err + PCI_ERR_COR_MASK, &reg);
	reg &= ~PCI_ERR_COR_INTERNAL;
	pci_write_config_dword(dev, pos_cap_err + PCI_ERR_COR_MASK, reg);
	
	pci_read_config_dword(dev, pos_cap_err + PCI_ERR_UNCOR_SEVER, &reg);
	reg &= ~PCI_ERR_UNC_INTN;
	pci_write_config_dword(dev, pos_cap_err + PCI_ERR_UNCOR_SEVER, reg);
	
	pci_read_config_dword(dev, pos_cap_err + PCI_ERR_UNCOR_MASK, &reg);
	reg &= ~PCI_ERR_UNC_INTN;
	pci_write_config_dword(dev, pos_cap_err + PCI_ERR_UNCOR_MASK, reg);

	return 0;
}

... and call this from the cxl code where it is needed.

Is this an acceptable direction?  Terry is welcome to steal the above from my
patch and throw it into the PCI core.

Looking at the current state of things I think cxl_pci_ras_unmask() may
actually be broken now without calling something like the above.  For that I
dropped the ball.

Ira