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

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Date:   Fri, 14 Apr 2023 12:55:43 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Robert Richter <rrichter@....com>
CC:     Ira Weiny <ira.weiny@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Terry Bowman <terry.bowman@....com>,
        <alison.schofield@...el.com>, <vishal.l.verma@...el.com>,
        <bwidawsk@...nel.org>, <dan.j.williams@...el.com>,
        <dave.jiang@...el.com>, <linux-cxl@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>,
        Oliver O'Halloran <oohall@...il.com>,
        "Mahesh J Salgaonkar" <mahesh@...ux.ibm.com>,
        <linuxppc-dev@...ts.ozlabs.org>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v3 6/6] PCI/AER: Unmask RCEC internal errors to enable
 RCH downstream port error handling

On Fri, 14 Apr 2023 13:21:37 +0200
Robert Richter <rrichter@....com> wrote:

> On 13.04.23 15:52:36, Ira Weiny wrote:
> > Jonathan Cameron wrote:  
> > > On Wed, 12 Apr 2023 16:29:01 -0500
> > > Bjorn Helgaas <helgaas@...nel.org> wrote:
> > >   
> > > > On Tue, Apr 11, 2023 at 01:03:02PM -0500, Terry Bowman wrote:  
> > > > > From: Robert Richter <rrichter@....com>
> > > > >   
> 
> > > > > +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/
> > 

Ah. I'd forgotten that thread. Thanks!

> > 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.  
> 
> The version I have ready after addressing Bjorn's comments is pretty
> much the same, apart from error checking of the read/writes.
> 
> From your patch proposed you will need it in aer.c too and we do not
> need to export it.

I think for the other components we'll want to call it from cxl_pci_ras_unmask()
so an export needed.

I also wonder if a more generic function would be better as seems likely
similar code will be needed for errors other than this pair.


> 
> This patch only enables it for (CXL) RCECs. You might want to extend
> this for CXL endpoints (and ports?) then.

Definitely.  We have the same limitation you are seeing.  No errors
without turning this on.

Jonathan



> 
> > 
> > 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.  
> 
> Thanks,
> 
> -Robert
> 
> > 
> > Ira