linux-kernel - [PATCH v2 4/5] cxl/pci: Forward RCH downstream port-detected errors to the CXL.mem dev handler

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Date:   Thu, 23 Mar 2023 16:38:07 -0500
From:   Terry Bowman <terry.bowman@....com>
To:     <terry.bowman@....com>, <alison.schofield@...el.com>,
        <vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
        <bwidawsk@...nel.org>, <dan.j.williams@...el.com>,
        <dave.jiang@...el.com>, <Jonathan.Cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>, <rrichter@....com>
CC:     <linux-kernel@...r.kernel.org>, <bhelgaas@...gle.com>
Subject: [PATCH v2 4/5] cxl/pci: Forward RCH downstream port-detected errors to the CXL.mem dev handler

From: Robert Richter <rrichter@....com>

In RCD mode a CXL device (RCD) is exposed as an RCiEP, but CXL
downstream and upstream ports are not enumerated and not visible in
the PCIe hierarchy. Protocol and link errors are sent to an RCEC.

Now, RCH downstream port-detected errors are signaled as internal AER
errors (UIE/CIE) with the RCEC's source ID. A CXL handler must then
inspect the error status in various CXL registers residing in the
dport's component register space (CXL RAS cap) or the dport's RCRB
(AER ext cap). [1]

This patch connects errors showing up in the RCEC's error handler with
the CXL subsystem. Implement this by forwarding the error to all CXL
devices below the RCEC. Since the entire CXL device is controlled only
using PCIe Configuration Space of device 0, Function 0, only pass it
there [2]. These devices have the Memory Device class code set
(PCI_CLASS_MEMORY_CXL, 502h) and the existing cxl_pci driver can
implement the handler. The CXL device driver is then responsible to
enable error reporting in the RCEC's AER cap (esp. CIE and UIE) and to
inspect the dport's CXL registers in addition (CXL RAS cap and AER ext
cap).

The reason for choosing this implementation is that a CXL RCEC device
is bound to the AER port driver, but the driver does not allow it to
register a custom specific handler to support CXL. Connecting the RCEC
hard-wired with a CXL handler does not work, as the CXL subsystem
might not be present all the time. The alternative to add an
implementation to the portdrv to allow the registration of a custom
RCEC error handler isn't worth doing it as CXL would be its only user.
Instead, just check for an CXL RCEC and pass it down to the connected
CXL device's error handler.

[1] CXL 3.0 spec, 12.2.1.1 RCH Downstream Port-detected Errors
[2] CXL 3.0 spec, 8.1.3 PCIe DVSEC for CXL Devices

Co-developed-by: Terry Bowman <terry.bowman@....com>
Signed-off-by: Terry Bowman <terry.bowman@....com>
Signed-off-by: Robert Richter <rrichter@....com>
Cc: "Oliver O'Halloran" <oohall@...il.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: linux-pci@...r.kernel.org
---
 drivers/pci/pcie/aer.c | 45 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
index 7f0f52d094a4..d250a4caa85a 100644
--- a/drivers/pci/pcie/aer.c
+++ b/drivers/pci/pcie/aer.c
@@ -943,6 +943,49 @@ static bool find_source_device(struct pci_dev *parent,
 	return true;
 }

+#if IS_ENABLED(CONFIG_CXL_PCI)
+
+static void handle_error_source(struct pci_dev *dev, struct aer_err_info *info);
+
+static int handle_cxl_error_iter(struct pci_dev *dev, void *data)
+{
+	struct aer_err_info *e_info = (struct aer_err_info *)data;
+
+	if (dev->devfn != PCI_DEVFN(0, 0))
+		return 0;
+
+	/* Right now there is only a CXL.mem driver */
+	if ((dev->class >> 8) != PCI_CLASS_MEMORY_CXL)
+		return 0;
+
+	/* pci_dev_put() in handle_error_source() */
+	dev = pci_dev_get(dev);
+	if (dev)
+		handle_error_source(dev, e_info);
+
+	return 0;
+}
+
+static bool is_internal_error(struct aer_err_info *info)
+{
+	if (info->severity == AER_CORRECTABLE)
+		return info->status & PCI_ERR_COR_INTERNAL;
+
+	return info->status & PCI_ERR_UNC_INTN;
+}
+
+static void handle_cxl_error(struct pci_dev *dev, struct aer_err_info *info)
+{
+	if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_EC &&
+	    is_internal_error(info))
+		pcie_walk_rcec(dev, handle_cxl_error_iter, info);
+}
+
+#else
+static inline void handle_cxl_error(struct pci_dev *dev,
+				    struct aer_err_info *info) { }
+#endif
+
 /**
  * handle_error_source - handle logging error into an event log
  * @dev: pointer to pci_dev data structure of error source device
@@ -954,6 +997,8 @@ static void handle_error_source(struct pci_dev *dev, struct aer_err_info *info)
 {
 	int aer = dev->aer_cap;

+	handle_cxl_error(dev, info);
+
 	if (info->severity == AER_CORRECTABLE) {
 		/*
 		 * Correctable error does not need software intervention.
-- 
2.34.1