cxl: Drop commands if the PCI channel is not in normal state

If the PCI channel has gone down, don't attempt to poke the hardware.

We need to guard every time cxl_whatever_(read|write) is called. This
is because a call to those functions will dereference an offset into an
mmio register, and the mmio mappings get invalidated in the EEH
teardown.

Check in the read/write functions in the header.
We give them the same semantics as usual PCI operations:
 - a write to a channel that is down is ignored.
 - a read from a channel that is down returns all fs.

Also, we try to access the MMIO space of a vPHB device as part of the
PCI disable path. Because that's a read that bypasses most of our usual
checks, we handle it explicitly.

As far as user visible warnings go:
 - Check link state in file ops, return -EIO if down.
 - Be reasonably quiet if there's an error in a teardown path,
   or when we already know the hardware is going down.
 - Throw a big WARN if someone tries to start a CXL operation
   while the card is down. This gives a useful stacktrace for
   debugging whatever is doing that.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 26 insertions, 0 deletions

diff --git a/drivers/misc/cxl/vphb.c b/drivers/misc/cxl/vphb.c
index 2eba002b580b..2930911c1e42 100644
--- a/drivers/misc/cxl/vphb.c
+++ b/drivers/misc/cxl/vphb.c
@@ -138,6 +138,26 @@ static int cxl_pcie_config_info(struct pci_bus *bus, unsigned int devfn,
 	return 0;
 }
 
+
+static inline bool cxl_config_link_ok(struct pci_bus *bus)
+{
+	struct pci_controller *phb;
+	struct cxl_afu *afu;
+
+	/* Config space IO is based on phb->cfg_addr, which is based on
+	 * afu_desc_mmio. This isn't safe to read/write when the link
+	 * goes down, as EEH tears down MMIO space.
+	 *
+	 * Check if the link is OK before proceeding.
+	 */
+
+	phb = pci_bus_to_host(bus);
+	if (phb == NULL)
+		return false;
+	afu = (struct cxl_afu *)phb->private_data;
+	return cxl_adapter_link_ok(afu->adapter);
+}
+
 static int cxl_pcie_read_config(struct pci_bus *bus, unsigned int devfn,
 				int offset, int len, u32 *val)
 {
@@ -150,6 +170,9 @@ static int cxl_pcie_read_config(struct pci_bus *bus, unsigned int devfn,
 	if (rc)
 		return rc;
 
+	if (!cxl_config_link_ok(bus))
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
 	/* Can only read 32 bits */
 	*val = (in_le32(ioaddr) >> shift) & mask;
 	return PCIBIOS_SUCCESSFUL;
@@ -167,6 +190,9 @@ static int cxl_pcie_write_config(struct pci_bus *bus, unsigned int devfn,
 	if (rc)
 		return rc;
 
+	if (!cxl_config_link_ok(bus))
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
 	/* Can only write 32 bits so do read-modify-write */
 	mask <<= shift;
 	val <<= shift;