Re: [PATCH v2 1/1] PCI: X-Gene: Disable Configuration Request Retry Status for X-Gene v1 PCIe

[Bjorn Helgaas <bhelgaas@google.com>]

On Fri, Jun 12, 2015 at 05:35:57PM -0700, Duc Dang wrote:
> X-Gene v1 PCIe controller has a bug in Configuration Request Retry
> Status (CRS) logic:
>   When CPU tries to read Vendor ID and Device ID of not-existed
>   remote device, the controller returns 0xFFFF0001 instead of
>   0xFFFFFFFF; this will add significant delay in boot time as
>   pci_bus_read_dev_vendor_id will wait for 60 seconds before
>   giving up.
> 
> So for X-Gene v1 PCIe controllers, disable CRS capability
> advertisement by clearing CRS Software Visibility bit before
> returning the Root Capability value to the callers. This is done
> by implementing X-Gene PCIe specific xgene_pcie_config_read32 for
> CFG read accesses to replace the generic default pci_generic_config_read32
> function.
> 
> v2 changes:
>         Use pci_generic_config_read32 to implement xgene_pcie_config_read32
> 
> Signed-off-by: Duc Dang <dhdang@apm.com>
> Tested-by: Ian Campbell <ian.campbell@citrix.com>
> Tested-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>

I'd like to merge this (as amended below) for v4.2.  But I'm looking for an
ack from Tanmay, and I'm still waiting for the second patch to remove the
link_up test.

Bjorn


commit 49ac8c566d7a37f9f295e1fd4fbdd96517f22d55
Author: Duc Dang <dhdang@apm.com>
Date:   Fri Jun 12 17:35:57 2015 -0700

    PCI: xgene: Disable Configuration Request Retry Status for v1 silicon
    
    When a CPU reads the Vendor and Device ID of a non-existent device, the
    controller should fabricate return data of 0xFFFFFFFF.  Configuration
    Request Retry Status (CRS) is not applicable in this case because the
    device doesn't exist at all.
    
    The X-Gene v1 PCIe controller has a bug in the CRS logic such that when CRS
    is enabled, it fabricates return data of 0xFFFF0001 for this case, which
    means "the device exists but is not ready."  That causes the PCI core to
    retry the read until it times out after 60 seconds.
    
    Disable CRS capability advertisement by clearing the CRS Software
    Visibility bit in the Root Capabilities Register.
    
    [bhelgaas: changelog and comment]
    Tested-by: Ian Campbell <ian.campbell@citrix.com>
    Tested-by: Marcin Juszkiewicz <mjuszkiewicz@redhat.com>
    Signed-off-by: Duc Dang <dhdang@apm.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/drivers/pci/host/pci-xgene.c b/drivers/pci/host/pci-xgene.c
index 3e5a636..70af714 100644
--- a/drivers/pci/host/pci-xgene.c
+++ b/drivers/pci/host/pci-xgene.c
@@ -59,6 +59,12 @@
 #define SZ_1T				(SZ_1G*1024ULL)
 #define PIPE_PHY_RATE_RD(src)		((0xc000 & (u32)(src)) >> 0xe)
 
+#define ROOT_CAP_AND_CTRL		0x5C
+
+/* PCIe IP version */
+#define XGENE_PCIE_IP_VER_UNKN		0
+#define XGENE_PCIE_IP_VER_1		1
+
 struct xgene_pcie_port {
 	struct device_node	*node;
 	struct device		*dev;
@@ -67,6 +73,7 @@ struct xgene_pcie_port {
 	void __iomem		*cfg_base;
 	unsigned long		cfg_addr;
 	bool			link_up;
+	u32			version;
 };
 
 static inline u32 pcie_bar_low_val(u32 addr, u32 flags)
@@ -140,9 +147,37 @@ static void __iomem *xgene_pcie_map_bus(struct pci_bus *bus, unsigned int devfn,
 	return xgene_pcie_get_cfg_base(bus) + offset;
 }
 
+static int xgene_pcie_config_read32(struct pci_bus *bus, unsigned int devfn,
+				    int where, int size, u32 *val)
+{
+	struct xgene_pcie_port *port = bus->sysdata;
+
+	if (pci_generic_config_read32(bus, devfn, where & ~0x3, 4, val) !=
+	    PCIBIOS_SUCCESSFUL)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
+	/*
+	 * The v1 controller has a bug in its Configuration Request
+	 * Retry Status (CRS) logic: when CRS is enabled and we read the
+	 * Vendor and Device ID of a non-existent device, the controller
+	 * fabricates return data of 0xFFFF0001 ("device exists but is not
+	 * ready") instead of 0xFFFFFFFF ("device does not exist").  This
+	 * causes the PCI core to retry the read until it times out.
+	 * Avoid this by not claiming to support CRS.
+	 */
+	if (pci_is_root_bus(bus) && (port->version == XGENE_PCIE_IP_VER_1) &&
+	    ((where & ~0x3) == ROOT_CAP_AND_CTRL))
+		*val &= ~(PCI_EXP_RTCAP_CRSVIS << 16);
+
+	if (size <= 2)
+		*val = (*val >> (8 * (where & 3))) & ((1 << (size * 8)) - 1);
+
+	return PCIBIOS_SUCCESSFUL;
+}
+
 static struct pci_ops xgene_pcie_ops = {
 	.map_bus = xgene_pcie_map_bus,
-	.read = pci_generic_config_read32,
+	.read = xgene_pcie_config_read32,
 	.write = pci_generic_config_write32,
 };
 
@@ -500,6 +535,10 @@ static int xgene_pcie_probe_bridge(struct platform_device *pdev)
 	port->node = of_node_get(pdev->dev.of_node);
 	port->dev = &pdev->dev;
 
+	port->version = XGENE_PCIE_IP_VER_UNKN;
+	if (of_device_is_compatible(port->node, "apm,xgene-pcie"))
+		port->version = XGENE_PCIE_IP_VER_1;
+
 	ret = xgene_pcie_map_reg(port, pdev);
 	if (ret)
 		return ret;