[Xen-devel] [PATCH RFC 4/4] ns16550: enable use of PCI MSI

["Jan Beulich" <JBeulich@xxxxxxxx>]

Which, on x86, requires fiddling with the INTx bit in PCI config space,
since for internally used MSI we can't delegate this to Dom0.

ns16550_init_postirq() also needs (benign) re-ordering of its
operations.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC reason: No interrupts occur for an unknown reason (presumably
            broken hardware/firmware on the device I have).

--- a/xen/arch/x86/msi.c
+++ b/xen/arch/x86/msi.c
@@ -738,6 +738,16 @@ static int msi_capability_init(struct pc
 
     *desc = entry;
     /* Restore the original MSI enabled bits  */
+    if ( !hardware_domain )
+    {
+        /*
+         * Except for internal requests (before Dom0 starts), in which case
+         * we rather need to behave "normally", i.e. not follow the split
+         * brain model where Dom0 actually enables MSI (and disables INTx).
+         */
+        pci_intx(dev, 0);
+        control |= PCI_MSI_FLAGS_ENABLE;
+    }
     pci_conf_write16(seg, bus, slot, func, msi_control_reg(pos), control);
 
     return 0;
@@ -1071,6 +1081,8 @@ static void __pci_disable_msi(struct msi
 
     dev = entry->dev;
     msi_set_enable(dev, 0);
+    if ( entry->irq > 0 && !(irq_to_desc(entry->irq)->status & IRQ_GUEST) )
+        pci_intx(dev, 1);
 
     BUG_ON(list_empty(&dev->msi_list));
 }
--- a/xen/drivers/char/ns16550.c
+++ b/xen/drivers/char/ns16550.c
@@ -74,6 +74,7 @@ static struct ns16550 {
     u32 bar64;
     u16 cr;
     u8 bar_idx;
+    bool_t msi;
     const struct ns16550_config_param *param; /* Points into .init.*! */
 #endif
 } ns16550_com[2] = { { 0 } };
@@ -644,6 +645,16 @@ static void __init ns16550_init_preirq(s
         uart->fifo_size = 16;
 }
 
+static void __init ns16550_init_irq(struct serial_port *port)
+{
+#ifdef CONFIG_HAS_PCI
+    struct ns16550 *uart = port->uart;
+
+    if ( uart->msi )
+        uart->irq = create_irq(0);
+#endif
+}
+
 static void ns16550_setup_postirq(struct ns16550 *uart)
 {
     if ( uart->irq > 0 )
@@ -678,17 +689,6 @@ static void __init ns16550_init_postirq(
     uart->timeout_ms = max_t(
         unsigned int, 1, (bits * uart->fifo_size * 1000) / uart->baud);
 
-    if ( uart->irq > 0 )
-    {
-        uart->irqaction.handler = ns16550_interrupt;
-        uart->irqaction.name    = "ns16550";
-        uart->irqaction.dev_id  = port;
-        if ( (rc = setup_irq(uart->irq, 0, &uart->irqaction)) != 0 )
-            printk("ERROR: Failed to allocate ns16550 IRQ %d\n", uart->irq);
-    }
-
-    ns16550_setup_postirq(uart);
-
 #ifdef CONFIG_HAS_PCI
     if ( uart->bar || uart->ps_bdf_enable )
     {
@@ -709,8 +709,65 @@ static void __init ns16550_init_postirq(
                                     uart->ps_bdf[0], uart->ps_bdf[1],
                                     uart->ps_bdf[2]);
         }
+
+        if ( uart->msi )
+        {
+            struct msi_info msi = {
+                .bus = uart->ps_bdf[0],
+                .devfn = PCI_DEVFN(uart->ps_bdf[1], uart->ps_bdf[2]),
+                .irq = rc = uart->irq,
+                .entry_nr = 1
+            };
+
+            if ( rc > 0 )
+            {
+                struct msi_desc *msi_desc = NULL;
+
+                spin_lock(&pcidevs_lock);
+
+                rc = pci_enable_msi(&msi, &msi_desc);
+                if ( !rc )
+                {
+                    struct irq_desc *desc = irq_to_desc(msi.irq);
+                    unsigned long flags;
+
+                    spin_lock_irqsave(&desc->lock, flags);
+                    rc = setup_msi_irq(desc, msi_desc);
+                    spin_unlock_irqrestore(&desc->lock, flags);
+                    if ( rc )
+                        pci_disable_msi(msi_desc);
+                }
+
+                spin_unlock(&pcidevs_lock);
+
+                if ( rc )
+                {
+                    uart->irq = 0;
+                    if ( msi_desc )
+                        msi_free_irq(msi_desc);
+                    else
+                        destroy_irq(msi.irq);
+                }
+            }
+
+            if ( rc )
+                printk(XENLOG_WARNING
+                       "MSI setup failed (%d) for %02x:%02x.%o\n",
+                       rc, uart->ps_bdf[0], uart->ps_bdf[1], uart->ps_bdf[2]);
+        }
     }
 #endif
+
+    if ( uart->irq > 0 )
+    {
+        uart->irqaction.handler = ns16550_interrupt;
+        uart->irqaction.name    = "ns16550";
+        uart->irqaction.dev_id  = port;
+        if ( (rc = setup_irq(uart->irq, 0, &uart->irqaction)) != 0 )
+            printk("ERROR: Failed to allocate ns16550 IRQ %d\n", uart->irq);
+    }
+
+    ns16550_setup_postirq(uart);
 }
 
 static void ns16550_suspend(struct serial_port *port)
@@ -820,6 +877,7 @@ static const struct vuart_info *ns16550_
 
 static struct uart_driver __read_mostly ns16550_driver = {
     .init_preirq  = ns16550_init_preirq,
+    .init_irq     = ns16550_init_irq,
     .init_postirq = ns16550_init_postirq,
     .endboot      = ns16550_endboot,
     .suspend      = ns16550_suspend,
@@ -1123,7 +1181,18 @@ static void __init ns16550_parse_port_co
     }
 
     if ( *conf == ',' && *++conf != ',' )
-        uart->irq = simple_strtol(conf, &conf, 10);
+    {
+#ifdef CONFIG_HAS_PCI
+        if ( strncmp(conf, "msi", 3) == 0 )
+        {
+            conf += 3;
+            uart->msi = 1;
+            uart->irq = 0;
+        }
+        else
+#endif
+            uart->irq = simple_strtol(conf, &conf, 10);
+    }
 
 #ifdef CONFIG_HAS_PCI
     if ( *conf == ',' && *++conf != ',' )
--- a/xen/drivers/pci/pci.c
+++ b/xen/drivers/pci/pci.c
@@ -115,6 +115,21 @@ int pci_find_next_ext_capability(int seg
     return 0;
 }
 
+void pci_intx(const struct pci_dev *pdev, bool_t enable)
+{
+    uint16_t seg = pdev->seg;
+    uint8_t bus = pdev->bus;
+    uint8_t slot = PCI_SLOT(pdev->devfn);
+    uint8_t func = PCI_FUNC(pdev->devfn);
+    uint16_t cmd = pci_conf_read16(seg, bus, slot, func, PCI_COMMAND);
+
+    if ( enable )
+        cmd &= ~PCI_COMMAND_INTX_DISABLE;
+    else
+        cmd |= PCI_COMMAND_INTX_DISABLE;
+    pci_conf_write16(seg, bus, slot, func, PCI_COMMAND, cmd);
+}
+
 const char *__init parse_pci(const char *s, unsigned int *seg_p,
                              unsigned int *bus_p, unsigned int *dev_p,
                              unsigned int *func_p)
--- a/xen/include/xen/pci.h
+++ b/xen/include/xen/pci.h
@@ -152,6 +152,7 @@ int pci_find_next_ext_capability(int seg
 const char *parse_pci(const char *, unsigned int *seg, unsigned int *bus,
                       unsigned int *dev, unsigned int *func);
 
+void pci_intx(const struct pci_dev *, bool_t enable);
 bool_t pcie_aer_get_firmware_first(const struct pci_dev *);
 
 struct pirq;

Attachment: ns16550-MSI.patch
Description: Text document

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