uio: add generic driver for PCI 2.3 devices

This adds a generic uio driver that can bind to any PCI device.  First
user will be virtualization where a qemu userspace process needs to give
guest OS access to the device.

Interrupts are handled using the Interrupt Disable bit in the PCI
command register and Interrupt Status bit in the PCI status register.
All devices compliant to PCI 2.3 (circa 2002) and all compliant PCI
Express devices should support these bits.  Driver detects this support,
and won't bind to devices which do not support the Interrupt Disable Bit
in the command register.

It's expected that more features of interest to virtualization will be
added to this driver in the future. Possibilities are: mmap for device
resources, MSI/MSI-X, eventfd (to interface with kvm), iommu.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Hans J. Koch <hjk@linutronix.de>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

3 files changed, 218 insertions, 0 deletions

diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
index 45200fd68534..8aa1955f35ed 100644
--- a/drivers/uio/Kconfig
+++ b/drivers/uio/Kconfig
@@ -84,4 +84,14 @@ config UIO_SERCOS3
 
           If you compile this as a module, it will be called uio_sercos3.
 
+config UIO_PCI_GENERIC
+        tristate "Generic driver for PCI 2.3 and PCI Express cards"
+        depends on PCI
+        default n
+        help
+          Generic driver that you can bind, dynamically, to any
+          PCI 2.3 compliant and PCI Express card. It is useful,
+          primarily, for virtualization scenarios.
+          If you compile this as a module, it will be called uio_pci_generic.
+
 endif
diff --git a/drivers/uio/Makefile b/drivers/uio/Makefile
index 5c2586d75797..73b2e7516729 100644
--- a/drivers/uio/Makefile
+++ b/drivers/uio/Makefile
@@ -5,3 +5,4 @@ obj-$(CONFIG_UIO_PDRV_GENIRQ)	+= uio_pdrv_genirq.o
 obj-$(CONFIG_UIO_SMX)   += uio_smx.o
 obj-$(CONFIG_UIO_AEC)   += uio_aec.o
 obj-$(CONFIG_UIO_SERCOS3)       += uio_sercos3.o
+obj-$(CONFIG_UIO_PCI_GENERIC)   += uio_pci_generic.o
diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
new file mode 100644
index 000000000000..313da35984af
--- /dev/null
+++ b/drivers/uio/uio_pci_generic.c
@@ -0,0 +1,207 @@
+/* uio_pci_generic - generic UIO driver for PCI 2.3 devices
+ *
+ * Copyright (C) 2009 Red Hat, Inc.
+ * Author: Michael S. Tsirkin <mst@redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * Since the driver does not declare any device ids, you must allocate
+ * id and bind the device to the driver yourself.  For example:
+ *
+ * # echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id
+ * # echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind
+ * # echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind
+ * # ls -l /sys/bus/pci/devices/0000:00:19.0/driver
+ * .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic
+ *
+ * Driver won't bind to devices which do not support the Interrupt Disable Bit
+ * in the command register. All devices compliant to PCI 2.3 (circa 2002) and
+ * all compliant PCI Express devices should support this bit.
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/pci.h>
+#include <linux/uio_driver.h>
+#include <linux/spinlock.h>
+
+#define DRIVER_VERSION  "0.01.0"
+#define DRIVER_AUTHOR   "Michael S. Tsirkin <mst@redhat.com>"
+#define DRIVER_DESC     "Generic UIO driver for PCI 2.3 devices"
+
+struct uio_pci_generic_dev {
+        struct uio_info info;
+        struct pci_dev *pdev;
+        spinlock_t lock; /* guards command register accesses */
+};
+
+static inline struct uio_pci_generic_dev *
+to_uio_pci_generic_dev(struct uio_info *info)
+{
+        return container_of(info, struct uio_pci_generic_dev, info);
+}
+
+/* Interrupt handler. Read/modify/write the command register to disable
+ * the interrupt. */
+static irqreturn_t irqhandler(int irq, struct uio_info *info)
+{
+        struct uio_pci_generic_dev *gdev = to_uio_pci_generic_dev(info);
+        struct pci_dev *pdev = gdev->pdev;
+        irqreturn_t ret = IRQ_NONE;
+        u32 cmd_status_dword;
+        u16 origcmd, newcmd, status;
+
+        /* We do a single dword read to retrieve both command and status.
+         * Document assumptions that make this possible. */
+        BUILD_BUG_ON(PCI_COMMAND % 4);
+        BUILD_BUG_ON(PCI_COMMAND + 2 != PCI_STATUS);
+
+        spin_lock_irq(&gdev->lock);
+        pci_block_user_cfg_access(pdev);
+
+        /* Read both command and status registers in a single 32-bit operation.
+         * Note: we could cache the value for command and move the status read
+         * out of the lock if there was a way to get notified of user changes
+         * to command register through sysfs. Should be good for shared irqs. */
+        pci_read_config_dword(pdev, PCI_COMMAND, &cmd_status_dword);
+        origcmd = cmd_status_dword;
+        status = cmd_status_dword >> 16;
+
+        /* Check interrupt status register to see whether our device
+         * triggered the interrupt. */
+        if (!(status & PCI_STATUS_INTERRUPT))
+                goto done;
+
+        /* We triggered the interrupt, disable it. */
+        newcmd = origcmd | PCI_COMMAND_INTX_DISABLE;
+        if (newcmd != origcmd)
+                pci_write_config_word(pdev, PCI_COMMAND, newcmd);
+
+        /* UIO core will signal the user process. */
+        ret = IRQ_HANDLED;
+done:
+
+        pci_unblock_user_cfg_access(pdev);
+        spin_unlock_irq(&gdev->lock);
+        return ret;
+}
+
+/* Verify that the device supports Interrupt Disable bit in command register,
+ * per PCI 2.3, by flipping this bit and reading it back: this bit was readonly
+ * in PCI 2.2. */
+static int __devinit verify_pci_2_3(struct pci_dev *pdev)
+{
+        u16 orig, new;
+        int err = 0;
+
+        pci_block_user_cfg_access(pdev);
+        pci_read_config_word(pdev, PCI_COMMAND, &orig);
+        pci_write_config_word(pdev, PCI_COMMAND,
+                              orig ^ PCI_COMMAND_INTX_DISABLE);
+        pci_read_config_word(pdev, PCI_COMMAND, &new);
+        /* There's no way to protect against
+         * hardware bugs or detect them reliably, but as long as we know
+         * what the value should be, let's go ahead and check it. */
+        if ((new ^ orig) & ~PCI_COMMAND_INTX_DISABLE) {
+                err = -EBUSY;
+                dev_err(&pdev->dev, "Command changed from 0x%x to 0x%x: "
+                        "driver or HW bug?\n", orig, new);
+                goto err;
+        }
+        if (!((new ^ orig) & PCI_COMMAND_INTX_DISABLE)) {
+                dev_warn(&pdev->dev, "Device does not support "
+                         "disabling interrupts: unable to bind.\n");
+                err = -ENODEV;
+                goto err;
+        }
+        /* Now restore the original value. */
+        pci_write_config_word(pdev, PCI_COMMAND, orig);
+err:
+        pci_unblock_user_cfg_access(pdev);
+        return err;
+}
+
+static int __devinit probe(struct pci_dev *pdev,
+                           const struct pci_device_id *id)
+{
+        struct uio_pci_generic_dev *gdev;
+        int err;
+
+        if (!pdev->irq) {
+                dev_warn(&pdev->dev, "No IRQ assigned to device: "
+                         "no support for interrupts?\n");
+                return -ENODEV;
+        }
+
+        err = pci_enable_device(pdev);
+        if (err) {
+                dev_err(&pdev->dev, "%s: pci_enable_device failed: %d\n",
+                        __func__, err);
+                return err;
+        }
+
+        err = verify_pci_2_3(pdev);
+        if (err)
+                goto err_verify;
+
+        gdev = kzalloc(sizeof(struct uio_pci_generic_dev), GFP_KERNEL);
+        if (!gdev) {
+                err = -ENOMEM;
+                goto err_alloc;
+        }
+
+        gdev->info.name = "uio_pci_generic";
+        gdev->info.version = DRIVER_VERSION;
+        gdev->info.irq = pdev->irq;
+        gdev->info.irq_flags = IRQF_SHARED;
+        gdev->info.handler = irqhandler;
+        gdev->pdev = pdev;
+        spin_lock_init(&gdev->lock);
+
+        if (uio_register_device(&pdev->dev, &gdev->info))
+                goto err_register;
+        pci_set_drvdata(pdev, gdev);
+
+        return 0;
+err_register:
+        kfree(gdev);
+err_alloc:
+err_verify:
+        pci_disable_device(pdev);
+        return err;
+}
+
+static void remove(struct pci_dev *pdev)
+{
+        struct uio_pci_generic_dev *gdev = pci_get_drvdata(pdev);
+
+        uio_unregister_device(&gdev->info);
+        pci_disable_device(pdev);
+        kfree(gdev);
+}
+
+static struct pci_driver driver = {
+        .name = "uio_pci_generic",
+        .id_table = NULL, /* only dynamic id's */
+        .probe = probe,
+        .remove = remove,
+};
+
+static int __init init(void)
+{
+        pr_info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
+        return pci_register_driver(&driver);
+}
+
+static void __exit cleanup(void)
+{
+        pci_unregister_driver(&driver);
+}
+
+module_init(init);
+module_exit(cleanup);
+
+MODULE_VERSION(DRIVER_VERSION);
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);