> On Apr 30, 2017, at 6:17 PM, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Sun, Apr 30, 2017 at 12:29:55PM -0700, Jim Harris wrote:
>> Some userspace drivers and frameworks only poll and do not
>> require interrupts to be available and enabled on the
>> PCI device. So remove the requirement that an IRQ is
>> assigned. If an IRQ is not assigned and a userspace
>> driver tries to read()/write(), the generic uio
>> framework will just return -EIO.
>>
>> This allows binding uio_pci_generic to devices which
>> cannot get an IRQ assigned, such as an NVMe controller
>> behind Intel Volume Management Device (VMD), since VMD
>> does not support INTx interrupts.
>>
>> Signed-off-by: Jim Harris <james.r.harris@xxxxxxxxx>
>
> Without interrupts, why do you want uio? All it does is
> forward interrupts to userspace.
Primarily so that a driver is bound to the device while using it from userspace. It can also be helpful to have the uioX sysfs symlinks to the underlying PCI config/resources.
Some userspace drivers/frameworks such as DPDK and SPDK primarily run in polled-only mode - not using interrupts at all. But DPDK does provide a facility to drop into interrupt mode which uio facilitates. So looking ahead to NVMe devices behind a VMD endpoint, we want to be able to at least bind uio to these NVMe devices - DPDK/SPDK just will not be able to drop into interrupt mode on these devices.
This is different obviously for vfio where we can allocate MSI/MSIX vectors. But for dev systems with IOMMU disabled, or passing a VMD endpoint to a guest VM, uio support is still desired.
>
>> ---
>> drivers/uio/uio_pci_generic.c | 20 +++++++++-----------
>> 1 file changed, 9 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
>> index d0b508b68f3c..81c59b4f8552 100644
>> --- a/drivers/uio/uio_pci_generic.c
>> +++ b/drivers/uio/uio_pci_generic.c
>> @@ -66,14 +66,7 @@ static int probe(struct pci_dev *pdev,
>> return err;
>> }
>>
>> - if (!pdev->irq) {
>> - dev_warn(&pdev->dev, "No IRQ assigned to device: "
>> - "no support for interrupts?\n");
>> - pci_disable_device(pdev);
>> - return -ENODEV;
>> - }
>> -
>> - if (!pci_intx_mask_supported(pdev)) {
>> + if (pci->irq && !pci_intx_mask_supported(pdev)) {
>> err = -ENODEV;
>> goto err_verify;
>> }
>> @@ -86,10 +79,15 @@ static int probe(struct pci_dev *pdev,
>>
>> 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;
>> + if (pdev->irq) {
>> + gdev->info.irq = pdev->irq;
>> + gdev->info.irq_flags = IRQF_SHARED;
>> + gdev->info.handler = irqhandler;
>> + } else {
>> + dev_warn(&pdev->dev, "No IRQ assigned to device: "
>> + "no support for interrupts?\n");
>> + }
>>
>> err = uio_register_device(&pdev->dev, &gdev->info);
>> if (err)
>> --
>> 2.12.2
