Re: Loading PCIe Device Driver at Dom0

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, May 23, 2012 at 04:43:55PM -0700, Kenneth Wong wrote:
> Dear all,
> 
> I have a PCIe device driver that I have been using on various Linux distributions and Kernel versions (2.6.x - 3.x.y) successfully all along.
> 
> I recently set up a Xen environment with Linux Mint 12 and Xen Hypervisor 4.1.  When I boot to Linux Mint, my driver still load (via insmod manually) successfully at Dom0 without any issue.  I can do reads and write to the hardware device.  But once booted to Xen, the driver failed to complete the driver load (via insmod manually) at Dom 0 and the console just hangs.
> 
> >From my debug messages, it appears it hangs because the driver doesn't receive any interrupt after a command is sent to the hardware device by writing a parameter to the mapped register.  Once that register is written, the device is expected to DMA the command from the buffer allocated by the driver.
> 
> The things that I can only think of that might have caused the problem are 1) IRQ mapping issue, or 2) DMA mapping issue, which I am not sure.

The 2).
> 
> 
> What the driver does:

You do need to use the PCI API (or the DMA API).

> 
> Set up a command buffer:
> Buf_t *buf = kmalloc(BUF_SIZE*sizeof(buf_t), GFP_KERNEL);
> unsigned long buf_addr = __pa(buf);
> unsigned int buf_addr_low = (unsigned int)buf_addr;
> 
> Tell device about the buffer:
> iowrite32(buf_addr_low, dev->pci_reg_map + BUF_ADR__LOW);

> 
> Set up IRQ:
>     if (pci_find_capability(dev, PCI_CAP_ID_MSI) &&
>         (!pci_enable_msi(dev)))
>     {
>         if (request_irq(dev->irq, func_msi_interrupt, IRQF_SHARED, DRIVER_NAME, my_dev))
>         {
>             return  -ENODEV;
>         }
>         my_dev->intr_mode = INTERRUPT_MSI;
>     }
> 
> Ask device to fetch command from buffer (Expect interrupt after this after device fetched the command from buf.  But interrupt did not happen.):
> iowrite32(buf_offset, dev->pci_reg_map + FETCH_CMD_REG);
> 
> 
> >From dmesg, it looks like IRQ initialization is complete.
> [  241.743769] My_driver initialization
> [  241.743787] xen: registering gsi 16 triggering 0 polarity 1
> [  241.743793] xen_map_pirq_gsi: returning irq 16 for gsi 16
> [  241.743795] xen: --> pirq=16 -> irq=16 (gsi=16)
> [  241.743801] Already setup the GSI :16
> [  241.743805] my-driver 0000:02:00.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
> [  241.743815] my-driver 0000:02:00.0: setting latency timer to 64
> 
> /proc/interrupts:
>             CPU0       CPU1       CPU2       CPU3       CPU4       CPU5       CPU6       CPU7
> ......
> ......
> 339:          0          0          0          0          0          0          0          0  xen-pirq-msi       my-driver
> ......
> ......
> 
> Any idea what might cause the problem?
> 
> Is there anything we have to be enable/disable, use different functions, or do differently in drivers written for Xen Dom0 environment regarding the following?
> 1)       Allocating a DMA buffer in driver to allow the device to DMA stuffs.
> 2)       Requesting MSI irq.
> 
> Please advise!
> 
> Thanks a lot in advance!!
> 
> Kenneth

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