On Tue, Aug 02, 2016 at 09:11:09PM +0000, Chitturi, Divakar wrote:
> Hi
>
> Below are two scenarios for which i would like to understand the right
> way to assign the BAR address for my PCI device
>
> Device details:
> pci switch upstrem port connected to root complex
> pci switch downstream port 1 connected to my_pci_device
> my_pci_device is FPGA
> FPGA has bunch of controllers and other logic
>
> Driver details:
> Have a dedicated pci kernel driver for my_device
> Enabled pcihp kernel driver
Which pci hotplug driver? Just the PCI Hotplug core isn't going to do
anything, you need a controller driver for your specific PCI hotplug
hardware.
> At power on, BIOS assigns/reserves specific region of memory for my pci device.
> during the linux boot process, pci core will assign the bar and other initialization and call my
> probe function in the driver. probe function will perform some initialization which includes reading
> the BAR and setting some registers in IO space of the device.
>
> Scn1:
> At some point the device is removed and reinserted
>
> Scn2:
> At some point similar device is inserted in a new pci slot
How are they added/removed without a hotplug controller?
> In both the scenarios explained about, BIOS is not involved as system was never turned off completely. So
> 1. how do we obtain the BAR address for the device.
What architecture is this? x86? If so, it just uses whatever the BIOS
said was there for the last time.
> 2. Should i assign it explicitly?
Yes.
> 3. if yes, should it be done in my driver ( in both the case i am assuming driver's probe function will be called )
No, in your pci hotplug driver, you need to handle it there.
> 4. can i use pci_assign_resource() in drivers probe function
Nope.
> 5. is something like below the right way to do it ?
>
> static int my_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> {
> if( pci_resource_start (pdev,BAR0) <= 0) {
> pr_debug(" Assign BAR0 \n");
> ret = pci_assign_resource(pdev,BAR0);
> if( 0 > ret) {
> dev_err(&pdev->dev, " Failed to assign resource \n");
> return ret;
> }
> }
>
> ret = pci_enable_device(pdev);
> ret = pci_request_regions(pdev, dev_driver_string(&pdev->dev));
> base_addr = pci_iomap(pdev, BAR0, 0);
> }
You need to write a pci hotplug controller driver to manage the
resources and assign them properly. That's its responsibility, see the
PCI hotplug specification for all of the details...
good luck!
greg k-h
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