[PATCH V9 1/2] PCI: handle CRS returned by device after FLR

On 8/10/2017 6:32 PM, Sinan Kaya wrote:

quoted

Alex was concerned that pci_bus_read_dev_vendor_id() could return
false ("no device here") with an ID value of ~0 for a functional VF
[1].

I think that is indeed possible:

  - a VF that is ready will return 0xffff as both Vendor ID and Device
    ID (SR-IOV r1.1, sec 3.4.1.1, .2), so the very first read in
    pci_bus_read_dev_vendor_id() would see 0xffffffff and return
    "false".

  - a VF that needs more time will return CRS and we'll loop in
    pci_bus_read_dev_vendor_id() until it becomes ready, and we'll
    return "true".

Falling into the code below for the "false" case probably will work,
but it's a little bit ugly because (a) we're using two mechanisms to
figure out when the device is ready for config requests, and (b) we
have to worry about VFs both in pci_bus_read_dev_vendor_id() and here
in the caller.

OK, I'm open to improving the code.

quoted

Here's an idea to make pci_bus_read_dev_vendor_id() work for both VFs
and PFs.  It can't distinguish the 0xffffffff from a VF vs one from a
non-existent device, but the caller might be able to pass that
information in, e.g., when we're enumerating and don't know whether
the device exists, we don't have a pci_dev and would use this:

How about creating a pci_bus_wait_crs() function with the loop in 
pci_bus_read_dev_vendor_id() and calling it from both places?

I prototyped both of the options. I found pci_bus_wait_crs() to be cleaner
due to this. 

is_vf looked like another hack like mine to tap into the CRS handling
inside the pci_bus_read_dev_vendor_id().

I think the right thing is to make CRS handling a first class citizen rather
than hiding it and overriding functions with unnecessary parameters.

I'll post V10 in a minute. It passed my testing.

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.