FYI: I've just posted to linux-kernel list patches that add support for
both MSI and MSI-X interrupt modes to uio_pci_generic driver.
It addresses most (all) remarks on this thread and also fixes some
issues this code has, e.g. not disabling msi-x in remove(), etc.
U are all welcome to comment... ;)
thanks,
vlad
On 10/02/15 04:39, Alexander Duyck wrote:
On 10/01/2015 05:04 PM, Stephen Hemminger wrote:
On Thu, 1 Oct 2015 16:43:23 -0700
Alexander Duyck <[email protected]> wrote:
Yes, but in the case of something like a VF it is going to just make a
bigger mess of things since INTx doesn't work. So what would you
expect
your driver to do in that case? Also we have to keep in mind that the
MSI-X failure case is very unlikely.
One other thing that just occurred to me is that you may want to try
using the range allocation call instead of a hard set number of
interrupts. Then if you start running short on vectors you don't hard
fail and instead just allocate what you can.
I tried that but the bookkeeping gets messy since there is no good
way to communicate that back to userspace and have it adapt.
Actually I kind of just realized that uio_msi_open is kind of messed
up. So if the MSI-X allocation fails due to no resources it will
return a positive value indicating the number of vectors that could be
allocated, a negative value if one of the input values is invalid, or
0. I'm not sure if returning a positive value on failure is an issue
or not. I know the open call is supposed to return a negative value
or the file descriptor if not negative. I don't know if the return
value might be interpreted as a file descriptor or not.
Also if MSI-X is supported by the hardware, but disabled for some
reason by the kernel ("pci=nomsi") then this driver is rendered
inoperable since it will never give you anything but -EINVAL from the
open call.
I really think you should probably look at taking care of enabling
MSI-X and maybe MSI as a fall-back in probe. At least then you can
post a message about how many vectors are enabled and what type. Then
if you cannot enable any interrupts due to MSI being disabled you can
simply fail at probe time and let then load a different driver.
- Alex
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