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 <alexander.duyck at gmail.com> 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
