On 2020-06-03 10:04 a.m., Stankiewicz, Piotr wrote: >> -----Original Message----- >> From: Logan Gunthorpe <logang@xxxxxxxxxxxx> >> Sent: Wednesday, June 3, 2020 5:48 PM >> >> >> >> On 2020-06-03 5:44 a.m., Piotr Stankiewicz wrote: >>> When debugging an issue where I was asking the PCI machinery to enable a >>> set of MSI-X vectors, without falling back on MSI, I ran across a >>> behaviour which seems odd. The pci_alloc_irq_vectors_affinity() will >>> always return -ENOSPC on failure, when allocating MSI-X vectors only, >>> whereas with MSI fallback it will forward any error returned by >>> __pci_enable_msi_range(). This is a confusing behaviour, so have the >>> pci_alloc_irq_vectors_affinity() forward the error code from >>> __pci_enable_msix_range() when appropriate. >>> >>> Signed-off-by: Piotr Stankiewicz <piotr.stankiewicz@xxxxxxxxx> >>> Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> >>> --- >>> drivers/pci/msi.c | 5 +++-- >>> 1 file changed, 3 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c >>> index 6b43a5455c7a..443cc324b196 100644 >>> --- a/drivers/pci/msi.c >>> +++ b/drivers/pci/msi.c >>> @@ -1231,8 +1231,9 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev >> *dev, unsigned int min_vecs, >>> } >>> } >>> >>> - if (msix_vecs == -ENOSPC) >>> - return -ENOSPC; >>> + if (msix_vecs == -ENOSPC || >>> + (flags & (PCI_IRQ_MSI | PCI_IRQ_MSIX)) == PCI_IRQ_MSIX) >>> + return msix_vecs; >>> return msi_vecs; >>> } >>> EXPORT_SYMBOL(pci_alloc_irq_vectors_affinity); >>> >> >> It occurs to me that we could clean this function up a bit more... I >> don't see any need to have two variables for msi_vecs and msix_vecs and >> then have a complicated bit of logic at the end to decide which to return. >> >> Why not instead just have one variable which is set by >> __pci_enable_msix_range(), then __pci_enable_msi_range(), then returned >> if they both fail? >> > > That wouldn't preserve the original bit of logic where -ENOSPC is returned > any time __pci_enable_msix_range() fails with -ENOSPC, irrespective of whether > MSI fallback was requested. Though I don't know if that is desired behaviour. That does look very odd, but ok... Then, couldn't we just set msi_vecs to msix_vecs after calling __pci_enable_msix_range() such that if __pci_enable_msi_range() doesn't get called we will return the same error without needing the messy second conditional? Logan
