> -----Original Message----- > From: Logan Gunthorpe <log...@deltatee.com> > Sent: Wednesday, June 3, 2020 6:22 PM > > > On 2020-06-03 10:04 a.m., Stankiewicz, Piotr wrote: > >> -----Original Message----- > >> From: Logan Gunthorpe <log...@deltatee.com> > >> 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.stankiew...@intel.com> > >>> Reviewed-by: Andy Shevchenko <andriy.shevche...@intel.com> > >>> --- > >>> 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?
Having thought about it a bit more - the original behavior seems broken because in case someone asked for MSI only and that errored we'd always return -ENOSPC. So I went with your original suggestion of having a single return code (I just sent out a v3). Thanks, Piotr
