Hi Kulkarni, On 3/13/23 2:12 PM, Bjorn Helgaas wrote: > On Mon, Feb 27, 2023 at 08:21:36PM -0800, Ganapatrao Kulkarni wrote: >> As per PCI specification (PCI Express Base Specification Revision >> 6.0, Section 10.5) both PF and VFs of a PCI EP are permitted to be enabled >> independently for ATS capability, however the STU(Smallest Translation >> Unit) is shared between PF and VFs. For VFs, it is hardwired to Zero and >> the associated PF's value applies to VFs. >> >> In the current code, the STU is being configured while enabling the PF ATS. >> Hence, it is not able to enable ATS for VFs, if it is not enabled on the >> associated PF already. >> >> Adding a function pci_ats_stu_configure(), which can be called to >> configure the STU during PF enumeration. >> Latter enumerations of VFs can successfully enable ATS independently. > > s/STU(Smallest/STU (Smallest/ (add space before paren) > s/Adding a function pci_ats_stu_configure()/Add pci_ats_stu_configure()/ > s/Latter/Subsequent/ > > Add blank line between paragraphs (it looks like "Latter enumerations" > is intended to start a new paragraph). > >> Signed-off-by: Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx> > > Acked-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > > Given an ack for the IOMMU patch, I'd be happy to merge both (and I > can do the commit log tweaks); just let me know. > > One comment/question below. > >> --- >> drivers/pci/ats.c | 33 +++++++++++++++++++++++++++++++-- >> include/linux/pci-ats.h | 3 +++ >> 2 files changed, 34 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c >> index f9cc2e10b676..1611bfa1d5da 100644 >> --- a/drivers/pci/ats.c >> +++ b/drivers/pci/ats.c >> @@ -46,6 +46,35 @@ bool pci_ats_supported(struct pci_dev *dev) >> } >> EXPORT_SYMBOL_GPL(pci_ats_supported); >> >> +/** >> + * pci_ats_stu_configure - Configure STU of a PF. >> + * @dev: the PCI device >> + * @ps: the IOMMU page shift >> + * >> + * Returns 0 on success, or negative on failure. >> + */ >> +int pci_ats_stu_configure(struct pci_dev *dev, int ps) >> +{ >> + u16 ctrl; >> + >> + if (dev->ats_enabled || dev->is_virtfn) >> + return 0; > > I might return an error for the VF case on the assumption that it's > likely an error in the caller. I guess one could argue that it > simplifies the caller if it doesn't have to check for PF vs VF. But > the fact that STU is shared between PF and VFs is an important part of > understanding how ATS works, so the caller should be aware of the > distinction anyway. I have already asked this question. But let me repeat it. We don't have any checks for the PF case here. That means you can re-configure the STU as many times as you want until ATS is enabled in PF. So, if there are active VFs which uses this STU, can PF re-configure the STU at will? > >> + >> + if (!pci_ats_supported(dev)) >> + return -EINVAL; >> + >> + if (ps < PCI_ATS_MIN_STU) >> + return -EINVAL; >> + >> + dev->ats_stu = ps; >> + pci_read_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, &ctrl); >> + ctrl |= PCI_ATS_CTRL_STU(dev->ats_stu - PCI_ATS_MIN_STU); >> + pci_write_config_word(dev, dev->ats_cap + PCI_ATS_CTRL, ctrl); >> + >> + return 0; >> +} >> +EXPORT_SYMBOL_GPL(pci_ats_stu_configure); >> + >> /** >> * pci_enable_ats - enable the ATS capability >> * @dev: the PCI device >> @@ -68,8 +97,8 @@ int pci_enable_ats(struct pci_dev *dev, int ps) >> return -EINVAL; >> >> /* >> - * Note that enabling ATS on a VF fails unless it's already enabled >> - * with the same STU on the PF. >> + * Note that enabling ATS on a VF fails unless it's already >> + * configured with the same STU on the PF. >> */ >> ctrl = PCI_ATS_CTRL_ENABLE; >> if (dev->is_virtfn) { >> diff --git a/include/linux/pci-ats.h b/include/linux/pci-ats.h >> index df54cd5b15db..7d62a92aaf23 100644 >> --- a/include/linux/pci-ats.h >> +++ b/include/linux/pci-ats.h >> @@ -8,6 +8,7 @@ >> /* Address Translation Service */ >> bool pci_ats_supported(struct pci_dev *dev); >> int pci_enable_ats(struct pci_dev *dev, int ps); >> +int pci_ats_stu_configure(struct pci_dev *dev, int ps); >> void pci_disable_ats(struct pci_dev *dev); >> int pci_ats_queue_depth(struct pci_dev *dev); >> int pci_ats_page_aligned(struct pci_dev *dev); >> @@ -16,6 +17,8 @@ static inline bool pci_ats_supported(struct pci_dev *d) >> { return false; } >> static inline int pci_enable_ats(struct pci_dev *d, int ps) >> { return -ENODEV; } >> +static inline int pci_ats_stu_configure(struct pci_dev *d, int ps) >> +{ return -ENODEV; } >> static inline void pci_disable_ats(struct pci_dev *d) { } >> static inline int pci_ats_queue_depth(struct pci_dev *d) >> { return -ENODEV; } >> -- >> 2.38.1 >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- Sathyanarayanan Kuppuswamy Linux Kernel Developer