Hi Lorenzo, On 07/02/19 9:45 PM, Lorenzo Pieralisi wrote: > On Thu, Feb 07, 2019 at 04:39:17PM +0530, Kishon Vijay Abraham I wrote: >> The legacy interrupt handler directly checks the IRQ_STATUS register >> corresponding to a interrupt line inorder to invoke generic_handle_irq. >> >> While this is okay for K2G platform which has separate interrupt line for >> each of the 4 legacy interrupts, AM654 which uses the same PCIe wrapper >> has a single interrupt line for all the legacy interrupts. So for AM654 >> the interrupt handler won't be able to directly check the IRQ_STATUS >> register corresponding to the interrupt line. >> >> Also the legacy interrupt handler uses 'virq' obtained from >> irq_of_parse_and_map to find the correct interrupt line which raised the >> interrupt. There is no guarantee that virq assigned for contiguous hardware >> irq will be contiguous and the interrupt handler might end up checking >> the wrong IRQ_STATUS register. >> >> In order to overcome the above issues, read the IRQ_STATUS register of >> all the 4 legacy interrupts to determine which interrupt was raised. >> >> Link: https://lkml.kernel.org/r/bb081d21-7c03-0357-4294-7e92d95d8...@arm.com >> Signed-off-by: Kishon Vijay Abraham I <kis...@ti.com> >> --- >> drivers/pci/controller/dwc/pci-keystone.c | 22 ++++++++++++---------- >> 1 file changed, 12 insertions(+), 10 deletions(-) >> >> diff --git a/drivers/pci/controller/dwc/pci-keystone.c >> b/drivers/pci/controller/dwc/pci-keystone.c >> index 5286a480f76b..4cf9849d5a1d 100644 >> --- a/drivers/pci/controller/dwc/pci-keystone.c >> +++ b/drivers/pci/controller/dwc/pci-keystone.c >> @@ -214,16 +214,11 @@ static void ks_pcie_handle_legacy_irq(struct >> keystone_pcie *ks_pcie, >> { >> struct dw_pcie *pci = ks_pcie->pci; >> struct device *dev = pci->dev; >> - u32 pending; >> int virq; >> >> - pending = ks_pcie_app_readl(ks_pcie, IRQ_STATUS(offset)); >> - >> - if (BIT(0) & pending) { >> - virq = irq_linear_revmap(ks_pcie->legacy_irq_domain, offset); >> - dev_dbg(dev, ": irq: irq_offset %d, virq %d\n", offset, virq); >> - generic_handle_irq(virq); >> - } >> + virq = irq_linear_revmap(ks_pcie->legacy_irq_domain, offset); >> + dev_dbg(dev, ": irq: irq_offset %d, virq %d\n", offset, virq); >> + generic_handle_irq(virq); >> >> /* EOI the INTx interrupt */ >> ks_pcie_app_writel(ks_pcie, IRQ_EOI, offset); >> @@ -607,8 +602,9 @@ static void ks_pcie_legacy_irq_handler(struct irq_desc >> *desc) >> struct keystone_pcie *ks_pcie = irq_desc_get_handler_data(desc); >> struct dw_pcie *pci = ks_pcie->pci; >> struct device *dev = pci->dev; >> - u32 irq_offset = irq - ks_pcie->legacy_host_irqs[0]; >> struct irq_chip *chip = irq_desc_get_chip(desc); >> + unsigned int irq_no; >> + u32 reg; >> >> dev_dbg(dev, ": Handling legacy irq %d\n", irq); >> >> @@ -618,7 +614,13 @@ static void ks_pcie_legacy_irq_handler(struct irq_desc >> *desc) >> * ack operation. >> */ >> chained_irq_enter(chip, desc); >> - ks_pcie_handle_legacy_irq(ks_pcie, irq_offset); >> + for (irq_no = 0; irq_no < PCI_NUM_INTX; irq_no++) { > > I understand the aim of this code but now on platforms where there > is a 1:1 relationship between Linux IRQ and INTX this loop has > steps carried out for nothing. > > If I understand the code correctly what this code does is force > looping over INTX status regs regardless of what linux IRQ number was > actually active.
right. This driver is used by 2 platforms K2G and AM654 (The patches are there on the list). K2G has 4 interrupt lines for each of the 4 legacy interrups while AM654 has a single interrupt line. One of the purpose of this patch is to have a single legacy interrupt handler for both K2G and AM654. > > You could do something faster by creating a matrix LinuxIRQ x INTx to > detect what INTx status register should actually be checked. > > This seems overkill to me but it is not that complicated to implement > and may clarify the code (and avoid reading up to three registers for > nothing on the IRQ code path, which can make things faster too). Agreed. But that's not possible for AM654 which has a single interrupt line and all the registers has to be read to identify the interrupt source. Thanks Kishon
