From: Daire McNamara daire.mcnamara@microchip.com
[ Upstream commit 7013654af694f6e1a2e699a6450ea50d309dd0e5 ]
Clear the MSI bit in ISTATUS_LOCAL register after reading it, but before reading and handling individual MSI bits from the ISTATUS_MSI register. This avoids a potential race where new MSI bits may be set on the ISTATUS_MSI register after it was read and be missed when the MSI bit in the ISTATUS_LOCAL register is cleared.
ISTATUS_LOCAL is a read/write/clear register; the register's bits are set when the corresponding interrupt source is activated. Each source is independent and thus multiple sources may be active simultaneously. The processor can monitor and clear status bits. If one or more ISTATUS_LOCAL interrupt sources are active, the RootPort issues an interrupt towards the processor (on the AXI domain). Bit 28 of this register reports an MSI has been received by the RootPort.
ISTATUS_MSI is a read/write/clear register. Bits 31-0 are asserted when an MSI with message number 31-0 is received by the RootPort. The processor must monitor and clear these bits.
Effectively, Bit 28 of ISTATUS_LOCAL informs the processor that an MSI has arrived at the RootPort and ISTATUS_MSI informs the processor which MSI (in the range 0 - 31) needs handling.
Reported by: Bjorn Helgaas bhelgaas@google.com Link: https://lore.kernel.org/linux-pci/20220127202000.GA126335@bhelgaas/
Link: https://lore.kernel.org/r/20220517141622.145581-1-daire.mcnamara@microchip.c... Fixes: 6f15a9c9f941 ("PCI: microchip: Add Microchip PolarFire PCIe controller driver") Signed-off-by: Daire McNamara daire.mcnamara@microchip.com Signed-off-by: Lorenzo Pieralisi lorenzo.pieralisi@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/pci/controller/pcie-microchip-host.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/drivers/pci/controller/pcie-microchip-host.c b/drivers/pci/controller/pcie-microchip-host.c index 329f930d17aa..fa209ad067bf 100644 --- a/drivers/pci/controller/pcie-microchip-host.c +++ b/drivers/pci/controller/pcie-microchip-host.c @@ -416,6 +416,7 @@ static void mc_handle_msi(struct irq_desc *desc)
status = readl_relaxed(bridge_base_addr + ISTATUS_LOCAL); if (status & PM_MSI_INT_MSI_MASK) { + writel_relaxed(status & PM_MSI_INT_MSI_MASK, bridge_base_addr + ISTATUS_LOCAL); status = readl_relaxed(bridge_base_addr + ISTATUS_MSI); for_each_set_bit(bit, &status, msi->num_vectors) { ret = generic_handle_domain_irq(msi->dev_domain, bit); @@ -432,13 +433,8 @@ static void mc_msi_bottom_irq_ack(struct irq_data *data) void __iomem *bridge_base_addr = port->axi_base_addr + MC_PCIE_BRIDGE_ADDR; u32 bitpos = data->hwirq; - unsigned long status;
writel_relaxed(BIT(bitpos), bridge_base_addr + ISTATUS_MSI); - status = readl_relaxed(bridge_base_addr + ISTATUS_MSI); - if (!status) - writel_relaxed(BIT(PM_MSI_INT_MSI_SHIFT), - bridge_base_addr + ISTATUS_LOCAL); }
static void mc_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)