PCI: dwc: Move interrupt acking into the proper callback

The write to the status register is really an ACK for the HW,
and should be treated as such by the driver. Let's move it to the
irq_ack() callback, which will prevent people from moving it around
in order to paper over other bugs.

Fixes: 8c934095fa ("PCI: dwc: Clear MSI interrupt status after it is handled,
not before")
Fixes: 7c5925afbc ("PCI: dwc: Move MSI IRQs allocation to IRQ domains
hierarchical API")
Link: https://lore.kernel.org/linux-pci/20181113225734.8026-1-marc.zyngier@arm.com/
Reported-by: Trent Piepho <tpiepho@impinj.com>
Tested-by: Niklas Cassel <niklas.cassel@linaro.org>
Tested-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Tested-by: Stanimir Varbanov <svarbanov@mm-sol.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -99,9 +99,6 @@ irqreturn_t dw_handle_msi_irq(struct pcie_port *pp)
 					       (i * MAX_MSI_IRQS_PER_CTRL) +
 					       pos);
 			generic_handle_irq(irq);
-			dw_pcie_wr_own_conf(pp, PCIE_MSI_INTR0_STATUS +
-						(i * MSI_REG_CTRL_BLOCK_SIZE),
-					    4, 1 << pos);
 			pos++;
 		}
 	}
@@ -200,14 +197,18 @@ static void dw_pci_bottom_unmask(struct irq_data *data)
 
 static void dw_pci_bottom_ack(struct irq_data *d)
 {
-	struct msi_desc *msi = irq_data_get_msi_desc(d);
-	struct pcie_port *pp;
+	struct pcie_port *pp  = irq_data_get_irq_chip_data(d);
+	unsigned int res, bit, ctrl;
 	unsigned long flags;
 
-	pp = msi_desc_to_pci_sysdata(msi);
+	ctrl = d->hwirq / MAX_MSI_IRQS_PER_CTRL;
+	res = ctrl * MSI_REG_CTRL_BLOCK_SIZE;
+	bit = d->hwirq % MAX_MSI_IRQS_PER_CTRL;
 
 	raw_spin_lock_irqsave(&pp->lock, flags);
 
+	dw_pcie_wr_own_conf(pp, PCIE_MSI_INTR0_STATUS + res, 4, 1 << bit);
+
 	if (pp->ops->msi_irq_ack)
 		pp->ops->msi_irq_ack(d->hwirq, pp);