ppc/pnv: Fix loss of LPC SERIRQ interrupts

The LPC HC irq status register bits are set when an LPC IRQSER input is
asserted. These irq status bits drive the PSI irq to the CPU interrupt
controller. The LPC HC irq status bits are cleared by software writing
to the register with 1's for the bits to clear.

Existing register write was clearing the irq status bits even when the
input was asserted, this results in interrupts being lost.

This fix changes the behavior to keep track of the device IRQ status
in internal state that is separate from the irq status register, and
only allowing the irq status bits to be cleared if the associated
input is not asserted.

Signed-off-by: Glenn Miles <milesg@linux.ibm.com>
[np: rebased before P9 PSI SERIRQ patch, adjust changelog/comments]
Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

1 files changed, 19 insertions, 3 deletions

diff --git a/hw/ppc/pnv_lpc.c b/hw/ppc/pnv_lpc.c
index d692858bee..7d26b29487 100644
--- a/hw/ppc/pnv_lpc.c
+++ b/hw/ppc/pnv_lpc.c
@@ -505,7 +505,14 @@ static void lpc_hc_write(void *opaque, hwaddr addr, uint64_t val,
         pnv_lpc_eval_irqs(lpc);
         break;
     case LPC_HC_IRQSTAT:
-        lpc->lpc_hc_irqstat &= ~val;
+        /*
+         * This register is write-to-clear for the IRQSER (LPC device IRQ)
+         * status. However if the device has not de-asserted its interrupt
+         * that will just raise this IRQ status bit again. Model this by
+         * keeping track of the inputs and only clearing if the inputs are
+         * deasserted.
+         */
+        lpc->lpc_hc_irqstat &= ~(val & ~lpc->lpc_hc_irq_inputs);
         pnv_lpc_eval_irqs(lpc);
         break;
     case LPC_HC_ERROR_ADDRESS:
@@ -803,11 +810,20 @@ static void pnv_lpc_isa_irq_handler_cpld(void *opaque, int n, int level)
 static void pnv_lpc_isa_irq_handler(void *opaque, int n, int level)
 {
     PnvLpcController *lpc = PNV_LPC(opaque);
+    uint32_t irq_bit = LPC_HC_IRQ_SERIRQ0 >> n;
 
-    /* The Naples HW latches the 1 levels, clearing is done by SW */
     if (level) {
-        lpc->lpc_hc_irqstat |= LPC_HC_IRQ_SERIRQ0 >> n;
+        lpc->lpc_hc_irq_inputs |= irq_bit;
+
+        /*
+         * The LPC HC in Naples and later latches LPC IRQ into a bit field in
+         * the IRQSTAT register, and that drives the PSI IRQ to the IC.
+         * Software clears this bit manually (see LPC_HC_IRQSTAT handler).
+         */
+        lpc->lpc_hc_irqstat |= irq_bit;
         pnv_lpc_eval_irqs(lpc);
+    } else {
+        lpc->lpc_hc_irq_inputs &= ~irq_bit;
     }
 }