ppc/pnv: raise no-response errors if an LPC transaction fails

If nothing responds to an LPC access, the LPC host controller should
set an IRQSTAT error. Model this behaviour.

skiboot uses this error to "probe" LPC accesses, among other things to
determine if a SuperIO chip is present. After this change it recognizes
there is no SuperIO present and does not keep trying to access it.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

hw/ppc/pnv_lpc.c

@@ -353,6 +353,8 @@ static const MemoryRegionOps pnv_lpc_xscom_ops = {
     .endianness = DEVICE_BIG_ENDIAN,
 };
 
+static void pnv_lpc_opb_noresponse(PnvLpcController *lpc);
+
 static uint64_t pnv_lpc_mmio_read(void *opaque, hwaddr addr, unsigned size)
 {
     PnvLpcController *lpc = PNV_LPC(opaque);
@@ -376,6 +378,7 @@ static uint64_t pnv_lpc_mmio_read(void *opaque, hwaddr addr, unsigned size)
     }
 
     if (result != MEMTX_OK) {
+        pnv_lpc_opb_noresponse(lpc);
         qemu_log_mask(LOG_GUEST_ERROR, "OPB read failed at @0x%"
                       HWADDR_PRIx "\n", addr);
     }
@@ -406,6 +409,7 @@ static void pnv_lpc_mmio_write(void *opaque, hwaddr addr,
     }
 
     if (result != MEMTX_OK) {
+        pnv_lpc_opb_noresponse(lpc);
         qemu_log_mask(LOG_GUEST_ERROR, "OPB write failed at @0x%"
                       HWADDR_PRIx "\n", addr);
     }
@@ -511,6 +515,12 @@ static void pnv_lpc_eval_irqs(PnvLpcController *lpc)
     qemu_set_irq(lpc->psi_irq_lpchc, lpc->opb_irq_stat != 0);
 }
 
+static void pnv_lpc_opb_noresponse(PnvLpcController *lpc)
+{
+    lpc->lpc_hc_irqstat |= LPC_HC_IRQ_SYNC_NORESP_ERR;
+    pnv_lpc_eval_irqs(lpc);
+}
+
 static uint64_t lpc_hc_read(void *opaque, hwaddr addr, unsigned size)
 {
     PnvLpcController *lpc = opaque;