iwm: interrupt cleanup

[Tobias Heider]

Hi,

here are some small improvements for iwm's interrupt handler.

- Hardware errors (r1 == 0xffffffff || (r1 & 0xfffffff0) == 0xa5a5a5a0) should
  be checked in both cases (ict and non-ict).
- r1 and r2 should be uint32, they are read with bus_space_read_4()
- (Slightly) better explanation for hardware bug mitigation

ok?

diff --git a/sys/dev/pci/if_iwm.c b/sys/dev/pci/if_iwm.c
index 34877135003..518595c601e 100644
--- a/sys/dev/pci/if_iwm.c
+++ b/sys/dev/pci/if_iwm.c
@@ -8589,8 +8589,9 @@ iwm_intr(void *arg)
 {
        struct iwm_softc *sc = arg;
        int handled = 0;
-       int r1, r2, rv = 0;
+       int rv = 0;
        int isperiodic = 0;
+       uint32_t r1, r2;
 
        IWM_WRITE(sc, IWM_CSR_INT_MASK, 0);
 
@@ -8617,19 +8618,24 @@ iwm_intr(void *arg)
                if (r1 == 0xffffffff)
                        r1 = 0;
 
-               /* i am not expected to understand this */
+               /*
+                * Workaround for hardware bug where bits are falsely cleared
+                * when using interrupt coalescing.  Bit 15 should be set if
+                * bits 18 and 19 are set.
+                */
                if (r1 & 0xc0000)
                        r1 |= 0x8000;
+
                r1 = (0xff & r1) | ((0xff00 & r1) << 16);
        } else {
                r1 = IWM_READ(sc, IWM_CSR_INT);
-               if (r1 == 0xffffffff || (r1 & 0xfffffff0) == 0xa5a5a5a0)
-                       goto out;
                r2 = IWM_READ(sc, IWM_CSR_FH_INT_STATUS);
        }
        if (r1 == 0 && r2 == 0) {
                goto out_ena;
        }
+       if (r1 == 0xffffffff || (r1 & 0xfffffff0) == 0xa5a5a5a0)
+               goto out;
 
        IWM_WRITE(sc, IWM_CSR_INT, r1 | ~sc->sc_intmask);