[src/trunk]: src/sys/dev/pci Better reading of 4.1.3.1, it seems that using 3...

[reinoud <reinoud%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/53652d8d8cb6
branches:  trunk
changeset: 951537:53652d8d8cb6
user:      reinoud <reinoud%NetBSD.org@localhost>
date:      Fri Feb 05 20:45:38 2021 +0000

description:
Better reading of 4.1.3.1, it seems that using 32 bit reads/writes is
mandatory for non-legacy devices.

diffstat:

 sys/dev/pci/virtio.c |  41 ++++++++++++++++++++++++++---------------
 1 files changed, 26 insertions(+), 15 deletions(-)

diffs (92 lines):

diff -r b770ba25c69d -r 53652d8d8cb6 sys/dev/pci/virtio.c
--- a/sys/dev/pci/virtio.c      Fri Feb 05 19:19:17 2021 +0000
+++ b/sys/dev/pci/virtio.c      Fri Feb 05 20:45:38 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: virtio.c,v 1.46 2021/02/05 19:18:23 reinoud Exp $      */
+/*     $NetBSD: virtio.c,v 1.47 2021/02/05 20:45:38 reinoud Exp $      */
 
 /*
  * Copyright (c) 2020 The NetBSD Foundation, Inc.
@@ -28,7 +28,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: virtio.c,v 1.46 2021/02/05 19:18:23 reinoud Exp $");
+__KERNEL_RCSID(0, "$NetBSD: virtio.c,v 1.47 2021/02/05 20:45:38 reinoud Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -204,7 +204,7 @@
 /*
  * The Virtio spec explicitly tells that reading and writing 8 bytes are not
  * considered atomic and no triggers may be connected to reading or writing
- * it. This allows for reading byte-by-byte.
+ * it. We access it using two 32 reads. See virtio spec 4.1.3.1.
  */
 uint64_t
 virtio_read_device_config_8(struct virtio_softc *sc, int index) {
@@ -212,12 +212,16 @@
        bus_space_handle_t ioh = sc->sc_devcfg_ioh;
        union {
                uint64_t u64;
-               uint8_t  b[8];
+               uint32_t l[2];
        } v;
        uint64_t val;
 
-       for (int i = 0; i < 8; i++)
-               v.b[i] = bus_space_read_1(iot, ioh, index + i);
+       v.l[0] = bus_space_read_4(iot, ioh, index);
+       v.l[1] = bus_space_read_4(iot, ioh, index + 4);
+       if (sc->sc_bus_endian != sc->sc_struct_endian) {
+               v.l[0] = bswap32(v.l[0]);
+               v.l[1] = bswap32(v.l[1]);
+       }
        val = v.u64;
 
        if (BYTE_ORDER != sc->sc_struct_endian)
@@ -306,8 +310,9 @@
 /*
  * The Virtio spec explicitly tells that reading and writing 8 bytes are not
  * considered atomic and no triggers may be connected to reading or writing
- * it. This allows for writing byte-by-byte. For good measure it is stated to
- * always write lsb first just in case of a hypervisor bug.
+ * it. We access it using two 32 bit writes. For good measure it is stated to
+ * always write lsb first just in case of a hypervisor bug. See See virtio
+ * spec 4.1.3.1.
  */
 void
 virtio_write_device_config_8(struct virtio_softc *sc, int index, uint64_t value)
@@ -316,19 +321,25 @@
        bus_space_handle_t ioh = sc->sc_devcfg_ioh;
        union {
                uint64_t u64;
-               uint8_t  b[8];
+               uint32_t l[2];
        } v;
 
        if (BYTE_ORDER != sc->sc_struct_endian)
                value = bswap64(value);
 
        v.u64 = value;
-       if (sc->sc_struct_endian == LITTLE_ENDIAN)
-               for (int i = 0; i < 8; i++)
-                       bus_space_write_1(iot, ioh, index + i, v.b[i]);
-       else
-               for (int i = 7; i >= 0; i--)
-                       bus_space_write_1(iot, ioh, index + i, v.b[i]);
+       if (sc->sc_bus_endian != sc->sc_struct_endian) {
+               v.l[0] = bswap32(v.l[0]);
+               v.l[1] = bswap32(v.l[1]);
+       }
+
+       if (sc->sc_struct_endian == LITTLE_ENDIAN) {
+               bus_space_write_4(iot, ioh, index,     v.l[0]);
+               bus_space_write_4(iot, ioh, index + 4, v.l[1]);
+       } else {
+               bus_space_write_4(iot, ioh, index + 4, v.l[1]);
+               bus_space_write_4(iot, ioh, index,     v.l[0]);
+       }
 }
 
 /*