[src/trunk]: src/sys/dev virtio(4): Fix byte order of DMA data for armeb in t...

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

details:   https://anonhg.NetBSD.org/src/rev/e3ed7e3e2649
branches:  trunk
changeset: 377315:e3ed7e3e2649
user:      rin <rin%NetBSD.org@localhost>
date:      Fri Jul 07 07:19:36 2023 +0000

description:
virtio(4): Fix byte order of DMA data for armeb in the same manner as
aarch64eb.

Fix comments to explain what is going on for {arm,aarch64}eb on QEMU.
This is not due to QEMU bugs; it correctly configures everything for
little-endian environment, and we forcibly change byte order only for
CPU cores during kernel bootstrap.

diffstat:

 sys/dev/pci/virtio_pci.c     |  19 ++++++++++---------
 sys/dev/virtio/virtio_mmio.c |  10 ++++------
 2 files changed, 14 insertions(+), 15 deletions(-)

diffs (75 lines):

diff -r 0e3649f8d3bf -r e3ed7e3e2649 sys/dev/pci/virtio_pci.c
--- a/sys/dev/pci/virtio_pci.c  Fri Jul 07 07:04:17 2023 +0000
+++ b/sys/dev/pci/virtio_pci.c  Fri Jul 07 07:19:36 2023 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: virtio_pci.c,v 1.42 2023/04/19 00:23:45 yamaguchi Exp $ */
+/* $NetBSD: virtio_pci.c,v 1.43 2023/07/07 07:19:36 rin Exp $ */
 
 /*
  * Copyright (c) 2020 The NetBSD Foundation, Inc.
@@ -28,7 +28,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: virtio_pci.c,v 1.42 2023/04/19 00:23:45 yamaguchi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: virtio_pci.c,v 1.43 2023/07/07 07:19:36 rin Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -138,15 +138,16 @@ static bool       virtio_pci_msix_enabled(stru
 #define VIRTIO_MSIX_QUEUE_VECTOR_INDEX 1
 
 /*
- * When using PCI attached virtio on aarch64-eb under Qemu, the IO space
- * suddenly read BIG_ENDIAN where it should stay LITTLE_ENDIAN. The data read
- * 1 byte at a time seem OK but reading bigger lengths result in swapped
- * endian. This is most notable on reading 8 byters since we can't use
- * bus_space_{read,write}_8().
+ * For big-endian aarch64/armv7 on QEMU (and most real HW), only CPU cores
+ * are running in big-endian mode, with all peripheral being configured to
+ * little-endian mode. Their default bus_space(9) functions forcibly swap
+ * byte-order. This guarantees that PIO'ed data from pci(4), e.g., are
+ * correctly handled by bus_space(9), while DMA'ed ones should be swapped
+ * by hand, in violation of virtio(4) specifications.
  */
 
-#if defined(__aarch64__) && BYTE_ORDER == BIG_ENDIAN
-#      define READ_ENDIAN_09   BIG_ENDIAN      /* should be LITTLE_ENDIAN */
+#if (defined(__aarch64__) || defined(__arm__)) && BYTE_ORDER == BIG_ENDIAN
+#      define READ_ENDIAN_09   BIG_ENDIAN
 #      define READ_ENDIAN_10   BIG_ENDIAN
 #      define STRUCT_ENDIAN_09 BIG_ENDIAN
 #      define STRUCT_ENDIAN_10 LITTLE_ENDIAN
diff -r 0e3649f8d3bf -r e3ed7e3e2649 sys/dev/virtio/virtio_mmio.c
--- a/sys/dev/virtio/virtio_mmio.c      Fri Jul 07 07:04:17 2023 +0000
+++ b/sys/dev/virtio/virtio_mmio.c      Fri Jul 07 07:19:36 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: virtio_mmio.c,v 1.10 2023/04/19 00:23:45 yamaguchi Exp $       */
+/*     $NetBSD: virtio_mmio.c,v 1.11 2023/07/07 07:19:36 rin Exp $     */
 /*     $OpenBSD: virtio_mmio.c,v 1.2 2017/02/24 17:12:31 patrick Exp $ */
 
 /*
@@ -29,7 +29,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: virtio_mmio.c,v 1.10 2023/04/19 00:23:45 yamaguchi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: virtio_mmio.c,v 1.11 2023/07/07 07:19:36 rin Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -68,12 +68,10 @@
 /*
  * MMIO configuration space for virtio-mmio v1 is in guest byte order.
  *
- * XXX Note that aarch64eb pretends to be little endian. the MMIO registers
- * are in little endian but the device config registers and data structures
- * are in big endian; this is due to a bug in current Qemu.
+ * XXX For big-endian aarch64 and arm, see note in virtio_pci.c.
  */
 
-#if defined(__aarch64__) && BYTE_ORDER == BIG_ENDIAN
+#if (defined(__aarch64__) || defined(__arm__)) && BYTE_ORDER == BIG_ENDIAN
 #      define READ_ENDIAN      LITTLE_ENDIAN
 #      define STRUCT_ENDIAN    BIG_ENDIAN
 #elif BYTE_ORDER == BIG_ENDIAN