[RFC] hw/arm/armv7m: Expose and access System Control Space as little endian

Commit Message

Philippe Mathieu-Daudé Sept. 24, 2024, 7:19 p.m. UTC

Per the Armv7-M Architecture Reference Manual (ARM DDI 0403E):

  The System Control Space (SCS, address range 0xE000E000 to
  0xE000EFFF) is a memory-mapped 4KB address space that provides
  32-bit registers for configuration, status reporting and control.
  All accesses to the SCS are little endian.

Expose the region as a little-endian one and force dispatched
accesses to also be in little endianness.

Fixes: d5d680cacc ("memory: Access MemoryRegion with endianness")
Signed-off-by: Philippe Mathieu-Daudé <[e-mail]>
---
 hw/arm/armv7m.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

Comments

Peter Maydell Sept. 25, 2024, 11:04 a.m. UTC | #1

On Tue, 24 Sept 2024 at 20:19, Philippe Mathieu-Daudé <[e-mail]> wrote:
>
> Per the Armv7-M Architecture Reference Manual (ARM DDI 0403E):
>
>   The System Control Space (SCS, address range 0xE000E000 to
>   0xE000EFFF) is a memory-mapped 4KB address space that provides
>   32-bit registers for configuration, status reporting and control.
>   All accesses to the SCS are little endian.
>
> Expose the region as a little-endian one and force dispatched
> accesses to also be in little endianness.
>
> Fixes: d5d680cacc ("memory: Access MemoryRegion with endianness")
> Signed-off-by: Philippe Mathieu-Daudé <[e-mail]>

What's the rationale for this change? All Arm system emulator
builds are TARGET_LITTLE_ENDIAN, so MO_TE and MO_LE have
identical behaviour, as do DEVICE_LITTLE_ENDIAN and
DEVICE_TARGET_ENDIAN.

thanks
-- PMM

Patch

diff --git a/hw/arm/armv7m.c b/hw/arm/armv7m.c
index 7c68525a9e..4a01b970e6 100644
--- a/hw/arm/armv7m.c
+++ b/hw/arm/armv7m.c
@@ -140,7 +140,7 @@  static MemTxResult v7m_sysreg_ns_write(void *opaque, hwaddr addr,
         /* S accesses to the alias act like NS accesses to the real region */
         attrs.secure = 0;
         return memory_region_dispatch_write(mr, addr, value,
-                                            size_memop(size) | MO_TE, attrs);
+                                            size_memop(size) | MO_LE, attrs);
     } else {
         /* NS attrs are RAZ/WI for privileged, and BusFault for user */
         if (attrs.user) {
@@ -160,7 +160,7 @@  static MemTxResult v7m_sysreg_ns_read(void *opaque, hwaddr addr,
         /* S accesses to the alias act like NS accesses to the real region */
         attrs.secure = 0;
         return memory_region_dispatch_read(mr, addr, data,
-                                           size_memop(size) | MO_TE, attrs);
+                                           size_memop(size) | MO_LE, attrs);
     } else {
         /* NS attrs are RAZ/WI for privileged, and BusFault for user */
         if (attrs.user) {
@@ -174,7 +174,7 @@  static MemTxResult v7m_sysreg_ns_read(void *opaque, hwaddr addr,
 static const MemoryRegionOps v7m_sysreg_ns_ops = {
     .read_with_attrs = v7m_sysreg_ns_read,
     .write_with_attrs = v7m_sysreg_ns_write,
-    .endianness = DEVICE_NATIVE_ENDIAN,
+    .endianness = DEVICE_LITTLE_ENDIAN,
 };
 
 static MemTxResult v7m_systick_write(void *opaque, hwaddr addr,
@@ -187,7 +187,7 @@  static MemTxResult v7m_systick_write(void *opaque, hwaddr addr,
     /* Direct the access to the correct systick */
     mr = sysbus_mmio_get_region(SYS_BUS_DEVICE(&s->systick[attrs.secure]), 0);
     return memory_region_dispatch_write(mr, addr, value,
-                                        size_memop(size) | MO_TE, attrs);
+                                        size_memop(size) | MO_LE, attrs);
 }
 
 static MemTxResult v7m_systick_read(void *opaque, hwaddr addr,
@@ -199,14 +199,14 @@  static MemTxResult v7m_systick_read(void *opaque, hwaddr addr,
 
     /* Direct the access to the correct systick */
     mr = sysbus_mmio_get_region(SYS_BUS_DEVICE(&s->systick[attrs.secure]), 0);
-    return memory_region_dispatch_read(mr, addr, data, size_memop(size) | MO_TE,
-                                       attrs);
+    return memory_region_dispatch_read(mr, addr, data,
+                                       size_memop(size) | MO_LE, attrs);
 }
 
 static const MemoryRegionOps v7m_systick_ops = {
     .read_with_attrs = v7m_systick_read,
     .write_with_attrs = v7m_systick_write,
-    .endianness = DEVICE_NATIVE_ENDIAN,
+    .endianness = DEVICE_LITTLE_ENDIAN,
 };
 
 /*