From: Thomas Huth <thuth@redhat.com>

When writing to this register, QEMU currently aborts:

 $ echo "readl 0x10000018" | ./qemu-system-arm -audiodev none,id=snd0 \
    -M integratorcp,accel=qtest,audiodev=snd0 -display none -qtest stdio
 [I 0.000000] OPENED
 [R +0.001907] readl 0x10000018
 qemu: hardware error: integratorcm_read: CM_LMBUSCNT
 [...]
 Aborted                    (core dumped)

This is bad, a guest should ideally never be able to kill QEMU like this.

Now, according to the "Intergrator/CP User Guide" from:

 https://developer.arm.com/documentation/dui0159/b/porting-integrator-ap-and-im-pd1/registers

 "The Integrator/AP CM_LMBUSCNT has been removed."

That means this register does not seem to be implemented on real CP boards
at all, only for older AP boards. Thus it should be fine if we simply
ignore this register in QEMU and handle it like all other unimplemented
registers in the "default" handler of the case statement.

Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3407
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 hw/arm/integratorcp.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/hw/arm/integratorcp.c b/hw/arm/integratorcp.c
index 0bf519b6bb8..28d478eb52b 100644
--- a/hw/arm/integratorcp.c
+++ b/hw/arm/integratorcp.c
@@ -107,9 +107,6 @@ static uint64_t integratorcm_read(void *opaque, hwaddr offset,
         } else {
             return s->cm_lock;
         }
-    case 6: /* CM_LMBUSCNT */
-        /* ??? High frequency timer.  */
-        hw_error("integratorcm_read: CM_LMBUSCNT");
     case 7: /* CM_AUXOSC */
         return s->cm_auxosc;
     case 8: /* CM_SDRAM */
-- 
2.53.0

On 20/4/26 08:49, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> When writing to this register, QEMU currently aborts:
> 
>   $ echo "readl 0x10000018" | ./qemu-system-arm -audiodev none,id=snd0 \
>      -M integratorcp,accel=qtest,audiodev=snd0 -display none -qtest stdio
>   [I 0.000000] OPENED
>   [R +0.001907] readl 0x10000018
>   qemu: hardware error: integratorcm_read: CM_LMBUSCNT
>   [...]
>   Aborted                    (core dumped)
> 
> This is bad, a guest should ideally never be able to kill QEMU like this.
> 
> Now, according to the "Intergrator/CP User Guide" from:
> 
>   https://developer.arm.com/documentation/dui0159/b/porting-integrator-ap-and-im-pd1/registers
> 
>   "The Integrator/AP CM_LMBUSCNT has been removed."
> 
> That means this register does not seem to be implemented on real CP boards
> at all, only for older AP boards. Thus it should be fine if we simply
> ignore this register in QEMU and handle it like all other unimplemented
> registers in the "default" handler of the case statement.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3407
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   hw/arm/integratorcp.c | 3 ---
>   1 file changed, 3 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>