Re: [Qemu-devel] [PATCH v1 3/3] armv7m_systick: abort instead of locking on a bad rate

[KONRAD Frederic <frederic.konrad@adacore.com>]

On 06/29/2017 02:43 PM, Peter Maydell wrote:
> On 29 June 2017 at 13:35, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>> This is true it is better to abort here than risking a deadlock.
>>
>> However it seems to me they are 3 issues here:
>> - the deadlock pattern is caused by using a global variable,
>> - stellaris:ssys_calculate_system_clock() no checking RCC.SYSDIV and
>> RCC2.SYSDIV2 values <= 2 are reserved (GUEST_ERROR)
>> - stellaris:ssys_write(RCC2) not overrides correctly RCC
> 
> Stellaris works fine. It's other ARMv7M boards (which might forget
> to set system_clock_scale) which don't work.

Yes actually the issue is with new boards when you forgot to set
system_clock_scale (as it happened to me :)).

Peter you suggest we fix that later when the clock is in place?

Fred

> 
>> I'd rather take this opportunity to fix the deadlock pattern using a
>> getter/setter on system_clock_scale, doing the zero check in the setter and
>> eventually aborting in the getter, what do you think?
> 
> We should be using a clock property on the CPU instead of system_clock_scale.
> Unfortunately Konrad's series attempting to add that infrastructure
> is still in the "trying to sort out the right API in code review"
> stage. I don't think it's worth trying to fiddle with the API
> for it before we have the right eventual infrastructure in place.
> 
> (What system_clock_scale is actually doing is setting the
> emulated frequency of the CPU, since that affects the
> frequency of the timer.)
> 
> thanks
> -- PMM
>