Re: [PULL 48/48] hw/timer/armv7m_systick: Rewrite to use ptimers

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 11/4/20 11:03 AM, Andrew Jones wrote:
> On Tue, Oct 27, 2020 at 11:44:38AM +0000, Peter Maydell wrote:
>> The armv7m systick timer is a 24-bit decrementing, wrap-on-zero,
>> clear-on-write counter. Our current implementation has various
>> bugs and dubious workarounds in it (for instance see
>> https://bugs.launchpad.net/qemu/+bug/1872237).
>>
>> We have an implementation of a simple decrementing counter
>> and we put a lot of effort into making sure it handles the
>> interesting corner cases (like "spend a cycle at 0 before
>> reloading") -- ptimer.
>>
>> Rewrite the systick timer to use a ptimer rather than
>> a raw QEMU timer.
>>
>> Unfortunately this is a migration compatibility break,
>> which will affect all M-profile boards.
>>
>> Among other bugs, this fixes
>> https://bugs.launchpad.net/qemu/+bug/1872237 :
>> now writes to SYST_CVR when the timer is enabled correctly
>> do nothing; when the timer is enabled via SYST_CSR.ENABLE,
>> the ptimer code will (because of POLICY_NO_IMMEDIATE_RELOAD)
>> arrange that after one timer tick the counter is reloaded
>> from SYST_RVR and then counts down from there, as the
>> architecture requires.
>>
>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> Message-id: 20201015151829.14656-3-peter.maydell@linaro.org
>> ---
>>  include/hw/timer/armv7m_systick.h |   3 +-
>>  hw/timer/armv7m_systick.c         | 124 +++++++++++++-----------------
>>  2 files changed, 54 insertions(+), 73 deletions(-)
>>
> 
> Do we also need something like the diff below now?
> 
> 
> diff --git a/hw/arm/Kconfig b/hw/arm/Kconfig
> index fdf4464b9484..7d5d89e1acf9 100644
> --- a/hw/arm/Kconfig
> +++ b/hw/arm/Kconfig
> @@ -291,6 +291,7 @@ config ZYNQ
>  
>  config ARM_V7M
>      bool
> +    select PTIMER

Oops yes indeed.

>  
>  config ALLWINNER_A10
>      bool
> 
> 
> Thanks,
> drew
> 
>