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 <[email protected]>
> Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
> Message-id: [email protected]
> ---
> 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
config ALLWINNER_A10
bool
Thanks,
drew
