Re: [PATCH 0/3] Convert ppc and microblaze devices to new ptimer API

[Peter Maydell]

On Thu, 17 Oct 2019 at 14:21, Peter Maydell <address@hidden> wrote:
>
> This patchset converts the devices used by ppc and microblaze
> machines to the new ptimer API. (xilinx_timer is used by both,
> hence putting both archs in the same patchset).
>
> Currently the ptimer design uses a QEMU bottom-half as its mechanism
> for calling back into the device model using the ptimer when the
> timer has expired.  Unfortunately this design is fatally flawed,
> because it means that there is a lag between the ptimer updating its
> own state and the device callback function updating device state, and
> guest accesses to device registers between the two can return
> inconsistent device state. This was reported as a bug in a specific
> timer device but it's a problem with the generic ptimer code:
> https://bugs.launchpad.net/qemu/+bug/1777777
>
> The updates to the individual ptimer devices are straightforward:
> we need to add begin/commit calls around the various places that
> modify the ptimer state, and use the new ptimer_init() function
> to create the timer.
>
> Testing has been 'make check' only, which obviously doesn't
> exercise the devices very much, so more specific testing would
> be appreciated. I'm happy for these patches to go in via the
> ppc tree if you want, or I can collect them up with the other
> ptimer-related changes I'm sending for other archs.

I'll put these in via target-arm.next, since they've all
been reviewed now and nobody's suggested a preference
for some other route.

thanks
-- PMM