Re: [PATCH v2 0/3] Convert sparc devices to new ptimer API

[Peter Maydell]

On Mon, 21 Oct 2019 at 14:43, Peter Maydell <address@hidden> wrote:
>
> This patchset converts the devices used by sparc machines to the new
> ptimer API.
>
> 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.
>
> Changes v1->v2:
>  * patches 2 and 3 are the old 1 and 2 and have been reviewed
>  * patch 1 is new and removes a pointless NULL check; without
>    this we'd probably have got Coverity errors when patch 3
>    added a use of t->timer before the check for it being NULL

I'm going to apply these to target-arm.next; I know they haven't
been on list long but the change since v1 is only minor and
they've all been reviewed.

thanks
-- PMM