[Skiboot] [PATCH] opal/hmi: Fix a TOD HMI failure during a race condition.

[Ananth N Mavinakayanahalli]

On Sat, Aug 13, 2016 at 06:41:11PM +0530, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh at linux.vnet.ibm.com>
> 
> There are chances where another interrupt can wake a CPU in 0x100
> vector just when HMI for TOD error is also pending. In such a rare race
> condition if CPU has woken up with tb_loss power saving mode, it will
> invoke opal call to resync the TB. Since TOD is already in error state,
> resync TB will timeout leaving TFMR bit 18 set to '1'. (TFMR[18]=1 means
> TB is prepared to receive new value from TOD. Once the new value is
> received this bit gets reset to '0', otherwise TB would stay in waiting
> state). When HMI is delivered, it may find all TFMR errors are already
> cleared but would fail to restore TB since TFMR bit 18 is already set.
> This leads to HMI recovery failure causing a kernel crash.
> 
> This patch fixes this by clearing of TB errors if TFMR[18] is set to 1.
> This makes sure that TB is in clean state before TB restore process starts.

Does this need to go into older firmware release updates if there are
any?

Ananth