[PATCH AUTOSEL for 4.4 100/167] powerpc/[booke|4xx]: Don't clobber TCR[WP] when setting TCR[DIE]

Sasha Levin
2018-03-19T16:10:18Z

From: Ivan Mikhaylov <ivan@de.ibm.com>

[ Upstream commit 6e2f03e292ef46eed2b31b0a344a91d514f9cd81 ]

Prevent a kernel panic caused by unintentionally clearing TCR watchdog
bits. At this point in the kernel boot, the watchdog may have already
been enabled by u-boot. The original code's attempt to write to the TCR
register results in an inadvertent clearing of the watchdog
configuration bits, causing the 476 to reset.

Signed-off-by: Ivan Mikhaylov <ivan@de.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
arch/powerpc/kernel/time.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 1be1092c7204..9baba9576e99 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -686,12 +686,20 @@ static int __init get_freq(char *name, int cells, unsigned long *val)
static void start_cpu_decrementer(void)
{
#if defined(CONFIG_BOOKE) || defined(CONFIG_40x)
+ unsigned int tcr;
+
/* Clear any pending timer interrupts */
mtspr(SPRN_TSR, TSR_ENW | TSR_WIS | TSR_DIS | TSR_FIS);

- /* Enable decrementer interrupt */
- mtspr(SPRN_TCR, TCR_DIE);
-#endif /* defined(CONFIG_BOOKE) || defined(CONFIG_40x) */
+ tcr = mfspr(SPRN_TCR);
+ /*
+ * The watchdog may have already been enabled by u-boot. So leave
+ * TRC[WP] (Watchdog Period) alone.
+ */
+ tcr &= TCR_WP_MASK; /* Clear all bits except for TCR[WP] */
+ tcr |= TCR_DIE; /* Enable decrementer */
+ mtspr(SPRN_TCR, tcr);
+#endif
}

void __init generic_calibrate_decr(void)
--
2.14.1