Re: [PATCH 4/4] arch/powerpc/44x/fsp2: wdt tcr update instead of whole rewrite

From: Michael Ellerman
Date: Fri May 26 2017 - 06:37:32 EST


Michael Ellerman <mpe@xxxxxxxxxxxxxx> writes:

> Ivan Mikhaylov <ivan@xxxxxxxxxx> writes:
>>
>> From my point of view it's possible. I've checked docu and on idea
>> it should be possible cause WP is only affecting watchdog ping time.
>
> The question is, is there any chance that leaving those bits set on
> another platform will cause a problem?
>
> ie. on existing machines we always clear those bits, is it OK that we
> will now start leaving those bits with whatever value they had.

I came up with the patch below (more or less your v2), if it breaks
something we can always fix it.

cheers

commit c80409358a9c91e1f6b18353dad939b851bb3522
Author: Ivan Mikhaylov <ivan@xxxxxxxxxx>
Date: Fri May 19 18:47:05 2017 +0300

powerpc/[booke|4xx]: Don't clobber TCR[WP] when setting TCR[DIE]

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@xxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 2b33cfaac7b8..60714b8c9a2f 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -739,12 +739,20 @@ 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)