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

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Date:   Fri, 19 May 2017 20:30:06 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Ivan Mikhaylov <ivan@...ibm.com>,
        Alistair Popple <alistair@...ple.id.au>,
        Matt Porter <mporter@...nel.crashing.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Joel Stanley <joel@...abs.au.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 4/4] arch/powerpc/44x/fsp2: wdt tcr update instead of
 whole rewrite

On Mon, 2017-05-15 at 16:07 +0300, Ivan Mikhaylov wrote:
> +#ifdef CONFIG_FSP2
> +       /*
> +        * Prevent a kernel panic caused by unintentionally clearing TCR
> +        * watchdog bits.  At this point in the kernel boot, the watchdog has
> +        * 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 440 to reset.
> +        */
> +       tcr = mfspr(SPRN_TCR);
> +       tcr &= TCR_WP_MASK; /* clear all bits except for TCR[WP] */
> +       tcr |= TCR_DIE; /* enable decrementer */
> +       mtspr(SPRN_TCR, tcr);
> +#else

This should be a runtime test, not a compile time option.

Cheers,
Ben.