linux-kernel - Re: [PATCH] MIPS: BMIPS: Disable pref 30 for buggy CPUs

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Date:   Fri, 31 Jul 2020 11:05:26 +0200
From:   Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-mips@...ux-mips.org,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <linux-mips@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: BMIPS: Disable pref 30 for buggy CPUs

On Thu, Jul 30, 2020 at 09:24:01PM -0700, Florian Fainelli wrote:
> Disable pref 30 by utilizing the standard quirk method and matching the
> affected SoCs: 7344, 7346, 7425.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  arch/mips/bmips/setup.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/arch/mips/bmips/setup.c b/arch/mips/bmips/setup.c
> index 19308df5f577..df0efea12611 100644
> --- a/arch/mips/bmips/setup.c
> +++ b/arch/mips/bmips/setup.c
> @@ -110,6 +110,20 @@ static void bcm6368_quirks(void)
>  	bcm63xx_fixup_cpu1();
>  }
>  
> +static void bmips5000_pref30_quirk(void)
> +{
> +	__asm__ __volatile__(
> +	"	li	$8, 0x5a455048\n"
> +	"	.word	0x4088b00f\n"	/* mtc0 $8, $22, 15 */
> +	"	nop; nop; nop\n"
> +	"	.word	0x4008b008\n"	/* mfc0 $8, $22, 8 */
> +	/* disable "pref 30" on buggy CPUs */
> +	"	lui	$9, 0x0800\n"
> +	"	or	$8, $9\n"
> +	"	.word	0x4088b008\n"	/* mtc0 $8, $22, 8 */
> +	: : : "$8", "$9");

what's the reason for not using mfc/mtc here ?

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]