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Subject: Re: [PATCH] MIPS: BMIPS: Disable pref 30 for buggy CPUs
To:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Florian Fainelli <f.fainelli@gmail.com>
Cc:     linux-mips@linux-mips.org,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <bcm-kernel-feedback-list@broadcom.com>,
        "open list:BROADCOM BMIPS MIPS ARCHITECTURE" 
        <linux-mips@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
References: <20200731042401.22871-1-f.fainelli@gmail.com>
 <20200731090526.GB7946@alpha.franken.de>
From:   Florian Fainelli <f.fainelli@gmail.com>
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Message-ID: <0809b01e-3b36-9d8f-2de1-58b7d649f4c8@gmail.com>
Date:   Fri, 31 Jul 2020 15:49:53 -0700
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On 7/31/20 2:05 AM, Thomas Bogendoerfer wrote:
> 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@gmail.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 ?

See my response to Jiaxun, thanks!
-- 
Florian