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Subject: Re: [PATCH] MIPS: BMIPS: Disable pref 30 for buggy CPUs
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Florian Fainelli <f.fainelli@gmail.com>,
        linux-mips@linux-mips.org
Cc:     Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        "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>
 <21ad5472-1287-acba-5604-09f2e633c043@flygoat.com>
From:   Florian Fainelli <f.fainelli@gmail.com>
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Message-ID: <46de49ec-cc8b-708a-0cdd-82389b041078@gmail.com>
Date:   Fri, 31 Jul 2020 15:49:28 -0700
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On 7/31/20 3:34 AM, Jiaxun Yang wrote:
> 
> 
> 在 2020/7/31 下午12:24, Florian Fainelli 写道:
>> 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");
>> +}
> Hi,
> 
> Is there any toolchain issue blocking read_c0_**** family helpers being
> used?
> 
> Use .word looks unreasonable.

Yes, the assembler would be choking on the custom $22 selector, however
this patch should not be necessary given that the boot loader (CFE)
should have long been updated by now to disable pref 30.

Thanks
-- 
Florian