linux-kernel - Re: [PATCH v3 5/6] MIPS: Loongson64: SMP: Fix up play

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Date:   Wed, 4 Nov 2020 14:31:49 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Lu Zeng <zenglu@...ngson.cn>, Jun Yi <yijun@...ngson.cn>
Subject: Re: [PATCH v3 5/6] MIPS: Loongson64: SMP: Fix up play_dead jump
 indicator

Hi, all,

On 11/03/2020 03:12 PM, Tiezhu Yang wrote:
> In play_dead function, the whole 64-bit PC mailbox was used as a indicator
> to determine if the master core had written boot jump information.
>
> However, after we introduced CSR mailsend, the hardware will not guarante
> an atomic write for the 64-bit PC mailbox. Thus we have to use the lower
> 32-bit which is written at the last as the jump indicator instead.
>
> Signed-off-by: Lu Zeng <zenglu@...ngson.cn>
> Signed-off-by: Jun Yi <yijun@...ngson.cn>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>
> v2: No changes
> v3: Update the commit message and comment
>
>   arch/mips/loongson64/smp.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/loongson64/smp.c b/arch/mips/loongson64/smp.c
> index 736e98d..aa0cd72 100644
> --- a/arch/mips/loongson64/smp.c
> +++ b/arch/mips/loongson64/smp.c
> @@ -764,9 +764,10 @@ static void loongson3_type3_play_dead(int *state_addr)
>   		"1: li    %[count], 0x100             \n" /* wait for init loop */
>   		"2: bnez  %[count], 2b                \n" /* limit mailbox access */
>   		"   addiu %[count], -1                \n"
> -		"   ld    %[initfunc], 0x20(%[base])  \n" /* get PC via mailbox */
I have some confusion here. Play_dead CPUs is always brought up by cpu_up().
On Loongson64, it calls loongson3_boot_secondary(). The value of 
startargs[0]
is the address of smp_bootstrap() which is in CKSEG0 and a constant 
after the
kernel is compiled. That means its value likes 0xffffffff8... and only 
the low
32bit is useful. As "lw" is sign-extended, could we replace "ld" with 
"lw" simply?

Thanks,
Jinyang
> +		"   lw    %[initfunc], 0x20(%[base])  \n" /* check lower 32-bit as jump indicator */
>   		"   beqz  %[initfunc], 1b             \n"
>   		"   nop                               \n"
> +		"   ld    %[initfunc], 0x20(%[base])  \n" /* get PC (whole 64-bit) via mailbox */
>   		"   ld    $sp, 0x28(%[base])          \n" /* get SP via mailbox */
>   		"   ld    $gp, 0x30(%[base])          \n" /* get GP via mailbox */
>   		"   ld    $a1, 0x38(%[base])          \n"