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SubjectRe: [PATCH v2 5/6] MIPS: Loongson64: Make sure the PC address is correct when 3A4000+ CPU hotplug
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在 2020/11/3 11:15, Tiezhu Yang 写道:
> In loongson3_type3_play_dead(), in order to make sure the PC address is
> correct, use lw to read the low 32 bits first, if the result is not zero,
> then use ld to read the whole 64 bits, otherwise there maybe exists atomic
> problem due to write high 32 bits first and then low 32 bits, like this:
>
> high 32 bits (write done)
> -- only read high 32-bits which is wrong
> low 32 bits (not yet write done)
>
> This problem is especially for Loongson 3A4000+ CPU due to using Mail_Send
> register which can only send 32 bits data one time. Although it is hard to
> reproduce, we can do something at the software level to avoid the risks for
> 3A4000+ CPU, this change has no influence on the other Loongson CPUs.
>
> Signed-off-by: Lu Zeng <zenglu@loongson.cn>
> Signed-off-by: Jun Yi <yijun@loongson.cn>
> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>

Hi Tiezhu,

Sorry that I didn't look this patch carefully in previous rev, here's my
comments,

Firstly the commit message and code comment looks bogus...

I'd prefer

---
MIPS: Loongson64: SMP: Fix up play_dead jump indicator

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 64-bit PC mailbox won't be
written atomicly. Thus we have to use the lower 32-bit, which will be
written at
the last, as the jump indicator instead.
--

Thanks.

> ---
>
> v2: No changes
>
> 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..e32b46e 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 */
> + " lw %[initfunc], 0x20(%[base]) \n" /* get PC (low 32 bits) via mailbox */

Here you can comment as "Check jump indicator (lower 32-bit of PC mailbox)"

Thanks.

- Jiaxun
> " beqz %[initfunc], 1b \n"
> " nop \n"
> + " ld %[initfunc], 0x20(%[base]) \n" /* get PC (whole 64 bits) 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"

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