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Message-ID: <20150826224213.GC10582@home.buserror.net>
Date: Wed, 26 Aug 2015 17:42:13 -0500
From: Scott Wood <scottwood@...escale.com>
To: Chenhui Zhao <chenhui.zhao@...escale.com>
CC: <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>,
<Jason.Jin@...escale.com>
Subject: Re: [PATCH v2,5/5] PowerPC/mpc85xx: Add CPU hotplug support for E6500
On Wed, Aug 26, 2015 at 08:09:48PM +0800, Chenhui Zhao wrote:
> + .globl booting_thread_hwid
> +booting_thread_hwid:
> + .long INVALID_THREAD_HWID
> + .align 3
The commit message goes into no detail about the changes you're making to
thread handling, nor are there relevant comments.
> +/*
> + * r3 = the thread physical id
> + */
> +_GLOBAL(book3e_stop_thread)
> + li r4, 1
> + sld r4, r4, r3
> + mtspr SPRN_TENC, r4
> + isync
> + blr
Why did the C code not have an isync, if it's required here?
> _GLOBAL(fsl_secondary_thread_init)
> /* Enable branch prediction */
> lis r3,BUCSR_INIT@h
> @@ -197,8 +236,10 @@ _GLOBAL(fsl_secondary_thread_init)
> * but the low bit right by two bits so that the cpu numbering is
> * continuous.
> */
> - mfspr r3, SPRN_PIR
> - rlwimi r3, r3, 30, 2, 30
> + bl 10f
> +10: mflr r5
> + addi r5,r5,(booting_thread_hwid - 10b)
> + lwz r3,0(r5)
> mtspr SPRN_PIR, r3
> #endif
I assume the reason for this is that, unlike the kexec case, the cpu has
been reset so PIR has been reset? Don't make me guess -- document.
> @@ -245,6 +286,30 @@ _GLOBAL(generic_secondary_smp_init)
> mr r3,r24
> mr r4,r25
> bl book3e_secondary_core_init
> +
> +/*
> + * If we want to boot Thread1, start Thread1 and stop Thread0.
> + * Note that only Thread0 will run the piece of code.
> + */
What ensures that only thread 0 runs this? Especially if we're entering
via kdump on thread 1?
s/the piece/this piece/
> + LOAD_REG_ADDR(r3, booting_thread_hwid)
> + lwz r4, 0(r3)
> + cmpwi r4, INVALID_THREAD_HWID
> + beq 20f
> + cmpw r4, r24
> + beq 20f
Do all cores get released from the spin table before the first thread
gets kicked?
> +
> + /* start Thread1 */
> + LOAD_REG_ADDR(r5, fsl_secondary_thread_init)
> + ld r4, 0(r5)
> + li r3, 1
> + bl book3e_start_thread
> +
> + /* stop Thread0 */
> + li r3, 0
> + bl book3e_stop_thread
> +10:
> + b 10b
> +20:
> #endif
>
> generic_secondary_common_init:
> diff --git a/arch/powerpc/platforms/85xx/smp.c b/arch/powerpc/platforms/85xx/smp.c
> index 73eb994..61f68ad 100644
> --- a/arch/powerpc/platforms/85xx/smp.c
> +++ b/arch/powerpc/platforms/85xx/smp.c
> @@ -181,17 +181,11 @@ static inline u32 read_spin_table_addr_l(void *spin_table)
> static void wake_hw_thread(void *info)
> {
> void fsl_secondary_thread_init(void);
> - unsigned long imsr1, inia1;
> - int nr = *(const int *)info;
> + unsigned long inia;
> + int hw_cpu = get_hard_smp_processor_id(*(const int *)info);
>
> - imsr1 = MSR_KERNEL;
> - inia1 = *(unsigned long *)fsl_secondary_thread_init;
> -
> - mttmr(TMRN_IMSR1, imsr1);
> - mttmr(TMRN_INIA1, inia1);
> - mtspr(SPRN_TENS, TEN_THREAD(1));
> -
> - smp_generic_kick_cpu(nr);
> + inia = *(unsigned long *)fsl_secondary_thread_init;
> + book3e_start_thread(cpu_thread_in_core(hw_cpu), inia);
> }
> #endif
>
> @@ -279,7 +273,6 @@ static int smp_85xx_kick_cpu(int nr)
> int ret = 0;
> #ifdef CONFIG_PPC64
> int primary = nr;
> - int primary_hw = get_hard_smp_processor_id(primary);
> #endif
>
> WARN_ON(nr < 0 || nr >= num_possible_cpus());
> @@ -287,33 +280,43 @@ static int smp_85xx_kick_cpu(int nr)
> pr_debug("kick CPU #%d\n", nr);
>
> #ifdef CONFIG_PPC64
> + booting_thread_hwid = INVALID_THREAD_HWID;
> /* Threads don't use the spin table */
> - if (cpu_thread_in_core(nr) != 0) {
> - int primary = cpu_first_thread_sibling(nr);
> + if (threads_per_core == 2) {
> + booting_thread_hwid = get_hard_smp_processor_id(nr);
What does setting booting_thread_hwid to INVALID_THREAD_HWID here
accomplish? If threads_per_core != 2 it would never have been set to
anything else, and if threads_per_core == 2 you immediately overwrite it.
> + primary = cpu_first_thread_sibling(nr);
>
> if (WARN_ON_ONCE(!cpu_has_feature(CPU_FTR_SMT)))
> return -ENOENT;
>
> - if (cpu_thread_in_core(nr) != 1) {
> - pr_err("%s: cpu %d: invalid hw thread %d\n",
> - __func__, nr, cpu_thread_in_core(nr));
> - return -ENOENT;
> - }
> -
> - if (!cpu_online(primary)) {
> - pr_err("%s: cpu %d: primary %d not online\n",
> - __func__, nr, primary);
> - return -ENOENT;
> + /*
> + * If either one of threads in the same core is online,
> + * use the online one to start the other.
> + */
> + if (qoriq_pm_ops)
> + qoriq_pm_ops->cpu_up_prepare(nr);
cpu_up_prepare does rcpm_v2_cpu_exit_state(cpu, E500_PM_PH20). How do
you know the cpu is already in PH20? What if this is initial boot? Are
you relying on it being a no-op in that case?
> +
> + if (cpu_online(primary)) {
> + smp_call_function_single(primary,
> + wake_hw_thread, &nr, 1);
> + goto done;
> + } else if (cpu_online(primary + 1)) {
> + smp_call_function_single(primary + 1,
> + wake_hw_thread, &nr, 1);
> + goto done;
> }
>
> - smp_call_function_single(primary, wake_hw_thread, &nr, 0);
> - return 0;
> + /* If both threads are offline, continue to star primary cpu */
s/star/start/
> + } else if (threads_per_core > 2) {
> + pr_err("Do not support more than 2 threads per CPU.");
WARN_ONCE(1, "More than 2 threads per core not supported: %d\n",
threads_per_core);
-Scott
--
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