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From: Huacai Chen <chenhuacai@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Huacai Chen <chenhuacai@loongson.cn>,
	Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Airlie <airlied@linux.ie>, Jonathan Corbet <corbet@lwn.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Xuefeng Li <lixuefeng@loongson.cn>,
	Yanteng Si <siyanteng@loongson.cn>,
	Jiaxun Yang <jiaxun.yang@flygoat.com>
Subject: Re: [PATCH V3 20/22] LoongArch: Add multi-processor (SMP) support
Date: Sat, 18 Sep 2021 15:22:57 +0800	[thread overview]
Message-ID: <CAAhV-H4C2ZDO4P_Xy8ic_wjmT7PHNCDfrKKQRZw-A4tgr6Y=aw@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a0N=SA-E7ChrMrA5Gv6TDMzJ4_QNUN5OzpJWgzyJwcboA@mail.gmail.com>

Hi, Arnd,

On Fri, Sep 17, 2021 at 5:57 PM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Sep 17, 2021 at 5:57 AM Huacai Chen <chenhuacai@loongson.cn> wrote:
>
> > +
> > +struct task_struct;
> > +
> > +struct plat_smp_ops {
> > +       void (*send_ipi_single)(int cpu, unsigned int action);
> > +       void (*send_ipi_mask)(const struct cpumask *mask, unsigned int action);
> > +       void (*smp_setup)(void);
> > +       void (*prepare_cpus)(unsigned int max_cpus);
> > +       int (*boot_secondary)(int cpu, struct task_struct *idle);
> > +       void (*init_secondary)(void);
> > +       void (*smp_finish)(void);
> > +#ifdef CONFIG_HOTPLUG_CPU
> > +       int (*cpu_disable)(void);
> > +       void (*cpu_die)(unsigned int cpu);
> > +#endif
> > +};
>
>
> Do you foresee having more than one implementation of these in the
> near future? If not, I would suggest leaving out the extra indirection
> and just using direct function calls.
OK, let me rethink this, if it is still needed, I will tell you why.

>
> > +#ifdef CONFIG_SMP
> > +
> > +static inline void plat_smp_setup(void)
> > +{
> > +       extern const struct plat_smp_ops *mp_ops;       /* private */
> > +
> > +       mp_ops->smp_setup();
> > +}
> > +
> > +#else /* !CONFIG_SMP */
> > +
> > +static inline void plat_smp_setup(void) { }
> > +
> > +#endif /* !CONFIG_SMP */
>
> You could even go further and do what arch/arm64 has, making
> SMP support unconditional. This obviously depends on hardware
> roadmaps, but if all harfdware you support has multiple cores,
> then non-SMP mode just adds complexity.
As mentioned in another patch, we do have some MCU hardware (no FP, no
SMP, and even no MMU).

>
> > +
> > +#define MAX_CPUS 64
>
> You CONFIG_NR_CPUS allows up to 256. I think you need to
> adjust one of the numbers to match the other, or remove this
> definition and just use CONFIG_NR_CPUS directly.
Legacy IPI method only supports at most 64 CPUs (limited by the MMIO
register space). Maybe we can remove the whole legacy method support,
then we can remove MAX_CPUS, too.
>
> > +
> > +static volatile void *ipi_set_regs[MAX_CPUS];
> > +static volatile void *ipi_clear_regs[MAX_CPUS];
> > +static volatile void *ipi_status_regs[MAX_CPUS];
> > +static volatile void *ipi_en_regs[MAX_CPUS];
> > +static volatile void *ipi_mailbox_buf[MAX_CPUS];
>
> Why are these 'volatile'? If they are MMIO registers, they
> should be __iomem, and accessed using readl()/writel()
>  etc
Yes, they are MMIO registers and __iomem is needed.

Huacai
>
>        Arnd

  reply	other threads:[~2021-09-18  7:23 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-17  3:57 [PATCH V3 00/22] arch: Add basic LoongArch support Huacai Chen
2021-09-17  3:57 ` [PATCH V3 01/22] Documentation: LoongArch: Add basic documentations Huacai Chen
2021-09-23 20:37   ` Pavel Machek
2021-09-24  4:07     ` Huacai Chen
2021-09-23 20:59   ` Pavel Machek
2021-09-24  4:10     ` Huacai Chen
2021-09-24  6:58       ` Pavel Machek
2021-09-24  7:31         ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 02/22] Documentation/zh_CN: Add basic LoongArch documentations Huacai Chen
2021-09-17  3:57 ` [PATCH V3 03/22] LoongArch: Add elf-related definitions Huacai Chen
2021-09-17  3:57 ` [PATCH V3 04/22] LoongArch: Add writecombine support for drm Huacai Chen
2021-09-17  3:57 ` [PATCH V3 05/22] LoongArch: Add build infrastructure Huacai Chen
2021-09-17  7:53   ` Arnd Bergmann
2021-09-18  4:35     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 06/22] LoongArch: Add CPU definition headers Huacai Chen
2021-09-17  3:57 ` [PATCH V3 07/22] LoongArch: Add atomic/locking headers Huacai Chen
2021-09-17  3:57 ` [PATCH V3 08/22] LoongArch: Add other common headers Huacai Chen
2021-09-17  3:57 ` [PATCH V3 09/22] LoongArch: Add boot and setup routines Huacai Chen
2021-09-17  8:11   ` Arnd Bergmann
2021-09-18  4:54     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 10/22] LoongArch: Add exception/interrupt handling Huacai Chen
2021-09-17  3:57 ` [PATCH V3 11/22] LoongArch: Add process management Huacai Chen
2021-09-17  3:57 ` [PATCH V3 12/22] LoongArch: Add memory management Huacai Chen
2021-09-17  3:57 ` [PATCH V3 13/22] LoongArch: Add system call support Huacai Chen
2021-09-17  8:24   ` Arnd Bergmann
2021-09-18  6:55     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 14/22] LoongArch: Add signal handling support Huacai Chen
2021-09-17  8:26   ` Arnd Bergmann
2021-09-17 21:10   ` Eric W. Biederman
2021-09-18  7:12     ` Huacai Chen
2021-09-19  9:58       ` Arnd Bergmann
2021-09-20  2:36         ` Huacai Chen
2021-09-20 21:14           ` Richard Henderson
2021-09-22  2:43             ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 15/22] LoongArch: Add elf and module support Huacai Chen
2021-09-17  8:28   ` Arnd Bergmann
2021-09-18  7:14     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 16/22] LoongArch: Add misc common routines Huacai Chen
2021-09-17  6:10   ` Christoph Hellwig
2021-09-17  6:36     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 17/22] LoongArch: Add some library functions Huacai Chen
2021-09-17  8:33   ` Arnd Bergmann
2021-09-18  7:16     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 18/22] LoongArch: Add PCI controller support Huacai Chen
2021-09-17  9:02   ` Arnd Bergmann
2021-09-18  7:36     ` Huacai Chen
2021-09-21 22:36       ` Bjorn Helgaas
2021-09-22 15:33         ` Arnd Bergmann
2021-09-17  3:57 ` [PATCH V3 19/22] LoongArch: Add VDSO and VSYSCALL support Huacai Chen
2021-09-17  3:57 ` [PATCH V3 20/22] LoongArch: Add multi-processor (SMP) support Huacai Chen
2021-09-17  9:57   ` Arnd Bergmann
2021-09-18  7:22     ` Huacai Chen [this message]
2021-09-17  3:57 ` [PATCH V3 21/22] LoongArch: Add Non-Uniform Memory Access (NUMA) support Huacai Chen
2021-09-17  6:15   ` Christoph Hellwig
2021-09-17  6:40     ` Huacai Chen
2021-09-17  3:57 ` [PATCH V3 22/22] LoongArch: Add Loongson-3 default config file Huacai Chen
2021-09-17  9:59 ` [PATCH V3 00/22] arch: Add basic LoongArch support Arnd Bergmann

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