linux-kernel - Re: [PATCH v4 1/4] ARM: UniPhier: add basic support for UniPhier architecture

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Date:	Thu, 23 Apr 2015 12:41:08 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Olof Johansson <olof@...om.net>, devicetree@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v4 1/4] ARM: UniPhier: add basic support for UniPhier architecture

Hi Heiko,


2015-04-21 23:56 GMT+09:00 Heiko Stübner <heiko@...ech.de>:
> Am Dienstag, 21. April 2015, 16:21:27 schrieb Masahiro Yamada:
>> Initial commit for a new SoC family, UniPhier, developed by
>> Socionext Inc. (formerly, System LSI Business Division of
>> Panasonic Corporation).
>>
>> This commit includes a minimal set of components for booting the
>> kernel, including SMP support.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> ---
>
> [...]
>
>> +static int uniphier_boot_secondary(unsigned int cpu,
>> +                                struct task_struct *idle)
>> +{
>> +     struct regmap *sbcm_regmap;
>> +     int ret;
>> +
>> +     sbcm_regmap = syscon_regmap_lookup_by_compatible(
>> +                     "socionext,uniphier-system-bus-controller-misc");
>> +     if (IS_ERR(sbcm_regmap)) {
>> +             pr_err("failed to regmap system-bus-controller-misc\n");
>> +             return PTR_ERR(sbcm_regmap);
>> +     }
>> +
>> +     ret = regmap_write(sbcm_regmap, 0x1208,
>> +                        virt_to_phys(uniphier_secondary_startup));
>> +     if (!ret)
>> +             asm("sev"); /* wake up secondary CPU */
>> +
>> +     return ret;
>> +}
>> +
>> +struct smp_operations uniphier_smp_ops __initdata = {
>> +     .smp_prepare_cpus       = uniphier_smp_prepare_cpus,
>> +     .smp_boot_secondary     = uniphier_boot_secondary,
>> +};
>
> this is more of a drive-by comment, but you're doing the syscon lookup on
> every boot of a core, which includes walking big parts of the devicetree every
> time.
>
> Is there anything speaking against doing this once in a .smp_prepare_cpus
> callback?

Not really.

I fixed this in v5.
Thanks for reviewing my patch!


-- 
Best Regards
Masahiro Yamada
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