linux-kernel - Re: [PATCH v1] of: platform: Batch fwnode parsing in the init

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Date:   Fri, 2 Oct 2020 21:11:21 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Saravana Kannan <saravanak@...gle.com>
CC:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux-OMAP <linux-omap@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Tony Lindgren <tony@...mide.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] of: platform: Batch fwnode parsing in the
 init_machine() path



On 02/10/2020 20:48, Saravana Kannan wrote:
> On Fri, Oct 2, 2020 at 8:03 AM 'Grygorii Strashko' via kernel-team
> <kernel-team@...roid.com> wrote:
>>
>>
>>
>> On 02/10/2020 14:40, Grygorii Strashko wrote:
>>>
>>>
>>> On 02/10/2020 02:19, Laurent Pinchart wrote:
>>>> Hi Saravana,
>>>>
>>>> Thank you for the patch.
>>>>
>>>> On Thu, Oct 01, 2020 at 03:59:51PM -0700, Saravana Kannan wrote:
>>>>> When commit 93d2e4322aa7 ("of: platform: Batch fwnode parsing when
>>>>> adding all top level devices") optimized the fwnode parsing when all top
>>>>> level devices are added, it missed out optimizing this for platform
>>>>> where the top level devices are added through the init_machine() path.
>>>>>
>>>>> This commit does the optimization for all paths by simply moving the
>>>>> fw_devlink_pause/resume() inside of_platform_default_populate().
>>>>
>>>> Based on v5.9-rc5, before the patch:
>>>>
>>>> [    0.652887] cpuidle: using governor menu
>>>> [   12.349476] No ATAGs?
>>>>
>>>> After the patch:
>>>>
>>>> [    0.650460] cpuidle: using governor menu
>>>> [   12.262101] No ATAGs?
>>>>
>>>> :-(
>>>
>>> This is kinda expected :( because omap2 arch doesn't call of_platform_default_populate()
>>>
>>> Call path:
>>> board-generic.c
>>>    DT_MACHINE_START()
>>>      .init_machine    = omap_generic_init,
>>>
>>>    omap_generic_init()
>>>      pdata_quirks_init(omap_dt_match_table);
>>>           of_platform_populate(NULL, omap_dt_match_table,
>>>                    omap_auxdata_lookup, NULL);
>>>
>>> Other affected platforms
>>> arm: mach-ux500
>>> some mips
>>> some powerpc
>>>
>>> there are also case when a lot of devices placed under bus node, in such case
>>>    of_platform_populate() calls from bus drivers will also suffer from this issue.
>>>
>>> I think one option could be to add some parameter to _populate() or introduce new api.
>>>
>>> By the way, is there option to disable this feature at all?
>>> Is there Kconfig option?
>>> Is there any reasons why such complex and time consuming code added to the kernel and not implemented on DTC level?
>>>
>>>
>>> Also, I've came with another diff, pls check.
>>>
>>> [    0.000000] Booting Linux on physical CPU 0x0
>>> [    0.000000] Linux version 5.9.0-rc6-01791-g9acba6b38757-dirty (grygorii@...gorii-XPS-13-9370) (arm-linux-gnueabihf-gcc (GNU Toolcha0
>>> [    0.000000] CPU: ARMv7 Processor [412fc0f2] revision 2 (ARMv7), cr=10c5387d
>>> [    0.000000] CPU: div instructions available: patching division code
>>> [    0.000000] CPU: PIPT / VIPT nonaliasing data cache, PIPT instruction cache
>>> [    0.000000] OF: fdt: Machine model: TI AM5718 IDK
>>> ...
>>> [    0.053443] cpuidle: using governor ladder
>>> [    0.053470] cpuidle: using governor menu
>>> [    0.089304] No ATAGs?
>>> ...
>>> [    3.092291] devtmpfs: mounted
>>> [    3.095804] Freeing unused kernel memory: 1024K
>>> [    3.100483] Run /sbin/init as init process
>>>
>>>
>>>
>>> ------ >< ---
>>> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>>> index 071f04da32c8..4521b26e7745 100644
>>> --- a/drivers/of/platform.c
>>> +++ b/drivers/of/platform.c
>>> @@ -514,6 +514,12 @@ static const struct of_device_id reserved_mem_matches[] = {
>>>           {}
>>>    };
>>>
>>> +static int __init of_platform_fw_devlink_pause(void)
>>> +{
>>> +       fw_devlink_pause();
>>> +}
>>> +core_initcall(of_platform_fw_devlink_pause);
>>> +
>>>    static int __init of_platform_default_populate_init(void)
>>>    {
>>>           struct device_node *node;
>>> @@ -538,9 +544,7 @@ static int __init of_platform_default_populate_init(void)
>>>           }
>>>
>>>           /* Populate everything else. */
>>> -       fw_devlink_pause();
>>>           of_platform_default_populate(NULL, NULL, NULL);
>>> -       fw_devlink_resume();
>>>
>>>           return 0;
>>>    }
>>> @@ -548,6 +552,7 @@ arch_initcall_sync(of_platform_default_populate_init);
>>>
>>>    static int __init of_platform_sync_state_init(void)
>>>    {
>>> +       fw_devlink_resume();
>>
>> ^ it seems has to be done earlier, like
>> +static int __init of_platform_fw_devlink_resume(void)
>> +{
>> +       fw_devlink_resume();
>> +       return 0;
>> +}
>> +device_initcall_sync(of_platform_fw_devlink_resume);
> 
> This will mean no device will probe until device_initcall_sync().
> Unfortunately, I don't think we can make such a sweeping assumption.

Could you answer below questions, pls?
>>> By the way, is there option to disable this feature at all?
>>> Is there Kconfig option?

-- 
Best regards,
grygorii