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SubjectRe: [PATCH v1] of: platform: Batch fwnode parsing in the init_machine() path
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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@android.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@grygorii-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

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