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

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Date:   Fri, 2 Oct 2020 14:40:14 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Saravana Kannan <saravanak@...gle.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        <geert+renesas@...der.be>, <gregkh@...uxfoundation.org>,
        <linux-omap@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <peter.ujfalusi@...com>, <rjw@...ysocki.net>,
        <tomi.valkeinen@...com>, <tony@...mide.com>,
        <ulf.hansson@...aro.org>, <kernel-team@...roid.com>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] of: platform: Batch fwnode parsing in the
 init_machine() path



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();
         device_links_supplier_sync_state_resume();
         return 0;
  }



-- 
Best regards,
grygorii