linux-kernel - Re: [PATCH v1] dd: Invoke one probe retry cycle after some initcall levels

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Date:   Fri, 07 Sep 2018 13:34:30 -0700
From:   rishabhb@...eaurora.org
To:     rafael@...nel.org
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        psodagud@...eaurora.org, ckadabi@...eaurora.org,
        tsoni@...eaurora.org, linux-pm@...r.kernel.org,
        Vikram Mulukutla <markivx@...eaurora.org>
Subject: Re: [PATCH v1] dd: Invoke one probe retry cycle after some initcall
 levels

On 2018-08-13 10:39, Rishabh Bhatnagar wrote:
> From: Rishabh Bhatnagar <rishabhb@...eaurora.org>
> 
> Drivers that are registered at an initcall level may have to
> wait until late_init before the probe deferral mechanism can
> retry their probe functions. It is possible that their
> dependencies were resolved much earlier, in some cases even
> before the next initcall level. Invoke one probe retry cycle
> at every _sync initcall level after subsys initcall, allowing
> these drivers to be probed earlier.
> To give an example many Qualcomm drivers are dependent on the
> regulator and bus driver. Both the regulator and bus driver
> are probed in the subsys_initcall level. Now the probe of bus
> driver requires regulator to be working. If the probe of bus
> driver happens before regulator, then bus driver's probe will
> be deferred and all other device's probes which depend on bus
> driver will also be deferred.
> The impact of this problem is reduced if we have this patch.
> 
> Signed-off-by: Vikram Mulukutla <markivx@...eaurora.org>
> Signed-off-by: Rishabh Bhatnagar <rishabhb@...eaurora.org>
> ---
> 
> Changes since v0:
>  * Remove arch_initcall_sync(deferred_probe_initcall) from patch. This 
> is not
>    really needed as none of the devices are re-probed in 
> arch_initcall_sync
>    level.
> 
>  drivers/base/dd.c | 32 ++++++++++++++++++++++++++------
>  1 file changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 1435d72..9aa41aa 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -224,23 +224,43 @@ void device_unblock_probing(void)
>  	driver_deferred_probe_trigger();
>  }
> 
> +static void enable_trigger_defer_cycle(void)
> +{
> +	driver_deferred_probe_enable = true;
> +	driver_deferred_probe_trigger();
> +	/*
> +	 * Sort as many dependencies as possible before the next initcall
> +	 * level
> +	 */
> +	flush_work(&deferred_probe_work);
> +}
> +
>  /**
>   * deferred_probe_initcall() - Enable probing of deferred devices
>   *
>   * We don't want to get in the way when the bulk of drivers are 
> getting probed.
>   * Instead, this initcall makes sure that deferred probing is delayed 
> until
> - * late_initcall time.
> + * all the registered initcall functions at a particular level are 
> completed.
> + * This function is invoked at every *_initcall_sync level.
>   */
>  static int deferred_probe_initcall(void)
>  {
> -	driver_deferred_probe_enable = true;
> -	driver_deferred_probe_trigger();
> -	/* Sort as many dependencies as possible before exiting initcalls */
> -	flush_work(&deferred_probe_work);
> +	enable_trigger_defer_cycle();
> +	driver_deferred_probe_enable = false;
> +	return 0;
> +}
> +subsys_initcall_sync(deferred_probe_initcall);
> +fs_initcall_sync(deferred_probe_initcall);
> +device_initcall_sync(deferred_probe_initcall);
> +
> +static int deferred_probe_enable_fn(void)
> +{
> +	/* Enable deferred probing for all time */
> +	enable_trigger_defer_cycle();
>  	initcalls_done = true;
>  	return 0;
>  }
> -late_initcall(deferred_probe_initcall);
> +late_initcall(deferred_probe_enable_fn);
> 
>  /**
>   * device_is_bound() - Check if device is bound to a driver

Hi Rafael
Just a reminder about this patch. Let me know if you want me to add/edit 
anything else.
-Rishabh