linux-kernel - Re: [PATCH v3] async: Add cmdline option to specify drivers to be async probed

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Date:   Wed, 30 Jan 2019 08:27:55 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Feng Tang <feng.tang@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] async: Add cmdline option to specify drivers to be
 async probed

On 1/29/19 11:23 PM, Feng Tang wrote:
> Asynchronous driver probing can help much on kernel fastboot, and
> this option can provide a flexible way to optimize and quickly verify
> async driver probe.
> 
> Also it will help in below cases:
> * Some driver actually covers several families of HWs, some of which
>   could use async probing while others don't. So we can't simply
>   turn on the PROBE_PREFER_ASYNCHRONOUS flag in driver, but use this
>   cmdline option, like igb driver async patch discussed at
>   https://www.spinics.net/lists/netdev/msg545986.html
> 
> * For SOC (System on Chip) with multiple spi or i2c controllers, most
>   of the slave spi/i2c devices will be assigned with fixed controller
>   number, while async probing may make those controllers get different
>   index for each boot, which prevents those controller drivers to be
>   async probed. For platforms not using these spi/i2c slave devices,
>   they can use this cmdline option to benefit from the async probing.
> 
> Suggested-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> ---
> Changelog:
>   v3: 
>      move the cmdline_requested_async_probing() into "default:"
>      part to enforce the PROBE_FORCE_SYNCHRONOUS check, as suggested
>      by Alexander Duyck
>     
>   v2:
>     * change Alexander Duyck's email to alexander.h.duyck@...ux.intel.com
>     * fix the parameter for strlcpy()
> 
>  drivers/base/dd.c | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 8ac10af..e99d781 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -57,6 +57,10 @@ static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
>  static struct dentry *deferred_devices;
>  static bool initcalls_done;
>  
> +/* Save the async probe drivers' name from kernel cmdline */
> +#define ASYNC_DRV_NAMES_MAX_LEN	256
> +static char async_probe_drv_names[ASYNC_DRV_NAMES_MAX_LEN];
> +
>  /*
>   * In some cases, like suspend to RAM or hibernation, It might be reasonable
>   * to prohibit probing of devices as it could be unsafe.
> @@ -674,6 +678,22 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
>  	return ret;
>  }
>  
> +static inline bool cmdline_requested_async_probing(const char *drv_name)
> +{
> +	return parse_option_str(async_probe_drv_names, drv_name);
> +}
> +
> +/* The format is like driver_async_probe=drv_name1,drv_name2,drv_name3 */

Please document this boot option in Documentation/admin-guide/kernel-parameters.txt.

> +static int __init save_async_options(char *buf)
> +{
> +	if (strlen(buf) >= ASYNC_DRV_NAMES_MAX_LEN)
> +		printk(KERN_WARNING "Too long list for async_probe_drv_names!\n");

use the correct cmdline option name here.  E.g.:
		printk(KERN_WARNING "Too long list of driver names for 'driver_async_probe'\n");

> +
> +	strlcpy(async_probe_drv_names, buf, ASYNC_DRV_NAMES_MAX_LEN);
> +	return 0;
> +}
> +__setup("driver_async_probe=", save_async_options);
> +
>  bool driver_allows_async_probing(struct device_driver *drv)
>  {
>  	switch (drv->probe_type) {
> @@ -684,6 +704,9 @@ bool driver_allows_async_probing(struct device_driver *drv)
>  		return false;
>  
>  	default:
> +		if (cmdline_requested_async_probing(drv->name))
> +			return true;
> +
>  		if (module_requested_async_probing(drv->owner))
>  			return true;
>  
> 


-- 
~Randy