[RFC PATCH] async: Add cmdline option to specify drivers to be async probed

From: Feng Tang
Date: Fri Jan 25 2019 - 08:20:04 EST

Asynchronous driver probing can help much on kerenl 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 family of HWs, some of which
could use async probling 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 discussed at

* 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, which prevents these spi/i2c controller drivers to be async
probed. For plaforms not using these spi/i2c slave devices, they can
use this cmdline option to benefit from the async probing.

Suggested-by: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Signed-off-by: Feng Tang <feng.tang@xxxxxxxxx>
drivers/base/dd.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 8ac10af..1f257561 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 */
+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.
@@ -674,8 +678,26 @@ 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);
+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!");
+ strlcpy(async_probe_drv_names, buf, ASYNC_DRV_NAMES_MAX_LEN - 1);
+ return 0;
+__setup("driver_async_probe=", save_async_options);
bool driver_allows_async_probing(struct device_driver *drv)
+ if (unlikely(cmdline_requested_async_probing(drv->name)))
+ return true;
switch (drv->probe_type) {
return true;