Who calls “probe” function in driver code?

Question

I am trying to understand this driver code of mcspi for omap2 panda board.

I don't understand who calls the probe function and what is the call chain in this driver code?

How does the driver is informed when the device is connected?

Answer 1

The probe function from spi-omap2-mcspi.c is saved in the static struct platform_driver omap2_mcspi_driver, which is registered with module_platform_driver(omap2_mcspi_driver); (at the end of file). The module_platform_driver macro, defined in platform_device.h will pass the struct to platform_driver_register macro and __platform_driver_register function from drivers/base/platform.c

527 /**
528  * __platform_driver_register - register a driver for platform-level devices
529  * @drv: platform driver structure
530  * @owner: owning module/driver
531  */
532 int __platform_driver_register(struct platform_driver *drv,
533                                 struct module *owner)
534 {
...
536         drv->driver.bus = &platform_bus_type;
537         if (drv->probe)
538                 drv->driver.probe = platform_drv_probe;
...
544         return driver_register(&drv->driver);
545 }
546 EXPORT_SYMBOL_GPL(__platform_driver_register);

The probe now passed to driver_register function from drivers/base/driver.c

139 /**
140  * driver_register - register driver with bus
141  * @drv: driver to register
142  *
143  * We pass off most of the work to the bus_add_driver() call,
144  * since most of the things we have to do deal with the bus
145  * structures.
146  */
147 int driver_register(struct device_driver *drv)
148 {
...
154         if ((drv->bus->probe && drv->probe) ||
...
167         ret = bus_add_driver(drv);
...
178 }

So, now the driver is registered in the bus (platform_bus_type).

Actual call to probe is done via driver_probe_device drivers/base/dd.c, then really_probe (same file line 265):

265 static int really_probe(struct device *dev, struct device_driver *drv)
266 {
...
270         pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
271                  drv->bus->name, __func__, drv->name, dev_name(dev));
...
287         if (dev->bus->probe) {
288                 ret = dev->bus->probe(dev);       /// <<<< HERE
289                 if (ret)
290                         goto probe_failed;
291         } else if (drv->probe) {
292                 ret = drv->probe(dev);            /// <<<< OR HERE
293                 if (ret)
294                         goto probe_failed;
295         }
296 
297         driver_bound(dev);
298         ret = 1;
299         pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
300                  drv->bus->name, __func__, dev_name(dev), drv->name);
301         goto done;