Thanks for the quick review Srinivas,
This patch in general is missing device tree support for both matching and uevent so this will not clearly work for Qualcomm controller unless we do via platform bus, which does not sound right!
see other email, the platform bus is handled by a platform device/driver. There was no intention to change that, it's by design rather than an omission/error.
+/**
- sdw_master_device_startup() - startup hardware
- @md: Linux Soundwire master device
- This use of this function is optional. It is only needed if the
- hardware cannot be started during a driver probe, e.g. due to power
- rail dependencies. The implementation is platform-specific but the
- bus will typically go through a hardware-reset sequence and devices
- will be enumerated once they report as ATTACHED.
- */
+int sdw_master_device_startup(struct sdw_master_device *md) +{ + struct sdw_master_driver *mdrv; + struct device *dev; + int ret = 0;
+ if (IS_ERR_OR_NULL(md)) + return -EINVAL;
+ dev = &md->dev; + mdrv = drv_to_sdw_master_driver(dev->driver);
+ if (mdrv && mdrv->startup) + ret = mdrv->startup(md);
+ return ret; +} +EXPORT_SYMBOL_GPL(sdw_master_device_startup);
Who would call this function? and How would it get hold of master device instance ?
sdw_master_device_add() returns a struct_master_device *md, so the parent has a handle to that device. See the device creation here:
https://github.com/thesofproject/linux/blob/9c7487b33072040ab755d32ca173b751...
This startup() would be called by the parent when all requirements/dependencies are met. Put differently, it allows the probe to run much earlier and check for platform firmware information (which links are enabled, what devices are exposed by platform firmware), while the startup is really when the bus clk/data lines will start toggling.
https://github.com/thesofproject/linux/blob/9c7487b33072040ab755d32ca173b751...
and the call from the SOF layer is here:
https://github.com/thesofproject/linux/blob/9c7487b33072040ab755d32ca173b751...
Again, if everything is ready at probe time there's no need to delay the actual bus startup. This is not needed for Qualcomm platforms where the Master device is part of a codec. It's actually irrelevant since there is no driver, so the startup callback does not even exist :-)
How would soundwire core also ensure that we do not actively use this master if it is not ready. Similar comment for shutdown callback.
That's a fair point, we could add a state variable and a check that the probe happened before.
In practice the two cases of device creation and startup are different phases so it'd more of a paranoia check.
Thanks, -Pierre