[PATCH 1/3] dm: core: Add DM_FLAG_PROBE_AFTER_BIND flag

[Sean Anderson]

On 4/22/22 7:07 PM, Marek Vasut wrote:
> On 4/23/22 00:45, Sean Anderson wrote:
>> On 4/22/22 9:52 AM, Marek Vasut wrote:
>>> On 4/22/22 15:49, Sean Anderson wrote:
>>>> On 4/22/22 9:15 AM, Marek Vasut wrote:
>>>>> Introduce DM_FLAG_PROBE_AFTER_BIND flag, which can be set by driver or
>>>>> uclass in .bind(), to indicate such driver instance should be probe()d
>>>>> once binding of all devices is complete.
>>>>>
>>>>> This is useful in case the driver determines that hardware initialization
>>>>> is mandatory on boot, and such initialization happens only in probe().
>>>>> This also solves the inability to call device_probe() from .bind().
>>>>
>>>> So why not add an init_leds function to init_sequence_r?
>>>
>>> Because this flag is generic solution and not hack specific to LEDs.
>>
>> Isn't init_sequence_r the generic solution?
> 
> No, init_sequence_r is just a list of functions that gets called early on during boot to bring U-Boot up. One of the functions is initr_dm(), DM init, which brings up the driver model. The init_sequence_r has nothing to do with driver binding or probing though, that's the DM job.
> 
>> Every device gets probed that way (or directly as a result of a command).
> 
> No device probe gets triggered via init_sequence_r.
> There are many ad-hoc device_probe() calls in the various init_sequence_r function implementation,

Every device in U-Boot is probed in one of three ways

- As a dependency of another device (clocks, pinmuxes, gpios, etc.)
- Directly on the command line (most boot devices)
- From an init_sequence (timers, watchdogs, serial, PCI, gpio hogs, etc.)

The goal of course being to minimize the amount of probed devices. This of course requires having
some things at the "root" of the tree. In Linux, everything bound is probed until nothing more can
be probed. In that sense, under Linux everything is the "root" of the tree. But for U-Boot the
second two options specify the "roots."

Some of the things in init_sequence are ad-hoc, especially the non-DM stuff. LEDs are pretty ad-hoc,
last I checked, but that's mainly because there are 2-3 separate non-DM ways to control LEDs.

> but that's all there because there is no better way to implement that within the DM framework so far. Now there is, with this flag, so those workarounds can also be cleaned up.

This *is* within the DM framework. Adding a flag which is set on bound devices has the same effect
as dm_mux_init does when called from initr_dm_devices. The only difference is implementation. So
why is this better?

--Sean