Re: [PATCH] soundwire: bus: add enumerated slave to device list

[Pierre-Louis Bossart]

On 9/9/20 10:54 AM, Srinivas Kandagatla wrote:
> On 09/09/2020 15:39, Pierre-Louis Bossart wrote:
> > > > > Currently slave devices are only added either from device tree or acpi
> > > > > entries. However lets say, there is wrong or no entry of a slave 
> > > > > device
> > > > > in DT that is enumerated, then there is no way for user to know all
> > > > > the enumerated devices on the bus.
> > > >
> > > > Sorry Srinivas, I don't understand your point.
> > > >
> > > > The sysfs entries will include all devices that are described in 
> > > > platform firmware (be it DT or ACPI).
> > >
> > > yes that is true, but it will not include all the enumerated devices 
> > > on the bus!
> > >
> > > In my case on a new board I was trying to figure out what devices are 
> > > on the bus even before even adding any device tree entries!
> >
> > We've seen this before but dynamic debug provides all the information 
> > you need. see e.g. the logs from 
> > https://sof-ci.01.org/linuxpr/PR2425/build4447/devicetest/
> >
> > jf-cml-rvp-sdw-1 kernel: [  289.751974] soundwire sdw-master-0: Slave 
> > attached, programming device number
> > jf-cml-rvp-sdw-1 kernel: [  289.752121] soundwire sdw-master-0: SDW 
> > Slave Addr: 10025d070000 <<< HERE
>
> Yes, I have noticed this too! This will be printed for every call to 
> sdw_extract_slave_id()!
>
> ...
> > Now I get your point but
> > a) you already have a dynamic debug trace to list all devices
> > b) adding 'undeclared' devices would make things quite murky and is 
> > only half of the solution. We already struggle because we already have 
> > 'ghost' devices in sysfs that are not physically present, and no way 
> > to differentiate between the two. If we did add those entries, then 
> > we'd need two new sysfs attributes such as
> > 'declared' and 'enumerated'.
>
> I totally agree with you on dealing with the undeclared devices, which 
> is unnecessary mess!

It's not necessarily that bad.
- if the intent is to have a single platform firmware that can deal with 
different boards, it's a good thing.
- but if it's just sloppy platform firmware that just does copy-paste 
from platform to platform then indeed it becomes a mess.

> May be we could make the enumerated devices discovery bit more verbose!

Maybe adding a device number sysfs entry would help, e.g. reporting
NotAttched or a value in [0,11] would tell you if the device is actually 
present.