On 7/29/22 12:15, Greg Kroah-Hartman wrote: > On Fri, Jul 29, 2022 at 11:46:32AM -0500, Pierre-Louis Bossart wrote: >> >>>>>>> That should be fine, tools should just be looking for the attributes, >>>>>>> not the existance of a directory, right? >>>>>> >>>>>> The idea what that we would only expose ports that actually exist. >>>>>> That's helpful information anyone with a basic knowledge of the >>>>>> SoundWire specification would understand. >>>>> >>>>> Is "dp0" a port? If so, why isn't it a real device? >>>> >>>> The SoundWire spec defines the concept of 'data port'. The valid ranges >>>> are 1..14, but in all existing devices the number of data ports is way >>>> smaller, typically 2 to 4. Data ports (DPn) are source or sink, and >>>> there's no firm rule that data ports needs to be contiguous. >>>> >>>> DP0 is a 'special case' where the data transport is used for control >>>> information, e.g. programming large set of registers or firmware >>>> download. DP0 is completely optional in hardware, and not handled in >>>> Linux for now. >>>> >>>> DP0 and DPn expose low-level transport registers, which define how the >>>> contents of a FIFO will be written or read from the bus. Think of it as >>>> a generalization of the concept of TDM slots, where instead of having a >>>> fixed slot per frame the slot position/repetition/runlength can be >>>> programmed. >>>> >>>> The data ports could be as simple as 1-bit PDM, or support 8ch PCM >>>> 24-bits. That's the sort of information reported in attributes. >>> >>> Why not make them a real device like we do for USB endpoints? >> >> I don't see what adding another layer of hierarchy would bring. In their >> simplest configuration, there are 6 registers 8-bit exposed. And the >> port registers, when present, are accessed with a plain vanilla offset. > > Who uses these registers? The bus layer. When a 'stream' is created, the 'bit allocation' will define who owns which bitSlots in the frame and the registers will be programmed. The bit allocation may be dynamic or fixed depending on the host. >>> What uses these sysfs files today that would be confused about an empty >>> directory? >> >> That's a good question. I am not aware of any tools making use of those >> attributes. To a large degree, they are helpful only for debug and >> support, all these read-only attributes could be moved to debugfs. That >> could be a way to simplify everyone's life.... > > That would be much nicer, put it all in a single debugfs file and it > would be so simple. > > What attributes could we do that for? All of them really - except maybe the device number which could be used to figure what the device is when looking at power status and other 'standard' sysfs attributes. sdw:3:025d:0714:01 is not really user-friendly, device_number 1 is.
