Re: [PATCH v2 2/7] i3c: Add core I3C infrastructure

[Boris Brezillon]

On Mon, 26 Feb 2018 21:40:32 +0100
Boris Brezillon <boris.brezillon@xxxxxxxxxxx> wrote:

> On Mon, 26 Feb 2018 21:36:07 +0100
> Boris Brezillon <boris.brezillon@xxxxxxxxxxx> wrote:
> 
> > > >>> +
> > > >>> +/**
> > > >>> + * struct i3c_master_controller_ops - I3C master methods
> > > >>> + * @bus_init: hook responsible for the I3C bus initialization. This
> > > >>> + *	      initialization should follow the steps described in the I3C
> > > >>> + *	      specification. This hook is called with the bus lock held in
> > > >>> + *	      write mode, which means all _locked() helpers can safely be
> > > >>> + *	      called from there
> > > >>> + * @bus_cleanup: cleanup everything done in
> > > >>> + *		 &i3c_master_controller_ops->bus_init(). This function is
> > > >>> + *		 optional and should only be implemented if
> > > >>> + *		 &i3c_master_controller_ops->bus_init() attached private data
> > > >>> + *		 to I3C/I2C devices. This hook is called with the bus lock
> > > >>> + *		 held in write mode, which means all _locked() helpers can
> > > >>> + *		 safely be called from there
> > > >>> + * @supports_ccc_cmd: should return true if the CCC command is supported, false
> > > >>> + *		      otherwise
> > > >>> + * @send_ccc_cmd: send a CCC command
> > > >>> + * @send_hdr_cmds: send one or several HDR commands. If there is more than one
> > > >>> + *		   command, they should ideally be sent in the same HDR
> > > >>> + *		   transaction
> > > >>> + * @priv_xfers: do one or several private I3C SDR transfers
> > > >>> + * @i2c_xfers: do one or several I2C transfers
> > > >>> + * @request_ibi: attach an IBI handler to an I3C device. This implies defining
> > > >>> + *		 an IBI handler and the constraints of the IBI (maximum payload
> > > >>> + *		 length and number of pre-allocated slots).
> > > >>> + *		 Some controllers support less IBI-capable devices than regular
> > > >>> + *		 devices, so this method might return -%EBUSY if there's no
> > > >>> + *		 more space for an extra IBI registration
> > > >>> + * @free_ibi: free an IBI previously requested with ->request_ibi(). The IBI
> > > >>> + *	      should have been disabled with ->disable_irq() prior to that
> > > >>> + * @enable_ibi: enable the IBI. Only valid if ->request_ibi() has been called
> > > >>> + *		prior to ->enable_ibi(). The controller should first enable
> > > >>> + *		the IBI on the controller end (for example, unmask the hardware
> > > >>> + *		IRQ) and then send the ENEC CCC command (with the IBI flag set)
> > > >>> + *		to the I3C device
> > > >>> + * @disable_ibi: disable an IBI. First send the DISEC CCC command with the IBI
> > > >>> + *		 flag set and then deactivate the hardware IRQ on the
> > > >>> + *		 controller end
> > > >>> + * @recycle_ibi_slot: recycle an IBI slot. Called every time an IBI has been
> > > >>> + *		      processed by its handler. The IBI slot should be put back
> > > >>> + *		      in the IBI slot pool so that the controller can re-use it
> > > >>> + *		      for a future IBI
> > > >>> + *
> > > >>> + * One of the most important hooks in these ops is
> > > >>> + * &i3c_master_controller_ops->bus_init(). Here is a non-exhaustive list of
> > > >>> + * things that should be done in &i3c_master_controller_ops->bus_init():
> > > >>> + *
> > > >>> + * 1) call i3c_master_set_info() with all information describing the master
> > > >>> + * 2) ask all slaves to drop their dynamic address by sending the RSTDAA CCC
> > > >>> + *    with i3c_master_rstdaa_locked()
> > > >>> + * 3) ask all slaves to disable IBIs using i3c_master_disec_locked()
> > > >>> + * 4) start a DDA procedure by sending the ENTDAA CCC with
> > > >>> + *    i3c_master_entdaa_locked(), or using the internal DAA logic provided by
> > > >>> + *    your controller        
> > > >> You mean SETDASA CCC command?      
> > > > No, I really mean ENTDAA and DAA. By internal DAA logic I mean that
> > > > some controllers are probably automating the whole DAA procedure, while
> > > > others may let the SW control every step.      
> > > My understanding is that i3c_master_entdaa_locked() will trigger the DAA process
> > > and DAA can be done by SETDASA, ENTDAA and later after the bus initialization
> > > with SETNEWDA.    
> > 
> > No. Only ENTDAA can trigger a DAA procedure. SETDASA is here to assign
> > a single dynamic address to a device that already has a static address
> > but no dynamic address yet, and SETNEWDA is here to modify the dynamic
> > address of a device that already has one.
> >   
> > > 
> > > I think the DAA process should be more generic, right now is only made through
> > > the ENTDAA command with (cmd.ndests = 1).
> > > I mean, shouldn't this be made by the core? First doing DAA for the devices
> > > declared and them try do discover the rest of devices on the bus.    
> > 
> > Can you detail a bit more? If the only part you're complaining about is
> > pre-assignment of dynamic addresses with SETDASA when a device is
> > declared in the DT with a reg and dynamic-address property, then yes, I
> > think I can provide an helper for that. But this helper would still have
> > to be called from the master controller driver (from ->bus_init() or
> > after a Hot-Join).
> > 
> > Now, if the question is, is there a way we can automate things even more
> > and completely implement DAA from the core? I doubt it, because the way
> > the core will trigger DAA, expose discovered devices or allow you to
> > declare manually assigned addresses is likely to be
> > controller-dependent.
> > When I designed the framework I took the decision to base my work on the
> > spec rather than focusing on the I3C master controller I had to support
> > (Cadence). This is the reason I decided to keep the interface as simple
> > as possible at the risk of encouraging code-duplication (at first)
> > rather than coming up with an interface that is designed with a single
> > controller in mind and having to break things every time a new
> > controller comes out.
> > 
> > Thank you for you comments, but I'd like to know if some of my design
> > choices are blocking you to support your controller. What I've seen so
> > far is a collection of things that might be relevant to fix (though
> > most of them are subject to interpretation and/or a matter of taste),
> > but nothing that should really block you.  
> 
> Well, that's not entirely true: I agree that something is missing in
> ->priv_xfers() to let the controller know about the device limitations,  
> and this could be a blocking aspect.
> 

And I2C functionalities might differ between I3C master controllers, so
that's also something we should transfer to the I3C master driver
instead of imposing it in the core.

-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com