Re: [alsa-devel] [RFC PATCH 1/7] soundwire: Add sysfs support for master(s)

[Pierre-Louis Bossart]

On 5/8/19 4:16 AM, Greg KH wrote:
> On Wed, May 08, 2019 at 01:16:06PM +0530, Vinod Koul wrote:
> > On 07-05-19, 17:49, Pierre-Louis Bossart wrote:
> > > > > The model here is that Master device is PCI or Platform device and then
> > > > > creates a bus instance which has soundwire slave devices.
> > > > >
> > > > > So for any attribute on Master device (which has properties as well and
> > > > > representation in sysfs), device specfic struct (PCI/platfrom doesn't
> > > > > help). For slave that is not a problem as sdw_slave structure takes care
> > > > > if that.
> > > > >
> > > > > So, the solution was to create the psedo sdw_master device for the
> > > > > representation and have device-specific structure.
> > > >
> > > > Ok, much like the "USB host controller" type device.  That's fine, make
> > > > such a device, add it to your bus, and set the type correctly.  And keep
> > > > a pointer to that structure in your device-specific structure if you
> > > > really need to get to anything in it.
> > >
> > > humm, you lost me on the last sentence. Did you mean using
> > > set_drv/platform_data during the init and retrieving the bus information
> > > with get_drv/platform_data as needed later? Or something else I badly need
> > > to learn?
> >
> > IIUC Greg meant we should represent a soundwire master device type and
> > use that here. Just like we have soundwire slave device type. Something
> > like:
> >
> > struct sdw_master {
> >          struct device dev;
> >          struct sdw_master_prop *prop;
> >          ...
> > };
> >
> > In show function you get master from dev (container of) and then use
> > that to access the master properties. So int.sdw.0 can be of this type.
>
> Yes, you need to represent the master device type if you are going to be
> having an internal representation of it.

Humm, confused...In the existing code bus and master are synonyms, see 
e.g. following code excerpts:

 * sdw_add_bus_master() - add a bus Master instance
 * @bus: bus instance
 *
 * Initializes the bus instance, read properties and create child
 * devices.

struct sdw_bus {
	struct device *dev; <<< pointer here
	unsigned int link_id;
	struct list_head slaves;
	DECLARE_BITMAP(assigned, SDW_MAX_DEVICES);
	struct mutex bus_lock;
	struct mutex msg_lock;
	const struct sdw_master_ops *ops;
	const struct sdw_master_port_ops *port_ops;
	struct sdw_bus_params params;
	struct sdw_master_prop prop;

The existing code creates a platform_device in 
drivers/soundwire/intel_init.c, and it's assigned by the following code:

static int intel_probe(struct platform_device *pdev)
{
	struct sdw_cdns_stream_config config;
	struct sdw_intel *sdw;
	int ret;

	sdw = devm_kzalloc(&pdev->dev, sizeof(*sdw), GFP_KERNEL);
[snip]
	sdw->cdns.dev = &pdev->dev;
	sdw->cdns.bus.dev = &pdev->dev;

I really don't see what you are hinting at, sorry, unless we are talking 
about major surgery in the code.