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

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, May 07, 2019 at 04:33:31PM +0530, Vinod Koul wrote:
> On 07-05-19, 07:54, Greg KH wrote:
> > On Tue, May 07, 2019 at 10:57:32AM +0530, Vinod Koul wrote:
> > > On 06-05-19, 21:24, Pierre-Louis Bossart wrote:
> > > > 
> > > > > > +int sdw_sysfs_bus_init(struct sdw_bus *bus)
> > > > > > +{
> > > > > > +	struct sdw_master_sysfs *master;
> > > > > > +	int err;
> > > > > > +
> > > > > > +	if (bus->sysfs) {
> > > > > > +		dev_err(bus->dev, "SDW sysfs is already initialized\n");
> > > > > > +		return -EIO;
> > > > > > +	}
> > > > > > +
> > > > > > +	master = kzalloc(sizeof(*master), GFP_KERNEL);
> > > > > > +	if (!master)
> > > > > > +		return -ENOMEM;
> > > > > 
> > > > > Why are you creating a whole new device to put all of this under?  Is
> > > > > this needed?  What will the sysfs tree look like when you do this?  Why
> > > > > can't the "bus" device just get all of these attributes and no second
> > > > > device be created?
> > > > 
> > > > I tried a quick hack and indeed we could simplify the code with something as
> > > > simple as:
> > > > 
> > > > [attributes omitted]
> > > > 
> > > > static const struct attribute_group sdw_master_node_group = {
> > > > 	.attrs = master_node_attrs,
> > > > 	.name = "mipi-disco"
> > > > };
> > > > 
> > > > int sdw_sysfs_bus_init(struct sdw_bus *bus)
> > > > {
> > > > 	return sysfs_create_group(&bus->dev->kobj, &sdw_master_node_group);
> > > > }
> > > > 
> > > > void sdw_sysfs_bus_exit(struct sdw_bus *bus)
> > > > {
> > > > 	sysfs_remove_group(&bus->dev->kobj, &sdw_master_node_group);	
> > > > }
> > > > 
> > > > which gives me a simpler structure and doesn't require additional
> > > > pretend-devices:
> > > > 
> > > > /sys/bus/acpi/devices/PRP00001:00/int-sdw.0/mipi-disco# ls
> > > > clock_gears
> > > > /sys/bus/acpi/devices/PRP00001:00/int-sdw.0/mipi-disco# more clock_gears
> > > > 8086
> > > > 
> > > > The issue I have is that for the _show() functions, I don't see a way to go
> > > > from the device argument to bus. In the example above I forced the output
> > > > but would need a helper.
> > > > 
> > > > static ssize_t clock_gears_show(struct device *dev,
> > > > 				struct device_attribute *attr, char *buf)
> > > > {
> > > > 	struct sdw_bus *bus; // this is what I need to find from dev
> > > > 	ssize_t size = 0;
> > > > 	int i;
> > > > 
> > > > 	return sprintf(buf, "%d \n", 8086);
> > > > }
> > > > 
> > > > my brain is starting to fry, but I don't see how container_of() would work
> > > > here since the bus structure contains a pointer to the device. I don't also
> > > > see a way to check for all devices for the bus_type soundwire.
> > > > For the slaves we do have a macro based on container_of(), so wondering if
> > > > we made a mistake in the bus definition? Vinod, any thoughts?
> > > 
> > > yeah I dont recall a way to get bus fed into create_group, I did look at
> > > the other examples back then and IIRC and most of them were using a
> > > global to do the trick (I didn't want to go down that route).
> > > 
> > > I think that was the reason I wrote it this way...
> > > 
> > > BTW if you do use psedo-device you can create your own struct foo which
> > > embeds device and then then you can use container approach to get foo
> > > (and foo contains bus as a member).
> > > 
> > > Greg, any thoughts?
> > 
> > Why would you have "bus" attributes on a device?  I don't think you are
> > using "bus" here like the driver model uses the term "bus", right?
> > 
> > What are you really trying to show here?
> > 
> > And if you need to know the bus pointer from the device, why don't you
> > have a pointer to it in your device-specific structure?
> 
> 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.

thanks,

greg k-h