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

Pierre-Louis Bossart
2019-05-07T02:24:21Z

>> +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?