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

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Message-ID: <20190507052732.GD16052@vkoul-mobl>
Date:   Tue, 7 May 2019 10:57:32 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, alsa-devel@...a-project.org,
        tiwai@...e.de, linux-kernel@...r.kernel.org,
        liam.r.girdwood@...ux.intel.com, broonie@...nel.org,
        srinivas.kandagatla@...aro.org, jank@...ence.com, joe@...ches.com,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [RFC PATCH 1/7] soundwire: Add sysfs support for
 master(s)

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?

Thanks
-- 
~Vinod