linux-kernel - Re: [alsa-devel] [PATCH v5 10/15] soundwire: Add sysfs for SoundWire DisCo properties

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Date:   Fri, 22 Dec 2017 17:13:44 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     ALSA <alsa-devel@...a-project.org>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Sudheer Papothi <spapothi@...eaurora.org>,
        Takashi <tiwai@...e.de>, plai@...eaurora.org,
        LKML <linux-kernel@...r.kernel.org>,
        Pierre <pierre-louis.bossart@...ux.intel.com>,
        patches.audio@...el.com, Mark <broonie@...nel.org>,
        srinivas.kandagatla@...aro.org,
        Sagar Dharia <sdharia@...eaurora.org>, alan@...ux.intel.com
Subject: Re: [alsa-devel] [PATCH v5 10/15] soundwire: Add sysfs for SoundWire
 DisCo properties

On Fri, Dec 22, 2017 at 09:33:44AM +0100, Greg Kroah-Hartman wrote:
> On Fri, Dec 22, 2017 at 01:56:56PM +0530, Vinod Koul wrote:

> > Hey Greg,
> > 
> > So I have spent couple of days on this but don't have a solution.
> > 
> > I can create a subdirectory using dynamic attribute group by giving it a
> > name. Works as advertised:). But I am unable to create subdirectory under
> > newly created subdir. The properties defined by MIPI follow a certain
> > hierarchy so we need subdirectories to represent that.
> 
> Yes, you can't create directories 2 levels deep, sorry, didn't realize
> you wanted to do that.
> 
> > Second issue am facing with these is getting the sdw_bus context. I tried
> > adding it but nothing looks elegant. I tried making sdw_attributes on top of
> > struct attribute and pass around the bus but doesn't seem to work for me.
> > 
> > On the contrary, the current design of creating kobjects looked more
> > cleaner. It has been used in bunch of other places, I double checked ref
> > counting and cleanup looks okay to me. Btw I tested with libudev as well,
> > its works well as we do send the event using kobject_uevent().
> 
> Where has it been used in other parts of the kernel like this?  Time to
> go yell at people :)
> 
> And the issue isn't that you will not catch the uevent, but that this is
> an attribute of the "parent" device, which is now not a device, but a
> "raw" kobject on no bus at all.
> 
> So, just create these as real struct devices, with a different "type"
> and have them all live on the bus properly.  Look at how the greybus
> code does it as one example (USB is another one, but it's much more
> complex.)

Thanks for the quick reply.

Are you sure greybus is a right example?

Looking at audio_manager.c we seem to create kset thus kobject without a
device. It lives off global sysfs!

Probing further I think you wanted to point me to gb_interface_create()
which I think would be similar to sdw_add_bus_master(). So we should
create a device without a driver for this and make kobjects live off it.

So IIUC it is okay to create kbojects but make sure we they live with a
'device' right?

Thanks
-- 
~Vinod