linux-kernel - Re: [alsa-devel] [RFC PATCH 2/7] soundwire: add Slave sysfs support

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Message-ID: <20190507051959.GC16052@vkoul-mobl>
Date:   Tue, 7 May 2019 10:49:59 +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 2/7] soundwire: add Slave sysfs support

On 06-05-19, 11:46, Pierre-Louis Bossart wrote:
> On 5/6/19 11:22 AM, Vinod Koul wrote:
> > On 06-05-19, 17:19, Greg KH wrote:
> > > On Mon, May 06, 2019 at 09:42:35AM -0500, Pierre-Louis Bossart wrote:
> > > > > > +
> > > > > > +int sdw_sysfs_slave_init(struct sdw_slave *slave)
> > > > > > +{
> > > > > > +	struct sdw_slave_sysfs *sysfs;
> > > > > > +	unsigned int src_dpns, sink_dpns, i, j;
> > > > > > +	int err;
> > > > > > +
> > > > > > +	if (slave->sysfs) {
> > > > > > +		dev_err(&slave->dev, "SDW Slave sysfs is already initialized\n");
> > > > > > +		err = -EIO;
> > > > > > +		goto err_ret;
> > > > > > +	}
> > > > > > +
> > > > > > +	sysfs = kzalloc(sizeof(*sysfs), GFP_KERNEL);
> > > > > 
> > > > > Same question as patch 1, why a new device?
> > > > 
> > > > yes it's the same open. In this case, the slave devices are defined at a
> > > > different level so it's also confusing to create a device to represent the
> > > > slave properties. The code works but I am not sure the initial directions
> > > > are correct.
> > > 
> > > You can just make a subdir for your attributes by using the attribute
> > > group name, if a subdirectory is needed just to keep things a bit more
> > > organized.
> > 
> > The key here is 'a subdir' which is not the case here. We did discuss
> > this in the initial patches for SoundWire which had sysfs :)
> > 
> > The way MIPI disco spec organized properties, we have dp0 and dpN
> > properties each of them requires to have a subdir of their own and that
> > was the reason why I coded it to be creating a device.
> 
> Vinod, the question was not for dp0 and dpN, it's fine to have
> subdirectories there, but rather why we need separate devices for the master
> and slave properties.

Slave does not have a separate device. IIRC the properties for Slave are
in /sys/bus/soundwire/device/<slave>/...

For master yes we can skip the device creation, it was done for
consistency sake of having these properties ties into sys/bus/soundwire/

I don't mind if they are shown up in respective device node (PCI/platform
etc) /sys/bus/foo/device/<> 

But for creating subdirectories you would need the new dpX devices.

HTH

> 
> > 
> > Do we have a better way to handle this?
> > 
> > > Otherwise, you need to mess with having multiple "types" of struct
> > > device all associated with the same bus.  It is possible, and not that
> > > hard, but I don't think you are doing that here.
> > > 
> > > thnaks,
> > > 
> > > greg k-h
> > 

-- 
~Vinod