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

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Date:   Wed, 8 May 2019 11:16:28 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        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 Wed, May 08, 2019 at 01:16:06PM +0530, Vinod Koul wrote:
> On 07-05-19, 17:49, Pierre-Louis Bossart wrote:
> > 
> > > > 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.
> > 
> > humm, you lost me on the last sentence. Did you mean using
> > set_drv/platform_data during the init and retrieving the bus information
> > with get_drv/platform_data as needed later? Or something else I badly need
> > to learn?
> 
> IIUC Greg meant we should represent a soundwire master device type and
> use that here. Just like we have soundwire slave device type. Something
> like:
> 
> struct sdw_master {
>         struct device dev;
>         struct sdw_master_prop *prop;
>         ...
> };
> 
> In show function you get master from dev (container of) and then use
> that to access the master properties. So int.sdw.0 can be of this type.

Yes, you need to represent the master device type if you are going to be
having an internal representation of it.

thanks,

greg k-h