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 13:16:06 +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 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.

Thanks
-- 
~Vinod