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    SubjectRe: [alsa-devel] [RFC PATCH 1/7] soundwire: Add sysfs support for master(s)
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    On 5/8/19 4:16 AM, Greg KH wrote:
    > 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.

    Humm, confused...In the existing code bus and master are synonyms, see
    e.g. following code excerpts:

    * sdw_add_bus_master() - add a bus Master instance
    * @bus: bus instance
    *
    * Initializes the bus instance, read properties and create child
    * devices.

    struct sdw_bus {
    struct device *dev; <<< pointer here
    unsigned int link_id;
    struct list_head slaves;
    DECLARE_BITMAP(assigned, SDW_MAX_DEVICES);
    struct mutex bus_lock;
    struct mutex msg_lock;
    const struct sdw_master_ops *ops;
    const struct sdw_master_port_ops *port_ops;
    struct sdw_bus_params params;
    struct sdw_master_prop prop;

    The existing code creates a platform_device in
    drivers/soundwire/intel_init.c, and it's assigned by the following code:

    static int intel_probe(struct platform_device *pdev)
    {
    struct sdw_cdns_stream_config config;
    struct sdw_intel *sdw;
    int ret;

    sdw = devm_kzalloc(&pdev->dev, sizeof(*sdw), GFP_KERNEL);
    [snip]
    sdw->cdns.dev = &pdev->dev;
    sdw->cdns.bus.dev = &pdev->dev;

    I really don't see what you are hinting at, sorry, unless we are talking
    about major surgery in the code.

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