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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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