linux-kernel - Re: [PATCH 5/5] soundwire: qcom: add sdw_master

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Date:   Fri, 20 Mar 2020 12:57:50 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        alsa-devel@...a-project.org
Cc:     tiwai@...e.de, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Hui Wang <hui.wang@...onical.com>, vkoul@...nel.org,
        broonie@...nel.org, Andy Gross <agross@...nel.org>,
        jank@...ence.com,
        "open list:ARM/QUALCOMM SUPPORT" <linux-arm-msm@...r.kernel.org>,
        slawomir.blauciak@...el.com, Sanyog Kale <sanyog.r.kale@...el.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>
Subject: Re: [PATCH 5/5] soundwire: qcom: add sdw_master_device support


>> Add new device as a child of the platform device, following the
>> following hierarchy:
>>
>> platform_device
>>      sdw_master_device
>>          sdw_slave0
> 
> Why can't we just remove the platform device layer here and add 
> sdw_master_device directly?
> 
> What is it stopping doing that?

The guidance from Greg was "no platform devices, unless you really are 
on a platform bus (i.e. Device tree.)". We never discussed changing the 
way the Device Tree parts are handled.

The main idea was to leave the parent (be it platform-device or PCI 
device) alone and not add new attributes or references to it.

The scheme here is similar to I2C/SPI, you have a platform device 
handled by the Device Tree baseline, and a driver create an 
i2c_adapter/spi_controller/sdw_master_device.