linux-kernel - Re: [RFC 1/5] soundwire: bus_type: add sdw_master

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Date:   Tue, 28 Apr 2020 13:21:45 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Bard Liao <yung-chuan.liao@...ux.intel.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, jank@...ence.com,
        srinivas.kandagatla@...aro.org, rander.wang@...ux.intel.com,
        ranjani.sridharan@...ux.intel.com, hui.wang@...onical.com,
        pierre-louis.bossart@...ux.intel.com, sanyog.r.kale@...el.com,
        slawomir.blauciak@...el.com, mengdong.lin@...el.com
Subject: Re: [RFC 1/5] soundwire: bus_type: add sdw_master_device support

On 28-04-20, 08:55, Greg KH wrote:
> On Tue, Apr 28, 2020 at 12:19:51PM +0530, Vinod Koul wrote:
> > On 28-04-20, 08:37, Greg KH wrote:
> > > On Tue, Apr 28, 2020 at 10:01:44AM +0530, Vinod Koul wrote:
> > > > > > That is not true for everyone, it is only true for Intel, pls call that
> > > > > > out as well...
> > > > > 
> > > > > Why is it not true for everyone?  How else do you get the pm stuff back
> > > > > to your hardware?
> > > > 
> > > > The rest of the world would do using the real controller device. For
> > > > example the soundwire controller on Qualcomm devices is enumerated as a
> > > > DT device and is using these...
> > > > 
> > > > If Intel had a standalone controller or enumerated as individual
> > > > functions, it would have been a PCI device and would manage as such
> > > 
> > > If it is not a standalone controller, what exactly is it?  I thought it
> > > was an acpi device, am I mistaken?
> > > 
> > > What is the device that the proper soundwire controller driver binds to
> > > on an Intel-based system?
> > 
> > The HDA controller which is a PCI device. The device represent HDA
> > function, DSP and Soundwire controller instances (yes it is typically
> > more than one instance)
> 
> Then those "instances" should be split up into individual devices that a
> driver can bind to.  See the work happening on the "virtual" bus for
> examples of how that can be done.

Yes removing platform devices is the goal for Intel now :) Pierre & Bard
have been diligently trying to solve this.

Only difference is the means to end goal. I am not convinced that this
should be in soundwire subsystem.

Looks like folks are trying to review and port to use this bus. Makes
sense to me..
https://lore.kernel.org/netdev/c5197d2f-3840-d304-6b09-d334cae81294@linux.intel.com/

> A platform device better not be being used here, I'm afraid to look at
> the code now...

Well if the plan for 'virtual-bus' goes well, it should be  a simple
replacement of platform->virtual for Intel driver. Rest of the driver
should not be impacted :)

Thanks
-- 
~Vinod