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

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Date:   Thu, 30 Apr 2020 10:27:01 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Bard liao <yung-chuan.liao@...ux.intel.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        pierre-louis.bossart@...ux.intel.com, alsa-devel@...a-project.org,
        tiwai@...e.de, mengdong.lin@...el.com,
        linux-kernel@...r.kernel.org, ranjani.sridharan@...ux.intel.com,
        hui.wang@...onical.com, broonie@...nel.org,
        srinivas.kandagatla@...aro.org, jank@...ence.com,
        slawomir.blauciak@...el.com, sanyog.r.kale@...el.com,
        rander.wang@...ux.intel.com
Subject: Re: [RFC 1/5] soundwire: bus_type: add sdw_master_device support

On 30-04-20, 11:24, Bard liao wrote:
> 
> On 4/28/2020 3:51 PM, Vinod Koul wrote:
> > 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 :)
> 
> We can't expect when will 'virtual-bus' be upstream and it's not feasible
> to wait forever. Can we move forward with current solution and switch to
> 'virtual-bus' whenever it is upstream?

the move from platform-device to virtual-device should happen once
the virtual-bus' is accepted upstream. till then imo you should continue
with current platform device and once you have virtual-bus upstream,
replace it with virtual-device. Note: I am going to hold you on that :)

Rest of the pieces like sdw_master_device and sysfs parts are not
dependent upon this and should be sent for review and we can merge when
ready, hopefully for 5.8.

Thanks
-- 
~Vinod