linux-kernel - Re: [RFC PATCH 1/2] dt-bindings: tas2562: Add firmware support for tas2563

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Date:   Wed, 17 Jun 2020 16:04:59 -0600
From:   Rob Herring <robh@...nel.org>
To:     Dan Murphy <dmurphy@...com>
Cc:     Mark Brown <broonie@...nel.org>, lgirdwood@...il.com,
        perex@...ex.cz, tiwai@...e.com, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] dt-bindings: tas2562: Add firmware support for
 tas2563

On Wed, Jun 10, 2020 at 09:12:15AM -0500, Dan Murphy wrote:
> Mark
> 
> On 6/10/20 5:29 AM, Mark Brown wrote:
> > On Tue, Jun 09, 2020 at 02:20:29PM -0500, Dan Murphy wrote:
> > > On 6/9/20 1:47 PM, Mark Brown wrote:
> > > > That's really not very idiomatic for how Linux does stuff and seems to
> > > > pretty much guarantee issues with hotplugging controls and ordering -
> > > > you'd need special userspace to start up even if it was just a really
> > > > simple DSP config doing only speaker correction or something.  I'm not
> > > > sure what the advantage would be - what problem is this solving over
> > > > static names?
> > > IMO having a static name is the problem. It is an inflexible design.
> > > Besides the firmware-name property seems to be used in other drivers to
> > > declare firmwares for the boards.
> > > But if no one is complaining or submitting patches within the codecs to be
> > > more flexible with firmware then I can just hard code the name like other
> > > drivers do.
> > I'm not *completely* opposed to having the ability to suggest a name in
> > firmware, the big problem is making use of the DSP completely dependent
> > on having a DT property or doing some non-standard dance in userspace.
> 
> Well from what I see we have 4 options.
> 
> 1.  We can have a DT node like RFC'd (Need Rob's comments here)

We've obviously already allowed 'firmware-name', but the preference is 
still not putting into DT. It's really a Linux userspace interface.

> 2.  We can have a defconfig flag that hard codes the name (This will
> probably be met with some resistance if not some really bad reactions and I
> don't prefer to do it this way)
> 
> 3.  We can hard code the name of the firmware in the c file.
> 
> 4.  Dynamically derive a file name based on the I2C bus-address-device so it
> would be expected to be "2_4c_tas2563.bin".  Just need to figure out how to
> get the bus number.

Given bus numbering may not be constant, that seems like not the best 
way to match up devices. I'd assume that userspace needs some way to 
identify which instance is which already, so maybe there's other data 
you can use already.

> I don't see the user space as a viable option because the codec will have to
> load and then the user space would have to request to load the firmware and
> then more mixer controls will appear.
> 
> Again only option 1 allows us to have different firmware binaries per IC
> instance and also denotes the use of the DSP.  The DSP is not programmed
> until the user space selects the program or configuration from the binary. 
> So special audio handling is very explicit in the user space.  More then
> likely most standard distributions will not even use the DSP for this device
> it is more of a specialized use case for each product.
> 
> 
>