Re: [PATCH v2 1/2] media: dt-bindings: Add dt bindings for m2m-deinterlace device

[Matthew Majewski <mattwmajewski@gmail.com>]

Hi Krzysztof,

On Tue, 2025-02-18 at 09:30 +0100, Krzysztof Kozlowski wrote:
> On Fri, Feb 14, 2025 at 06:17:58PM -0500, Matthew Majewski wrote:
> > Create a new yaml schema file to describe the device tree bindings
> > for
> > generic m2m-deinterlace device.
> > 
> > This device is supported on any hardware that provides a MEM_TO_MEM
> 
> Which device? I don't see here any device name/model.

By "device" I am referring to the m2m-deinterlace device, which I
explained is a quasi-virtual device. If this is confusing wording I can
change. 

> I asked to provide here some examples of devices.

As I wrote, supported devices/hardware is anything that provides a
MEM_TO_MEM capable dma-controller with interleaved transfer support. I
did not list specific devices because the bindings are supposed to be
generic, as they are not describing actual silicon. But if you want me
to list some devices which provide a compatible dma-controller, here
are devices I found in the current mainline kernel:

- TI OMAP Soc Family
- TI Davinci Soc Family
- TI Keystone Processor Family
- IMX27 Processor and variants
- Several Microchip Processors (sama5, sam9x7, sam9x60)

As I mentioned in my original email, I have personally tested on a
BeagleBone Black with an AM335X OMAP processor. There are likely many
more devices with compatible dma-controllers that could be supported
with additional dmaengine driver support. 


> > capable dma channel with interleaved trasfer support. Device tree
> > bindings are for providing appropriate dma channel to device.
> 
> Don't describe what DT is, but the hardware.
> 

Ok, will remove reference to DT.

> > +description: |-
> > +  A generic memory2memory device for deinterlacing video using
> > dmaengine. It can
> > +  convert between interlaced buffer formats and can convert
> > interlaced to
> > +  progressive using a simple line-doubling algorithm. This device
> > can be used on
> > +  any hardware that provides a MEM_TO_MEM capable dma controller
> > that supports
> > +  interleaved transfers.
> 
> And how do you program that device to deinterlace? How do you signal
> end
> of frame/data when writing to the memory?
> 
> It still looks all this is for driver :/
> 

All of the deinterlacing is handled by the dma channel. To simplify a
bit, m2m-deinterlace basically just translates video format information
into appropriate interleaved dma transfers. Everything else (and
everything hardware specific) is handled by the dma engine, such as
initiation and signaling completion of transfers. 

I think an appropriate analogy for m2m-deinterlace would be spi-gpio.
Since spi-gpio leverages gpio for bitbanging the spi protocol, the
bindings do not need to describe any clocks, spi-controller registers,
etc. All of the hardware specific components are abstracted away by the
gpio controller. But the spi-gpio bindings still exist to specify which
gpios are used.

Best,
Matthew