Hi Biju,
On Thu, 15 Jan 2026 at 11:10, Biju Das <[email protected]> wrote:
> > From: Geert Uytterhoeven <[email protected]>
> > On Thu, 15 Jan 2026 at 08:48, Biju Das <[email protected]> wrote:
> > > > From: Geert Uytterhoeven <[email protected]> On Wed, 3 Dec 2025
> > > > at 14:42, Tommaso Merciai <[email protected]> wrote:
> > > > > On Wed, Dec 03, 2025 at 09:23:53AM +0100, Krzysztof Kozlowski wrote:
> > > > > > On Wed, Nov 26, 2025 at 03:07:22PM +0100, Tommaso Merciai wrote:
> > > > > > > The RZ/G3E Soc has 2 LCD controller (LCDC), contain a Frame
> > > > > > > Compression Processor (FCPVD), a Video Signal Processor
> > > > > > > (VSPD), Video Signal Processor (VSPD), and Display Unit (DU).
> > > > > > >
> > > > > > > - LCDC0 supports DSI and LVDS (single or dual-channel) outputs.
> > > > > > > - LCDC1 supports DSI, LVDS (single-channel), and RGB outputs.
> > > > > > >
> > > > > > > Add then two new SoC-specific compatible strings
> > > > > > > 'renesas,r9a09g047-du0'
> > > > > > > and 'renesas,r9a09g047-du1'.
> > > > > >
> > > > > > LCDC0/1 but compatibles du0/du1...
> > > > > >
> > > > > > What are the differences between DU0 and DU1? Just different
> > > > > > outputs? Is the programming model the same?
> > > > >
> > > > > The hardware configurations are different: these are two distinct
> > > > > hardware blocks.
> > > > >
> > > > > Based on the block diagrams shown in Figures 9.4-2 (LCDC1) and
> > > > > 9.4-1 (LCDC0), the only difference concerns the output, but this
> > > > > variation is internal to the hardware blocks themselves.
> > > > > Therefore, LCDC0 and LCDC1 are not identical blocks, and their
> > > > > programming models differ as a result.
> > > > >
> > > > > In summary, although most of the internal functions are the same,
> > > > > the two blocks have output signals connected to different components
> > > > > within the SoC.
> > > > > This requires different hardware configurations and inevitably
> > > > > leads to different programming models for LCDC0 and LCDC1.
> > > >
> > > > Isn't that merely an SoC integration issue?
> > > > Are there any differences in programming LCDC0 or LCDC1 for the
> > > > common output types supported by both (single channel LVDS and 4-lane
> > > > MIPI-DSI)?
> > >
> > > Dual LVDS case, dot clock from LCDC0 is used in both LCDC's.
> >
> > For the single dual-channel LVDS output on LCDC0, or for using two
> > independent LVDS outputs on both
> > instances? How is this handled?
>
> Dual-channel LVDS output on LCDC0, we use the data from LCDC0.
That's the "dual-link" case below? But that case doesn't use LCDC1 at all,
so how can "dot clock from LCDC0 is used in both LCDC's" be true?
What am I missing?
>
> We have the following use cases:
>
> Single-link(ch0 only):
> This mode outputs the image data of LCDC0 to LVDS (ch0). In this mode,
> LVDS (ch1) is not used.
>
> Single-link(ch1 only):
> This mode outputs the image data of LCDC1 to LVDS (ch1).
> In this mode, LVDS (ch0) is not used.
>
> Single-link(2ch):
> In this mode, the image data of LCDC0 is output to LVDS (ch0) and the
> image data of LCDC1 is output to LVDS (ch1).
> Since LVDS (ch0) and LVDS (ch1) are not synchronously related, they
> can be output in different image formats and can be operated asynchronously.
>
> Single-link(Multi)
> In this mode, the image data of LCDC0 is output to both LVDS (ch0) and
> LVDS (ch1). LVDS (ch0) and LVDS (ch1) operate synchronously.
>
> Dual-link:
> In this mode, the input image data from LCDC0 is separated into Even pixels
> and
> Odd pixels, and the output is distributed to LVDS ch0 and ch1.
>
>
> > Don't you need a companion property to link them together?
>
> Yes, We use companion property for Dual channel LVDS(Dual-Link) use case.
> >
> > Is this similar to dual-channel LVDS on R-Car E3 and RZ/G2E?
>
> Yes.
OK, "companion" is in the renesas,lvds bindings, which are not yet updated
for RZ/G3E? Do you need it in "renesas,rzg2l-du", too?
> > On these SoCs we have a single combined device node for all DU instances
> > (which comes with its own set
> > of issues, e.g. Runtime PM and Clock Domain handling).
>
> But in our case, it has 2 separate independent LCDC IP's to allow all the
> possible outputs as mentioned above.
>
> > > Standalone LVDS and DSI the programming flow is same.
> >
> > OK.
> >
> > > > Of there are no such differences, both instances should use the same
> > > > compatible value.
> > >
> > > Then we need to use a property called display-id, to describe the
> > > supported output types in bindings, right??
> > >
> > > Display-id=0 {LVDS, DSI)
> >
> > LVDS twice?
>
> LCDC0 supports DSI and LVDS (single or dual-channel) outputs.
That's two ports for LVDS (i.e. "twice"), right?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
