[PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[Frank Li]

i.MX6SX uses the v6 LCDIF controller, while i.MX28 uses the older v4
version. The driver has supported the "fsl,imx6sx-lcdif" compatible string
since the initial commit:

   commit 45d59d704080 ("drm: Add new driver for MXSFB controller")

Therefore the fallback compatible string "fsl,imx28-lcdif" is not required
and can be removed.

Fix the following CHECK_DTB warning:
/arch/arm/boot/dts/nxp/imx/imx6sx-nitrogen6sx.dtb: lcdif@2220000 (fsl,imx6sx-lcdif): compatible: 'oneOf' conditional failed, one must be fixed:
        ['fsl,imx6sx-lcdif', 'fsl,imx28-lcdif'] is too long

Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
Cc: Liu Ying <victor.liu@nxp.com>
Cc: Fabio Estevam <festevam@gmail.com>
Previous Fabio Estevam work try to allow fallback at
https://lore.kernel.org/imx/42eb2d42-47b0-46b6-92e9-c59473113c2d@nxp.com/
---
 arch/arm/boot/dts/nxp/imx/imx6sx.dtsi | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi b/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi
index 1426f357d4744..aefae5a3a6beb 100644
--- a/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi
+++ b/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi
@@ -1304,7 +1304,7 @@ csi2: csi@221c000 {
 				};
 
 				lcdif1: lcdif@2220000 {
-					compatible = "fsl,imx6sx-lcdif", "fsl,imx28-lcdif";
+					compatible = "fsl,imx6sx-lcdif";
 					reg = <0x02220000 0x4000>;
 					interrupts = <GIC_SPI 5 IRQ_TYPE_EDGE_RISING>;
 					clocks = <&clks IMX6SX_CLK_LCDIF1_PIX>,
@@ -1325,7 +1325,7 @@ lcdif1_to_ldb: endpoint {
 				};
 
 				lcdif2: lcdif@2224000 {
-					compatible = "fsl,imx6sx-lcdif", "fsl,imx28-lcdif";
+					compatible = "fsl,imx6sx-lcdif";
 					reg = <0x02224000 0x4000>;
 					interrupts = <GIC_SPI 6 IRQ_TYPE_EDGE_RISING>;
 					clocks = <&clks IMX6SX_CLK_LCDIF2_PIX>,
-- 
2.43.0

Re: [PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[Krzysztof Kozlowski]

On 05/03/2026 22:23, Frank Li wrote:
> i.MX6SX uses the v6 LCDIF controller, while i.MX28 uses the older v4
> version. The driver has supported the "fsl,imx6sx-lcdif" compatible string
> since the initial commit:
> 
>    commit 45d59d704080 ("drm: Add new driver for MXSFB controller")
> 
> Therefore the fallback compatible string "fsl,imx28-lcdif" is not required
> and can be removed.

It is required - you are changing the ABI and possibly impacting other
users without valid reason ("not required and can be removed" is not a
reason).

Best regards,
Krzysztof

Re: [PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[Frank Li]

On Thu, Mar 05, 2026 at 10:34:18PM +0100, Krzysztof Kozlowski wrote:
> On 05/03/2026 22:23, Frank Li wrote:
> > i.MX6SX uses the v6 LCDIF controller, while i.MX28 uses the older v4
> > version. The driver has supported the "fsl,imx6sx-lcdif" compatible string
> > since the initial commit:
> >
> >    commit 45d59d704080 ("drm: Add new driver for MXSFB controller")
> >
> > Therefore the fallback compatible string "fsl,imx28-lcdif" is not required
> > and can be removed.
>
> It is required - you are changing the ABI and possibly impacting other
> users without valid reason ("not required and can be removed" is not a
> reason).

In https://lore.kernel.org/imx/42eb2d42-47b0-46b6-92e9-c59473113c2d@nxp.com/

other known user barebox/uboot already fix it.

https://lore.barebox.org/barebox/20251107210033.2229781-3-a.fatoum@barebox.org/T/#u
https://git.pengutronix.de/cgit/barebox/commit/?id=c99b937f3a31

Frank

>
> Best regards,
> Krzysztof

Re: [PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[Liu Ying]

On Thu, Mar 05, 2026 at 10:34:18PM +0100, Krzysztof Kozlowski wrote:
> On 05/03/2026 22:23, Frank Li wrote:
>> i.MX6SX uses the v6 LCDIF controller, while i.MX28 uses the older v4
>> version. The driver has supported the "fsl,imx6sx-lcdif" compatible string
>> since the initial commit:
>>
>>    commit 45d59d704080 ("drm: Add new driver for MXSFB controller")
>>
>> Therefore the fallback compatible string "fsl,imx28-lcdif" is not required
>> and can be removed.
> 
> It is required - you are changing the ABI and possibly impacting other
> users without valid reason ("not required and can be removed" is not a
> reason).

People may argue that both DT binding schemas and DT nodes are ABIs.
The problem here is that fsl,lcdif.yaml contradicts with the
"lcdif@2220000" and "lcdif@2224000" DT nodes.

The only way not to break the ABIs is to additionally allow the i.MX28
LCDIF fallback for i.MX6SX LCDIF by changing fsl,lcdif.yaml like below.
But, it looks like a bit weird to allow both "fsl,imx6sx-lcdif" and
"fsl,imx6sx-lcdif, fsl,imx28-lcdif", and I still don't think i.MX28
LCDIF is a fallback for i.MX6SX LCDIF from hardware IP point of view.

--- a/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
+++ b/Documentation/devicetree/bindings/display/fsl,lcdif.yaml
@@ -32,6 +32,9 @@ properties:
               - fsl,imx8mn-lcdif
               - fsl,imx8mq-lcdif
           - const: fsl,imx6sx-lcdif
+      - items:
+          - const: fsl,imx6sx-lcdif
+          - const: fsl,imx28-lcdif
 
   reg:
     maxItems: 1

Considering that Barebox added fsl,imx6sx-lcdif compatible string in display
driver by commit[1] and Uboot has already supported the compatible string
in it's display driver, this patch has kind of low risk to break the ABI,
though in thoery some other unknown projects might be broken(but, I believe
those projects should be fixed just like Barebox did with commit[1]).

[1] https://github.com/barebox/barebox/commit/2ddbc8d9d15c8db23225785b6b8ebc3cb309e435

> 
> Best regards,
> Krzysztof

-- 
Regards,
Liu Ying

Re: [PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[Liu Ying]

On Thu, Mar 05, 2026 at 04:23:11PM -0500, Frank Li wrote:
> i.MX6SX uses the v6 LCDIF controller, while i.MX28 uses the older v4

V6 is a Linux thing as mxsfb_drv.c says:
/*
 * Starting at i.MX6 the hardware version register is gone, use the
 * i.MX family number as the version.
 */
MXSFB_V6,

I think it would be good to make the commit mesg independent from Linux.
You may say something like "i.MX6SX LCDIF is not compatible with
i.MX28 LCDIF from HW IP point of view like missing a/b/c registers".

> version. The driver has supported the "fsl,imx6sx-lcdif" compatible string
> since the initial commit:
> 
>    commit 45d59d704080 ("drm: Add new driver for MXSFB controller")
> 
> Therefore the fallback compatible string "fsl,imx28-lcdif" is not required
> and can be removed.
> 
> Fix the following CHECK_DTB warning:
> /arch/arm/boot/dts/nxp/imx/imx6sx-nitrogen6sx.dtb: lcdif@2220000 (fsl,imx6sx-lcdif): compatible: 'oneOf' conditional failed, one must be fixed:
>         ['fsl,imx6sx-lcdif', 'fsl,imx28-lcdif'] is too long
> 
> Signed-off-by: Frank Li <Frank.Li@nxp.com>

Since this is a fix, worth a Fixes tag?

> ---
> Cc: Liu Ying <victor.liu@nxp.com>
> Cc: Fabio Estevam <festevam@gmail.com>
> Previous Fabio Estevam work try to allow fallback at
> https://lore.kernel.org/imx/42eb2d42-47b0-46b6-92e9-c59473113c2d@nxp.com/
> ---
>  arch/arm/boot/dts/nxp/imx/imx6sx.dtsi | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi b/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi
> index 1426f357d4744..aefae5a3a6beb 100644
> --- a/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi
> +++ b/arch/arm/boot/dts/nxp/imx/imx6sx.dtsi
> @@ -1304,7 +1304,7 @@ csi2: csi@221c000 {
>  				};
>  
>  				lcdif1: lcdif@2220000 {
> -					compatible = "fsl,imx6sx-lcdif", "fsl,imx28-lcdif";
> +					compatible = "fsl,imx6sx-lcdif";
>  					reg = <0x02220000 0x4000>;
>  					interrupts = <GIC_SPI 5 IRQ_TYPE_EDGE_RISING>;
>  					clocks = <&clks IMX6SX_CLK_LCDIF1_PIX>,
> @@ -1325,7 +1325,7 @@ lcdif1_to_ldb: endpoint {
>  				};
>  
>  				lcdif2: lcdif@2224000 {
> -					compatible = "fsl,imx6sx-lcdif", "fsl,imx28-lcdif";
> +					compatible = "fsl,imx6sx-lcdif";
>  					reg = <0x02224000 0x4000>;
>  					interrupts = <GIC_SPI 6 IRQ_TYPE_EDGE_RISING>;
>  					clocks = <&clks IMX6SX_CLK_LCDIF2_PIX>,

-- 
Regards,
Liu Ying

Re: [PATCH 1/1] ARM: dts: imx6sx: remove fallback compatible string fsl,imx28-lcdif

[Krzysztof Kozlowski]

On 05/03/2026 23:48, Frank Li wrote:
> On Thu, Mar 05, 2026 at 10:34:18PM +0100, Krzysztof Kozlowski wrote:
>> On 05/03/2026 22:23, Frank Li wrote:
>>> i.MX6SX uses the v6 LCDIF controller, while i.MX28 uses the older v4
>>> version. The driver has supported the "fsl,imx6sx-lcdif" compatible string
>>> since the initial commit:
>>>
>>>    commit 45d59d704080 ("drm: Add new driver for MXSFB controller")
>>>
>>> Therefore the fallback compatible string "fsl,imx28-lcdif" is not required
>>> and can be removed.
>>
>> It is required - you are changing the ABI and possibly impacting other
>> users without valid reason ("not required and can be removed" is not a
>> reason).
> 
> In https://lore.kernel.org/imx/42eb2d42-47b0-46b6-92e9-c59473113c2d@nxp.com/
> 
> other known user barebox/uboot already fix it.
> 
> https://lore.barebox.org/barebox/20251107210033.2229781-3-a.fatoum@barebox.org/T/#u
> https://git.pengutronix.de/cgit/barebox/commit/?id=c99b937f3a31

And you have entire commit msg to explain the ABI impact...

Best regards,
Krzysztof