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