[PATCH v2] drm/bridge: fsl-ldb: Parse register offsets from DT

[Marek Vasut]

On 11/3/25 4:55 PM, Luca Ceresoli wrote:

Hello Luca,

> On Sun Nov 2, 2025 at 6:02 PM CET, Marek Vasut wrote:
>> The DT binding for this bridge describe register offsets for the LDB,
>> parse the register offsets from DT instead of hard-coding them in the
>> driver. No functional change.
>>
>> Signed-off-by: Marek Vasut <marek.vasut at mailbox.org>
> 
> I was initially a bit skeptical because normally register offsets are
> derived from the compatible string, not from device tree. But then I
> realized this is about the LDB which has its two registers in the
> MEDIA_BLK. This means all in all this looks somewhat like an integration
> aspect (the LDB component uses two resources of the MEDIA_CLK component)
> and your patch mekse sense.
> 
> So my only remark is that the above may be in the commit message, to make
> the "why" clear from the beginning. It took a bit of research for me to
> find out.

Actually, the LDB was always meant to parse the 'reg' offsets out of the 
DT, it then went somewhat ... wrong ... and we ended up with hard-coded 
reg<->compatible mapping. It was never intended to be that way. That is 
all there is to it, there isn't any deeper reason behind it.

What would you add into the commit message ?

> Laurentiu's patch adding i.MX94 support will conflict with this
> one. Whichever gets applied after the other will have to be adapted
> accordingly.

It would be good to clean this driver up before we add more functionality.

> [0] https://lore.kernel.org/dri-devel/20251103-dcif-upstreaming-v6-3-76fcecfda919@oss.nxp.com/
> 
>> @@ -309,6 +302,27 @@ static int fsl_ldb_probe(struct platform_device *pdev)
>>   	fsl_ldb->dev = &pdev->dev;
>>   	fsl_ldb->bridge.of_node = dev->of_node;
>>
>> +	/* No "reg-names" property likely means single-register LDB */
> 
> Uh? If it is "likely" it means we are not sure this code is not introducing
> regressions, and that would be bad.

I can drop the 'likely' part.

>> +	idx = of_property_match_string(dev->of_node, "reg-names", "ldb");
>> +	if (idx < 0) {
>> +		fsl_ldb->single_ctrl_reg = true;
>> +		idx = 0;
>> +	}
> 
>  From the bindings I understand that having two 'reg' values and no
> 'reg-names' at all is legal. Your patch implies differently. Who's right
> here?
I think if you have two two reg values, you should have reg-names , so 
the binding should be updated ?