Re: [PATCH v4 3/3] LoongArch: dts: Add uart new compatible string

[Krzysztof Kozlowski <krzk@kernel.org>]

On 11/09/2025 09:55, Binbin Zhou wrote:
> Hi Krzysztof:
> 
> Thanks for your reply.
> 
> On Wed, Sep 10, 2025 at 4:27 PM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>>
>> On Tue, Sep 09, 2025 at 08:11:20PM +0800, Binbin Zhou wrote:
>>> Add loongson,ls2k*-uart compatible string on uarts.
>>>
>>> Co-developed-by: Haowei Zheng <zhenghaowei@loongson.cn>
>>> Signed-off-by: Haowei Zheng <zhenghaowei@loongson.cn>
>>> Signed-off-by: Binbin Zhou <zhoubinbin@loongson.cn>
>>> ---
>>>  arch/loongarch/boot/dts/loongson-2k0500.dtsi | 2 +-
>>>  arch/loongarch/boot/dts/loongson-2k1000.dtsi | 2 +-
>>>  arch/loongarch/boot/dts/loongson-2k2000.dtsi | 2 +-
>>>  3 files changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/loongarch/boot/dts/loongson-2k0500.dtsi b/arch/loongarch/boot/dts/loongson-2k0500.dtsi
>>> index 588ebc3bded4..357de4ca7555 100644
>>> --- a/arch/loongarch/boot/dts/loongson-2k0500.dtsi
>>> +++ b/arch/loongarch/boot/dts/loongson-2k0500.dtsi
>>> @@ -380,7 +380,7 @@ tsensor: thermal-sensor@1fe11500 {
>>>               };
>>>
>>>               uart0: serial@1ff40800 {
>>> -                     compatible = "ns16550a";
>>> +                     compatible = "loongson,ls2k0500-uart", "ns16550a";
>>
>> You clearly never bothered to actually test this against own code.
> 
> Sorry, perhaps I should have included more detailed descriptions in
> the binding file.
> 
> As per Chapter 15 of the Loongson-3A5000 manual[1], the Loongson UART
> registers and functionality are compatible with the NS16550A. However,
> generic 16550A drivers cannot support full serial port capabilities,
> such as hardware flow control.
> 
> Based on your feedback in the V3 patchset[2], I attempted to use
> compatible fallbacks to avoid API breakage.
> 
> These fallbacks match according to the Makefile's compilation

DT bindings and fallbacks in DTS cannot match Makefile. You are mixing
concepts.

I said, this was not tested. I am 100% sure. Instead of replying with
irrelevant build related stuff, please come with actual arguments, e.g.
output (on some pastebin.com) of entire dtbs_check proving no new
warnings are there.

But even without warnings, I see with my own eyes that DTS is just
wrong. Or bindings.

Best regards,
Krzysztof