linux-kernel - Re: [PATCH v4] riscv: dts: spacemit: add UART pinctrl combinations

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Message-ID: <b76520ff-f039-465c-a58d-8f0f37bd1664@hammernet.be>
Date: Wed, 17 Sep 2025 10:17:16 +0200
From: Hendrik Hamerlinck <hendrik.hamerlinck@...mernet.be>
To: Troy Mitchell <troy.mitchell@...ux.spacemit.com>, dlan@...too.org
Cc: paul.walmsley@...ive.com, palmer@...belt.com, alex@...ti.fr,
 aou@...s.berkeley.edu, conor+dt@...nel.org, krzk+dt@...nel.org,
 robh@...nel.org, skhan@...uxfoundation.org,
 linux-kernel-mentees@...ts.linux.dev, devicetree@...r.kernel.org,
 linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] riscv: dts: spacemit: add UART pinctrl combinations

Hello Troy,

Thank you for reviewing.

On 9/17/25 09:46, Troy Mitchell wrote:
> Hi Hendrik, Thanks for your patch!
>
> On Wed, Sep 17, 2025 at 08:59:07AM +0200, Hendrik Hamerlinck wrote:
>> Add UART pinctrl configurations based on the SoC datasheet and the
>> downstream Bianbu Linux tree. The drive strength values were taken from
>> the downstream implementation, which uses medium drive strength.
>> CTS/RTS are moved to separate *-cts-rts-cfg states so boards can enable
>> hardware flow control conditionally.
>>
>> Signed-off-by: Hendrik Hamerlinck <hendrik.hamerlinck@...mernet.be>
>> Reviewed-by: Yixun Lan <dlan@...too.org>
>> ---
>> Changes in v4:
>> - Explicitly use 0 as bias-pull-up value
>>
>> Changes in v3:
>> - Added /omit-if-no-ref/ to pinctrl states to reduce DT size
>>
>> Changes in v2:
>> - Split cts/rts into separate pinctrl configs as suggested
>> - Removed options from board DTS files to keep them cleaner
>> ---
>>  arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi | 430 ++++++++++++++++++-
>>  1 file changed, 428 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi b/arch/riscv/boot/dts/spacemit/k1-pinctrl.dtsi
>> +	/omit-if-no-ref/
>> +	uart2_0_cts_rts_cfg: uart2-0-cts-rts-cfg {
>> +		uart2-0-pins {
>> +			pinmux = <K1_PADCONF(23, 1)>,	/* uart2_cts */
>> +				 <K1_PADCONF(24, 1)>;	/* uart2_rts */
>> +			bias-pull-up = <0>;
>> +			drive-strength = <32>;
>> +		};
>> +	};
> We are currently using the 8250 UART driver, but hardware flow control does not
> work properly on K1. We are considering fixing this when time permits.
>
> Should we add a comment here to avoid confusing others who may run into this?
> If so, I will remove the comment once the issue has been fixed.
Not sure if I’m missing something, but hardware flow control seems to work
with the `8250_of` driver?

On both ends I configured the ports with:
`stty -F /dev/ttyS1 115200 crtscts -ixon -ixoff raw -echo`

With this setup, data sent with echo only goes through when the peer is
actually reading on the other side, which looks like RTS/CTS is
functioning correctly.

>
> Anyway,
>
> Reviewed-by: Troy Mitchell <troy.mitchell@...ux.spacemit.com>
>> +
>> +	/omit-if-no-ref/
>> +	uart3_0_cfg: uart3-0-cfg {
>> +		uart3-0-pins {
>> +			pinmux = <K1_PADCONF(81, 2)>,	/* uart3_txd */
>> +				 <K1_PADCONF(82, 2)>;	/* uart3_rxd */
>> +			bias-pull-up = <0>;
>> +			drive-strength = <32>;
>> +		};
>> +	};
>> +
...
>> -- 
>> 2.43.0
>>
>>
>> _______________________________________________
>> linux-riscv mailing list
>> linux-riscv@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-riscv
Kind regards,
Hendrik

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