linux-kernel - Re: [PATCH] riscv: dts: spacemit: add UART resets for Soc K1

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Message-ID: <1a4a25d2-25a1-4d06-bba6-50f51cfbb619@hammernet.be>
Date: Wed, 20 Aug 2025 20:27:53 +0200
From: Hendrik Hamerlinck <hendrik.hamerlinck@...mernet.be>
To: dlan@...too.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, paul.walmsley@...ive.com, palmer@...belt.com,
 aou@...s.berkeley.edu, alex@...ti.fr
Cc: 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, elder@...cstar.com
Subject: Re: [PATCH] riscv: dts: spacemit: add UART resets for Soc K1

Hello,

On 8/7/25 21:18, Hendrik Hamerlinck wrote:
> Add reset control entries for all UARTs in the SpaceMIT K1 SoC Device Tree.
> UART0 was functional as it did not need a reset. But the other UARTs were
> unable to access their registers without the reset being applied.
>
> Although perhaps not needed I did add the reset for UART0 as well,
> to ensure consistency across all UARTs. With the current-speed set to
> 112500 baud rate, it matches the factory U-Boot settings.
> This should not give issues with early console usage. But perhaps it could
> be a good idea to let somebody else confirm this as well.
I have tested this version for a while and no longer see the need for
additional confirmation.

>
> Tested this locally on both Orange Pi RV2 and Banana Pi BPI-F3 boards. 
> I enabled the UART9 and was able to use it successfully.
>
Just a gentle reminder about this patch.

All UARTs are listed in the K1 device tree and probed by the 8250_of driver,
but without reset lines most of them are non-functional. Adding the resets
makes them usable when mapped to devices.

This patch is limited to DTS reset handling, so UARTs are usable in the
current state. I’m aware Alex Elder is assigned to the UART peripheral on
the wiki and will likely handle the broader driver improvements (DMA,
clock updates, full baud-rate support), so this should not interfere with
that work.

Thanks for taking a look!

Kind regards,
Hendrik