From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 67B2F1643B; Mon, 31 Aug 2026 05:54:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788155695; cv=none; b=PXs9YVIdTB6GVLssa9NKMQOSJBfynj8p2b0/31+PNjEhqp03dzlQ7QxzBkAAKvDd0ngrsD4aMESKAQk2hSTqUGY074rIRbkTGFcZporeFU+TGrzsW0TZlQCudBxSl0/oWorc4Chn1fbavoSPHXnbNgahkAJl7EkHT8EmJrAzSyI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788155695; c=relaxed/simple; bh=GVL2EDy/yfr3CnqyXlspatM2MKppPD8WpMK5sQoCsn0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=oVZE7hHWIbjwD2A0TD7IQ9to0BFR6wLJiET27/Y7uAktc9Uy3slobjxKvcjuUcW8plWVle56FVWDNDZrI4NyiNLsVY+G+vgH6yjXRnkPGw5F2AeyjD+HrxmxJgPOjFwrXGrge2l8koXjgodZgVNntfDf0fMd0BpNj6xxo7mgr6Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bIR8SRhZ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bIR8SRhZ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 249A71F000E9; Mon, 31 Aug 2026 05:54:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788155694; bh=vWXAI936j9ZzBxqqoX4RZz4P0wNKTqK49yAdRjOQ9/c=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=bIR8SRhZTNkdLtjj68xw0E6mq9aQV6CA27guS5+VG4RXMtMEewZJm0HreoUPURA2t Kd3/Tyn79nmXIp5P6SKDnggvPM5eIYZupgTmpwhXSejZoWhYyrDo6V/X1cyYLqyVYH OLwT+cdMbzEL6kqD/ZzSb8fAIG6NcPHZsuPeY4cBTKShhBc80dTfNPzuI0fyeTy9/X vRJ6/bKH+qVaRS9ZvhLHOVSXXqpn85SsdYU6RdvKGW4XtYc+5bwa1BvQlQLmu/06Hs 5ttHEdVsaeWJsoML7elfCqvPwkdhYID8eFHkw63ank75WeED0yK3y0ESAc5yK61EPE Cj80rlHBy3z3Q== Message-ID: <5f99fc90-02e0-40ab-8d1f-c2e7bcce7a5e@kernel.org> Date: Mon, 31 Aug 2026 07:54:48 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 2/2] soc: starfive: Add JHB100 UART Routing driver To: Changhuang Liang , Rob Herring , Krzysztof Kozlowski , Conor Dooley Cc: "linux-kernel@vger.kernel.org" , "devicetree@vger.kernel.org" References: <20260830065118.51551-1-changhuang.liang@starfivetech.com> <20260830065118.51551-3-changhuang.liang@starfivetech.com> <417251d0-c2cc-4e10-940d-b75ab20acdec@kernel.org> From: Krzysztof Kozlowski Content-Language: en-US Autocrypt: addr=krzk@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 31/08/2026 03:35, Changhuang Liang wrote: > Hi, Krzysztof > > Thanks for the review. > >> On 30/08/2026 08:51, Changhuang Liang wrote: >>> Add driver support for JHB100 UART Routing control, allowing runtime >>> configuration of RX muxes between UART controllers and I/O pins. >>> >>> A sysfs interface is provided for easy checking and updating of >>> routing paths. >>> >>> Signed-off-by: Changhuang Liang >>> --- >>> .../sysfs-driver-starfive-jhb100-uart-routing | 45 +++ >>> MAINTAINERS | 7 + >>> drivers/soc/starfive/Kconfig | 1 + >>> drivers/soc/starfive/Makefile | 1 + >>> drivers/soc/starfive/uart-routing/Kconfig | 14 + >>> drivers/soc/starfive/uart-routing/Makefile | 2 + >>> .../uart-routing/jhb100-uart-routing.c | 262 >> ++++++++++++++++++ >>> 7 files changed, 332 insertions(+) >>> create mode 100644 >>> Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-routing >>> create mode 100644 drivers/soc/starfive/uart-routing/Kconfig >>> create mode 100644 drivers/soc/starfive/uart-routing/Makefile >>> create mode 100644 >>> drivers/soc/starfive/uart-routing/jhb100-uart-routing.c >>> >>> diff --git >>> a/Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-routing >>> b/Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-routing >>> new file mode 100644 >>> index 000000000000..2844133bea1b >>> --- /dev/null >>> +++ b/Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-rout >>> +++ ing >>> @@ -0,0 +1,45 @@ >>> +What: >> /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*/uart\* >>> +Date: August 2026 >>> +Contact: Changhuang Liang >>> +Description: Selects the RX source of the UARTx device. >>> + >>> + When read, each file shows the list of available options with >> currently >>> + selected option marked by brackets "[]". The list of available options >>> + depends on the selected file. >>> + >>> + e.g. >>> + cat >> /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*.uart-routing/uart1 >>> + io0 [io1] io2 io3 io4 io5 io6 io7 io8 io9 io10 io11 io12 io13 io14 uart0 >> uart1 >>> + uart2 uart3 uart4 uart5 uart6 uart7 uart8 uart9 uart10 uart11 >>> +uart12 uart13 uart14 >>> + >>> + In this case, UART1 gets its input from IO1 (physical serial port 1). >>> + >>> + To switch the RX source of UART1 to UART2, write the desired >> source to the file: >>> + echo uart2 > >>> +/sys/bus/platform/drivers/starfive-jhb100-uart-routing/*.uart-routing >>> +/uart1 >>> + >>> + This indicates that UART1 now receives its input from UART2. >>> + >>> +Users: OpenBMC. Proposed changes should be mailed to >>> + openbmc@lists.ozlabs.org >>> + >>> +What: /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*/io\* >>> +Date: August 2026 >>> +Contact: Changhuang Liang >>> +Description: Selects the RX source of IOx serial port. The current >> selection >>> + will be marked by brackets "[]". The list of available options >>> + depends on the selected file. >>> + >>> + e.g. >>> + cat >> /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*.uart-routing/io9 >>> + uart0 uart1 uart2 uart3 uart4 uart5 uart6 uart7 uart8 [uart9] uart10 >> uart11 uart12 >>> + uart13 uart14 io0 io1 io2 io3 io4 io5 io6 io7 io8 io9 io10 io11 >>> +io12 io13 io14 >>> + >>> + In this case, IO9 (physical serial port 9) gets its input from UART9. >>> + >>> + To switch the RX source of IO9 to UART10, write the desired source >> to the file: >>> + echo uart10 > >>> +/sys/bus/platform/drivers/starfive-jhb100-uart-routing/*.uart-routing >>> +/io9 >>> + >>> + This indicates that IO9 now receives its input from UART10. >>> + >>> +Users: OpenBMC. Proposed changes should be mailed to >>> + openbmc@lists.ozlabs.org >> >> drivers/soc/ should not define user-space interfaces. This is not the place for >> them. You need to route user-spaces interfaces only through one of other >> approved subsystems, after their review. >> >> This looks like pin multiplexing interface. > > I may have misunderstood somethingļ¼Œplease correct me if I'm wrong: > > I have found two subsystems related to multiplexing so far: > > /drivers/pinctrl and /drivers/mux. However, neither of them seems to provide a > user-space interface for switching multiplexing values. > > Do you have any suggestions on this? pinctrl has some interface, not sure if writable, though. If interface is missing, it should be added via such subsystem. > > Also, could you confirm whether the implementation in drivers/soc/aspeed/aspeed-uart-routing.c > is there for historical reasons? I supposed sneaked in without SoC maintainers noticing. > > Best Regards, > Changhuang Best regards, Krzysztof