From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 65FD8C61DC2 for ; Mon, 24 Aug 2026 12:53:45 +0000 (UTC) Received: from mail-lf1-f54.google.com (mail-lf1-f54.google.com [209.85.167.54]) by mx.groups.io with SMTP id smtpd.msgproc02-g2.3454.1787302329159273721 for ; Fri, 21 Aug 2026 01:52:09 -0700 Authentication-Results: mx.groups.io; dkim=none (message not signed); spf=pass (domain: gmail.com, ip: 209.85.167.54, mailfrom: tanurelinux@gmail.com) Received: by mail-lf1-f54.google.com with SMTP id 2adb3069b0e04-5b29599b81cso916901e87.1 for ; Fri, 21 Aug 2026 01:52:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1787302327; x=1787907127; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to:content-type; bh=HrPgnIHeq4cFyK/AEvCe99MeH0e/iWUMnbxmzeRgrQg=; b=hMKB7kypsNRTVHAc6MDuNrag4rqS2MfBmVCSbitJCXtXZr5cJDS6u+1ICRPvzwfNK2 AC4dj2+4MeiEYpDkliw9T9BS4B/c7w/RVmsb9zKHv8OSPLOb5iKz4xL/HDA25NtsdFoI 8HaR9bHuoYW8WGZ7BjFk7WBFNaK1KdcOGkmR1do66tUFB04n65mbAjnI1oLD7Rdjuua/ zA0KTxABVM3nPqRLREJ6zany2r9R9a90Z6UJNN5jEBs/zgQz9JOT1zyZu3IlGFuvTgW5 Obkh2ZOiXiRGvRSAfHKlm5tD2+LrhD1LVrcSw2T1FmDAPjvSp2NE10pt39l+YqaempCo U3xA== X-Forwarded-Encrypted: i=1; AHgh+RoX0f3yhmolHAlzOILovpPkUbGj1um0EuI2W3Ugwvsvhl5XbMkILkb0KISC6urC0HdRcqNRi4+O9fjlhvqQ3Q==@groups.io X-Gm-Message-State: AFuF++lNnMIxwG8n8e+tolS1v3X7MJy75gFQF9vPxupm+Hv3NCr9VbiG Ts397nutkZIc0f3d26LGch7o+dI43nBQeUdH3eLtjxLFaONy+Plx+VLLo0CrPA== X-Gm-Gg: AR+sD12juVEzzIHZUIIMPA/icSstKaL6crTiBGupZY3abJCGWtiSR88Hmc0G4VlUzoE DsSHzrm2Ck5mcdiEnQkDGvMBepz+Ckg862Bpvk2hFGKkg77KqV7WMY/R4fmafjBWbcYiadDLnHJ w0hFIfCL5xCeRRWsfMTQ//GIq4hxPJ3Shb0bbInPnGT9dERabzngQT9if83rPEwi9+HVGployLz +EjtRu7ohQ/b6Wl54Q2scqwtqQrc8LXYNquuLXV7OqSurL7TjQqL4TM6IuDcpiBtxlWcfUSvvgy I454WKIpJcmFnuOW2cRN/3M+jM1XS+GLWYpZJlZuinNnfVKrjTnesvCLdgbZKZ5h+heLsMAlvWY 9penQt1p0tr8iN/0qpU75bklx9pr9eL9lKcACg/i4l90hCRFA7UnNXKxJVES7QtS0RmG/PGcFJJ j5NPot0RnmGlEMQ/gZ79Aw8P/v4p8nqt4D2Sc/oPrUcO+tB8spPnz7iiuCJCCJ689GzqeV6HjHW iyS12XnkJcYgHmbcG688MCaT4Bf8MIxm+59gQ== X-Received: by 2002:a05:600c:6211:b0:499:621a:2ec2 with SMTP id 5b1f17b1804b1-499b82e8e9dmr74210185e9.3.1787301968300; Fri, 21 Aug 2026 01:46:08 -0700 (PDT) Received: from threads.localdomain ([83.106.158.114]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499b90e747esm22978115e9.4.2026.08.21.01.46.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Aug 2026 01:46:07 -0700 (PDT) From: Lucas Tanure To: u-boot@lists.u-boot-project.org Cc: neil.armstrong@linaro.org, trini@konsulko.com, ilias.apalodimas@linaro.org, funderscore@postmasteros.org, u-boot-amlogic@groups.io Subject: [PATCH v2 1/4] serial: meson: add Amlogic S4 UART support Date: Fri, 21 Aug 2026 09:46:00 +0100 Message-ID: <20260821084603.25974-2-tanure@linux.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260821084603.25974-1-tanure@linux.com> References: <20260821084603.25974-1-tanure@linux.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit List-Id: X-Webhook-Received: from 45-33-107-173.ip.linodeusercontent.com [45.33.107.173] by aws-us-west-2-korg-lkml-1.web.codeaurora.org with HTTPS for ; Mon, 24 Aug 2026 12:53:45 -0000 X-Groupsio-URL: https://groups.io/g/u-boot-amlogic/message/3049 The S4-generation UART (S4, T7, ...) derives its baud rate from the 24 MHz crystal divided by 2, selected via the XTAL_DIV2 bit in the baud rate register, while older SoCs divide the crystal by 3. Add the "amlogic,meson-s4-uart" compatible with driver data selecting the div-by-2 scheme, matching the Linux driver (meson_s4_uart_data) and the configuration the vendor BL2 programs on T7 hardware. Older SoCs keep the existing div-by-3 behaviour: Linux also uses div-by-2 on G12A, but both modes work there and switching would risk regressing boards that have shipped with div-by-3 for years. Also drain the transmitter before changing the baud rate so in-flight characters are not garbled, as the Linux driver does. Assisted-by: Claude:claude-fable-5 Signed-off-by: Lucas Tanure --- drivers/serial/serial_meson.c | 51 ++++++++++++++++++++++++++--------- 1 file changed, 38 insertions(+), 13 deletions(-) diff --git a/drivers/serial/serial_meson.c b/drivers/serial/serial_meson.c index cc71381f87e..d909fedcfc4 100644 --- a/drivers/serial/serial_meson.c +++ b/drivers/serial/serial_meson.c @@ -62,26 +62,49 @@ struct meson_serial_plat { #define AML_UART_REG5_USE_NEW_BAUD BIT(23) /* default 1 (use new baud rate register) */ #define AML_UART_REG5_BAUD_MASK 0x7fffff +/* Driver data flags */ +#define MESON_UART_XTAL_DIV2 BIT(0) + #if CONFIG_IS_ENABLED(DM_SERIAL) -static u32 meson_calc_baud_divisor(ulong src_rate, u32 baud) +static u32 meson_uart_xtal_div(struct udevice *dev) +{ + /* + * S4-generation UARTs (S4, T7, ...) derive the baud rate from the + * crystal divided by 2, older ones divide by 3. + */ + return (dev_get_driver_data(dev) & MESON_UART_XTAL_DIV2) ? 2 : 3; +} + +static u32 meson_calc_baud_divisor(struct udevice *dev, ulong src_rate, u32 baud) { /* * Usually src_rate is 24 MHz (from crystal) as clock source for serial - * device. Since 8 Mb/s is the maximum supported baud rate, use div by 3 - * to derive baud rate. This choice is used also in meson_serial_setbrg. + * device. Since 8 Mb/s is the maximum supported baud rate, use a + * divided crystal to derive the baud rate. This choice is used also in + * meson_serial_setbrg. */ - return DIV_ROUND_CLOSEST(src_rate / 3, baud) - 1; + return DIV_ROUND_CLOSEST(src_rate / meson_uart_xtal_div(dev), baud) - 1; } -static void meson_serial_set_baud(struct meson_uart *uart, ulong src_rate, u32 baud) +static void meson_serial_set_baud(struct udevice *dev, struct meson_uart *uart, + ulong src_rate, u32 baud) { /* - * Set crystal divided by 3 (regardless of device tree clock property) + * Set the divided crystal (regardless of device tree clock property) * as clock source and the corresponding divisor to approximate baud */ - u32 divisor = meson_calc_baud_divisor(src_rate, baud); + u32 divisor = meson_calc_baud_divisor(dev, src_rate, baud); u32 val = AML_UART_REG5_USE_XTAL_CLK | AML_UART_REG5_USE_NEW_BAUD | (divisor & AML_UART_REG5_BAUD_MASK); + + if (meson_uart_xtal_div(dev) == 2) + val |= AML_UART_REG5_XTAL_DIV2; + + /* Drain the transmitter before changing the baud rate */ + while ((readl(&uart->status) & (AML_UART_TX_EMPTY | AML_UART_XMIT_BUSY)) + != AML_UART_TX_EMPTY) + ; + writel(val, &uart->reg5); } @@ -109,7 +132,7 @@ static int meson_serial_probe(struct udevice *dev) return ret; ulong rate = clk_get_rate(&per_clk); - meson_serial_set_baud(uart, rate, CONFIG_BAUDRATE); + meson_serial_set_baud(dev, uart, rate, CONFIG_BAUDRATE); meson_serial_init(uart); return 0; @@ -165,8 +188,9 @@ static int meson_serial_setbrg(struct udevice *dev, const int baud) { /* * Change device baud rate if baud is reasonable (considering a 23 bit - * counter with an 8 MHz clock input) and the actual baud - * rate is within 2% of the requested value (2% is arbitrary). + * counter with an 8 MHz, or 12 MHz for XTAL_DIV2 devices, clock input) + * and the actual baud rate is within 2% of the requested value (2% is + * arbitrary). */ if (baud < 1 || baud > 8000000) return -EINVAL; @@ -179,14 +203,14 @@ static int meson_serial_setbrg(struct udevice *dev, const int baud) if (ret) return ret; ulong rate = clk_get_rate(&per_clk); - u32 divisor = meson_calc_baud_divisor(rate, baud); - u32 calc_baud = (rate / 3) / (divisor + 1); + u32 divisor = meson_calc_baud_divisor(dev, rate, baud); + u32 calc_baud = (rate / meson_uart_xtal_div(dev)) / (divisor + 1); u32 calc_err = baud > calc_baud ? baud - calc_baud : calc_baud - baud; if (((calc_err * 100) / baud) > 2) return -EINVAL; - meson_serial_set_baud(uart, rate, baud); + meson_serial_set_baud(dev, uart, rate, baud); return 0; } @@ -244,6 +268,7 @@ static const struct udevice_id meson_serial_ids[] = { { .compatible = "amlogic,meson-uart" }, { .compatible = "amlogic,meson-gx-uart" }, { .compatible = "amlogic,meson-a1-uart" }, + { .compatible = "amlogic,meson-s4-uart", .data = MESON_UART_XTAL_DIV2 }, { } }; -- 2.55.0