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Tue, 24 Feb 2026 22:59:21 -0800 From: Kartik Rajput To: , , , , , , , , , , CC: Kartik Rajput Subject: [PATCH 1/4] serial: amba-pl011: Introduce skip_ibrd_fbrd vendor flag Date: Wed, 25 Feb 2026 12:29:11 +0530 Message-ID: <20260225065915.341522-2-kkartik@nvidia.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260225065915.341522-1-kkartik@nvidia.com> References: <20260225065915.341522-1-kkartik@nvidia.com> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH2PEPF00000142:EE_|DM4PR12MB6301:EE_ X-MS-Office365-Filtering-Correlation-Id: 50cb81f8-c4b7-48e2-72d5-08de743b7142 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|36860700013|82310400026|376014|7416014|921020; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?dvt3O28EHbj8tZwvqBrvfldNSBHPei3Pvnu2AAgdjbzcyWBrycoDVcMEMtr6?= =?us-ascii?Q?7A+NAIzB69Y9HvFwZmXhFMojNsa9ZHqQpPZYVL2Bi9G7QHQkRajmVqT+dwZv?= =?us-ascii?Q?mTZq/NZtWslf2Eih/uIS3bCYZpp8EEEeDshRYhxw9s/111DsSL11FRZl+wsM?= =?us-ascii?Q?osde1DzFcsxEF82Q2qeVSLNXHS6b+xstLti1zs9kxDERAlA/nQigsY50sTJX?= =?us-ascii?Q?uJtQHvJpjF+y8P09veHOK6zTnpF7tg0FgXdxpX75+2pdRm201N486ua2HZIY?= =?us-ascii?Q?JxPG3oqs0yseGcww1HbO6xnQiRl3JZruI1uPogOV2pc+L7IGmBxTdsNuy6G2?= =?us-ascii?Q?Z4dKI6Kqmeid9uUIDfD5XFvXkVLp4sUAkAWkAgGPspR1unEFmbIf2zU5GN4Y?= =?us-ascii?Q?C/0WgHLzUnkp0Kzs/pcgxTsRjrY8U5WkNAT8f1Sko4uCCSBLvPJE1qLr7HHA?= =?us-ascii?Q?vXpfMx/jKtpVzJmCMONjkFSng+F4vLNNooFv7q6Muve1ielR3TP6Cr2QZdk3?= =?us-ascii?Q?QGoxV9rmI4/iYrQvP5l11uym6nWXYBc2rv8jC4PD0OixaXPvKRkWLuPDYv4c?= =?us-ascii?Q?vN1Nv506wxRoeEN8I2O2IkTHIp6KWr/707uXggq1nXIvQVMHB6SOcIEUL2ar?= =?us-ascii?Q?upMCn6GfcFbBkzPMOOSH9Nvd3+D15K8COv51XJc5mrZze0LW5qY29DgoHBOz?= =?us-ascii?Q?kVp/ceP8oRfCc5Nkfu4BgrXu4cBPdeKykMoXLFwuG0/GM1cvLeSh6nrWHWAR?= =?us-ascii?Q?AOrjxq1c+sOG2V+LF000L4YSUaDqmc01JjJSbhEynUTje3V4NRiLstzrPkIs?= =?us-ascii?Q?KsClfG/gvuRSMZOJiKvyu5KBnR3eisfdTP8UlA9R6MPEHDx45aoVfLvcsYHL?= =?us-ascii?Q?UM+PPkcEPz/BKj5VhBwIve4dXCnrVEMxiQEztGJss3CV+PMHW3C9G5NctbIx?= =?us-ascii?Q?kf4XpkWkKgzCoGBIulHr8P3dSodKNIq25h9hm7ehgTBitqwRKQ76gaY7KIeJ?= =?us-ascii?Q?l18jJEVcVm0AvGcfM/2pRbjxSGePmxYa8TkmwscY6e+dFA9zncI+o4G12+pc?= =?us-ascii?Q?FKVEHvwSfu77eZjqL32NRI55derdCuLiMbq8m5edKQ1srR6Ud/+90RzZrZ31?= =?us-ascii?Q?lMFhcIdGF2C9+2vyZiqa5m5mqBc9GhLyieso0Me1c1o7EDlwSzujqI3AF637?= =?us-ascii?Q?C7SBfYBzruiMngpmNbBtLNB1LlUbI0UfRWr7eeKM6GzHoNbdfCZz0J5mNiPm?= =?us-ascii?Q?4MHy5Nvi1MTQ6zR8Rw1p7UEktECk1Z8gZxZdUmimxk2K9h+HrFSAq0B1Q/Nq?= =?us-ascii?Q?XxFi0WZGoR0zLMuTM87toiR9Dajg6wvqGzKCIIO1J/oSaVmJotibGsKUd845?= =?us-ascii?Q?PcWjtk3W8gHk7DgUlJtxRoZzD288QyKK/ma42fDseG+y09uHTsi5E/b8JyOe?= =?us-ascii?Q?ir5nk944v4lX293RBdFWscBdoKR/RdfOiQxmHUDu6kj3aw5WiqNyHP7+J8RE?= =?us-ascii?Q?dMOWkJD9o6PTafH0JZB/Ksmy5u/r9ZCmYF85a2bjKzKxkU1RsN9KNXnXLUWv?= =?us-ascii?Q?pY97lWixPAV2i3QuuEZMGYQYgyO0vNxpCAEixdZMMWyb1MCE525MC9IoDXgk?= =?us-ascii?Q?Udjkv1EVHdjahqvTlD9Og3aZwhpzJnpjbvDmZcG2HhpYwcaivo7etLeArve7?= =?us-ascii?Q?up8XYQ+ENIhuA+T67mu6yfrcALQ=3D?= X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(1800799024)(36860700013)(82310400026)(376014)(7416014)(921020);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: AqUEteG825520uuJ7Ts2fTqAyusL5p9udmdrnldoHcBLLsnB4KapvlFsPmITmEQ3ah9JAD687pCp4FoX63eFI/0p5XahKmfrv0y31JcDqO+59mCJrIRAYpNAczP4NsZBBaPT0f7HbJtbymBgZa7s4iTk283DA/JykpjAOQ/mvxWVPn52NcM78rADBuCHUQddOxGbRFW51UsKUEG+Nw/NaadtNcjZHrpQmx7IRqgjlLVUgKPGhgHKTPrt2h7+z1gQQM3X88y8WViNcBELKGFVxyHFKeyG7FLGsIxrVURzAteYAkBzWkYyOG5GM7xaw/RISLLcLzsRmsWUxxHhmPlXMLQ58hUTPYwgIyEF2SNHmSkI9o1F28ujJiGCtpasRC9r55s8eefaj2KWx5SMKIcuwjKeho753k1y/LO55d6tEflBexjPzbZWzvpBUfVuZ7Yl X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Feb 2026 06:59:38.3575 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 50cb81f8-c4b7-48e2-72d5-08de743b7142 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: CH2PEPF00000142.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB6301 The NVIDIA Tegra264 UART has a broken fractional baud rate divisor register. Using IBRD and FBRD may cause the baud rate to fall outside the required tolerance. Introduce the skip_ibrd_fbrd vendor flag to skip IBRD/FBRD programming. When set, the baud rate is derived directly from the UART clock rate using a fixed divisor. Signed-off-by: Kartik Rajput --- drivers/tty/serial/amba-pl011.c | 53 +++++++++++++++++++-------------- 1 file changed, 31 insertions(+), 22 deletions(-) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 7f17d288c807..79e1c937a600 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -114,6 +114,7 @@ struct vendor_data { bool cts_event_workaround; bool always_enabled; bool fixed_options; + bool skip_ibrd_fbrd; unsigned int (*get_fifosize)(struct amba_device *dev); }; @@ -2115,11 +2116,6 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios, uap->dmarx.poll_rate = DIV_ROUND_UP(10000000, baud); #endif - if (baud > port->uartclk / 16) - quot = DIV_ROUND_CLOSEST(port->uartclk * 8, baud); - else - quot = DIV_ROUND_CLOSEST(port->uartclk * 4, baud); - switch (termios->c_cflag & CSIZE) { case CS5: lcr_h = UART01x_LCRH_WLEN_5; @@ -2190,21 +2186,28 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios, old_cr &= ~ST_UART011_CR_OVSFACT; } - /* - * Workaround for the ST Micro oversampling variants to - * increase the bitrate slightly, by lowering the divisor, - * to avoid delayed sampling of start bit at high speeds, - * else we see data corruption. - */ - if (uap->vendor->oversampling) { - if (baud >= 3000000 && baud < 3250000 && quot > 1) - quot -= 1; - else if (baud > 3250000 && quot > 2) - quot -= 2; + if (!uap->vendor->skip_ibrd_fbrd) { + if (baud > port->uartclk / 16) + quot = DIV_ROUND_CLOSEST(port->uartclk * 8, baud); + else + quot = DIV_ROUND_CLOSEST(port->uartclk * 4, baud); + + /* + * Workaround for the ST Micro oversampling variants to + * increase the bitrate slightly, by lowering the divisor, + * to avoid delayed sampling of start bit at high speeds, + * else we see data corruption. + */ + if (uap->vendor->oversampling) { + if (baud >= 3000000 && baud < 3250000 && quot > 1) + quot -= 1; + else if (baud > 3250000 && quot > 2) + quot -= 2; + } + /* Set baud rate */ + pl011_write(quot & 0x3f, uap, REG_FBRD); + pl011_write(quot >> 6, uap, REG_IBRD); } - /* Set baud rate */ - pl011_write(quot & 0x3f, uap, REG_FBRD); - pl011_write(quot >> 6, uap, REG_IBRD); /* * ----------v----------v----------v----------v----- @@ -2374,6 +2377,7 @@ static void pl011_console_get_options(struct uart_amba_port *uap, int *baud, int *parity, int *bits) { unsigned int lcr_h, ibrd, fbrd; + unsigned int clkdiv; if (!(pl011_read(uap, REG_CR) & UART01x_CR_UARTEN)) return; @@ -2393,10 +2397,15 @@ static void pl011_console_get_options(struct uart_amba_port *uap, int *baud, else *bits = 8; - ibrd = pl011_read(uap, REG_IBRD); - fbrd = pl011_read(uap, REG_FBRD); + if (uap->vendor->skip_ibrd_fbrd) { + clkdiv = 64; + } else { + ibrd = pl011_read(uap, REG_IBRD); + fbrd = pl011_read(uap, REG_FBRD); + clkdiv = 64 * ibrd + fbrd; + } - *baud = uap->port.uartclk * 4 / (64 * ibrd + fbrd); + *baud = uap->port.uartclk * 4 / clkdiv; if (uap->vendor->oversampling && (pl011_read(uap, REG_CR) & ST_UART011_CR_OVSFACT)) -- 2.43.0