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H:BYAPR04MB5303.namprd04.prod.outlook.com; FPR:; SPF:None; LANG:en; PTR:InfoNoRecords; MX:1; A:1; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: Iw4UGXXdj5iEcDJjUvGkgFkCZX0W/Q8Uwq4KLRvSwUNgA4f2WmNNfOg/MSWdU8DJvJp+O2T2SnAuqiFxQt3sLW4deiySAwhy2U5po6QGNy2t5WruNMktEgdZ+gBKuqXlKGB566atFQPqXFDGxJh2qiVpc/kYsF+vZZs1hUlr9Grelzq2k/l3SPwTeUAeYIsqx/gbR22u59eL23gpUsKCGI4mHhaWgPQocAVxRGIGLe8n32uxRoku2F0oBcfrkujFmhIb5QPJgG/y6f9QEYGKFMj9ZlxC1A1QeBk92duSiRzf/F6urZEXsZqIvlSVNMaYSZUIh19q16sREhpDgfubXDVDsftUg5XriuJlt7uSuBf74CJJpejpx8Av7yNDRh6b3WbJB2J4R33w2q5fGYHL/YY7rXuBxyn/tHm7sBQ+iD8= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3d234eb3-a136-4cb8-4a3b-08d67d36cb0e X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Jan 2019 11:19:17.5577 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB5016 Cc: Palmer Dabbelt , U-Boot Mailing List , Alexander Graf , Christoph Hellwig , Paul Walmsley Subject: [U-Boot] [PATCH v2 08/11] drivers: serial_sifive: Fix baud rate calculation X-BeenThere: u-boot@lists.denx.de X-Mailman-Version: 2.1.18 Precedence: list List-Id: U-Boot discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: u-boot-bounces@lists.denx.de Sender: "U-Boot" From: Atish Patra Compute the baud rate multipler with more precision. Signed-off-by: Atish Patra Reviewed-by: Alexander Graf Reviewed-by: Lukas Auer --- drivers/serial/serial_sifive.c | 28 ++++++++++++++++++++++++++-- 1 file changed, 26 insertions(+), 2 deletions(-) diff --git a/drivers/serial/serial_sifive.c b/drivers/serial/serial_sifive.c index 341728a690..ea4d35d48c 100644 --- a/drivers/serial/serial_sifive.c +++ b/drivers/serial/serial_sifive.c @@ -33,16 +33,40 @@ struct uart_sifive { }; struct sifive_uart_platdata { - unsigned int clock; + unsigned long clock; int saved_input_char; struct uart_sifive *regs; }; +/** + * Find minimum divisor divides in_freq to max_target_hz; + * Based on uart driver n SiFive FSBL. + * + * f_baud = f_in / (div + 1) => div = (f_in / f_baud) - 1 + * The nearest integer solution requires rounding up as to not exceed + * max_target_hz. + * div = ceil(f_in / f_baud) - 1 + * = floor((f_in - 1 + f_baud) / f_baud) - 1 + * This should not overflow as long as (f_in - 1 + f_baud) does not exceed + * 2^32 - 1, which is unlikely since we represent frequencies in kHz. + */ +static inline unsigned int uart_min_clk_divisor(unsigned long in_freq, + unsigned long max_target_hz) +{ + unsigned long quotient = + (in_freq + max_target_hz - 1) / (max_target_hz); + /* Avoid underflow */ + if (quotient == 0) + return 0; + else + return quotient - 1; +} + /* Set up the baud rate in gd struct */ static void _sifive_serial_setbrg(struct uart_sifive *regs, unsigned long clock, unsigned long baud) { - writel((u32)((clock / baud) - 1), ®s->div); + writel((uart_min_clk_divisor(clock, baud)), ®s->div); } static void _sifive_serial_init(struct uart_sifive *regs)