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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: rWa+XNMbrZIZ93MSlE6ctgchhBm0fWmfKsqxhzT+ppYttshqFQUYY50aYmCT3FwBFWarwh9+pexKsbLALKT7FM5Fl+x6FN3svLnJlYcIdTgK7bNotkKAP87L6MnC+fR6+exQghzEzRQ4c897OaDMkF3uyKRbNvRFXu2Xg7A7HwxCirFlVy1kd7FSN57tHlukYTzq6BbRlvtJV2OJR9wwrLp4eOcqunzl40FTVCruW1pC710Q2zx6oI5Z2RxuURC0W2PUyxR4Nmvn5IRoHX3DEaPUiAasCGqzdnOmOkhSJSYyioN34cOGWO3ZrrhI0WLtViKURvlfQS6SDxKGVU6SwKdXC+t0yC1R56447K0QTCzGEZzGG1LWgE4vKBGwRJ23mZfuSvyDQCD88U+wdRQoH7EqbiL6U19H1KDq5mK/dIY= spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: f3053cb0-7e3a-4057-6719-08d67c680463 X-MS-Exchange-CrossTenant-originalarrivaltime: 17 Jan 2019 10:39:07.8444 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR04MB4744 X-Mailman-Approved-At: Thu, 17 Jan 2019 12:20:43 +0000 Cc: Palmer Dabbelt , U-Boot Mailing List , Alexander Graf , Christoph Hellwig , Paul Walmsley Subject: [U-Boot] [PATCH 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 --- 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)