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FPR:; SPF:None; LANG:en; PTR:InfoNoRecords; MX:1; A:1; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: IhgOtE9fRh6mI7qaofmEqrMbmZqLI1rH0+6zCov1ZvKopcDmCfnNivi8fsnJKKDp0oFEs2liN8y1aj2bwUSS9PEPLt4wVsA3xS0Ah0OHVj2uY0zVVHm/Krd/GZ7ToGtTcE23mxtDB74WjUm7Z0+138U5m0E3EZN0wGE7tm/Zzm9S8nmr7bSwttG1nSh1n8MBeRWNfTot1F/4ELwFqL+EPfEbbtOjn7chN9410KdVJ6CSy3hOB+H+439JbrwNU/icFukt0vP8iIXORgSgyfu2Wl2PhURJTv/QGbjn2LQ6DKCUps7ZPx58yxkuPQAE6VIYt5C2lIxxRe3kV7DZZOXECy13Gp7Qoz6pDkkgK+a7l0xThCE/5tsenPDuwwethvUCvYp/0FYyZ1kdMavDEYUsy+GaXzEvy67JEjjHNnWgpkg= MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: a3b833fa-2c5e-44c5-8188-08d68e586e1a X-MS-Exchange-CrossTenant-originalarrivaltime: 09 Feb 2019 06:32:53.5142 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2SPR01MB0008 Cc: Palmer Dabbelt , Alexander Graf , U-Boot Mailing List Subject: [U-Boot] [PATCH v6 11/16] 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 Signed-off-by: Anup Patel 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)