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Thu, 12 Jul 2018 02:01:39 +0000 Date: Thu, 12 Jul 2018 09:59:40 +0800 From: Jisheng Zhang To: Andy Shevchenko , Greg Kroah-Hartman , Jiri Slaby Cc: linux-arm-kernel@lists.infradead.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v6 3/3] serial: 8250_dw: add fractional divisor support Message-ID: <20180712095940.20859423@xhacker.debian> In-Reply-To: <20180712095504.4d9583ce@xhacker.debian> References: <20180712095504.4d9583ce@xhacker.debian> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Originating-IP: [124.74.246.114] X-ClientProxiedBy: MR2P264CA0023.FRAP264.PROD.OUTLOOK.COM (2603:10a6:500:1::35) To CY4PR03MB2629.namprd03.prod.outlook.com (2603:10b6:903:75::8) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: b6a9e9fd-3086-4696-79d4-08d5e79b6a05 X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652040)(8989117)(5600053)(711020)(4534165)(4627221)(201703031133081)(201702281549075)(8990107)(2017052603328)(7153060)(7193020);SRVR:CY4PR03MB2629; 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The fractional divisor width is 4bits ~ 6bits. Now the preparation is done, it's easy to add the feature support. This patch firstly tries to get the fractional divisor width during probe, then setups dw specific get_divisor() and set_divisor() hook. Signed-off-by: Jisheng Zhang Reviewed-by: Andy Shevchenko --- drivers/tty/serial/8250/8250_dw.c | 45 +++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index fa8a00e8c9c6..5a60c4814d62 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -31,6 +31,7 @@ /* Offsets for the DesignWare specific registers */ #define DW_UART_USR 0x1f /* UART Status Register */ +#define DW_UART_DLF 0xc0 /* Divisor Latch Fraction Register */ #define DW_UART_CPR 0xf4 /* Component Parameter Register */ #define DW_UART_UCV 0xf8 /* UART Component Version */ @@ -55,6 +56,7 @@ struct dw8250_data { u8 usr_reg; + u8 dlf_size; int line; int msr_mask_on; int msr_mask_off; @@ -366,6 +368,37 @@ static bool dw8250_idma_filter(struct dma_chan *chan, void *param) return param == chan->device->dev->parent; } +/* + * divisor = div(I) + div(F) + * "I" means integer, "F" means fractional + * quot = div(I) = clk / (16 * baud) + * frac = div(F) * 2^dlf_size + * + * let rem = clk % (16 * baud) + * we have: div(F) * (16 * baud) = rem + * so frac = 2^dlf_size * rem / (16 * baud) = (rem << dlf_size) / (16 * baud) + */ +static unsigned int dw8250_get_divisor(struct uart_port *p, + unsigned int baud, + unsigned int *frac) +{ + unsigned int quot, rem, base_baud = baud * 16; + struct dw8250_data *d = p->private_data; + + quot = p->uartclk / base_baud; + rem = p->uartclk % base_baud; + *frac = DIV_ROUND_CLOSEST(rem << d->dlf_size, base_baud); + + return quot; +} + +static void dw8250_set_divisor(struct uart_port *p, unsigned int baud, + unsigned int quot, unsigned int quot_frac) +{ + dw8250_writel_ext(p, DW_UART_DLF, quot_frac); + serial8250_do_set_divisor(p, baud, quot, quot_frac); +} + static void dw8250_quirks(struct uart_port *p, struct dw8250_data *data) { if (p->dev->of_node) { @@ -426,6 +459,18 @@ static void dw8250_setup_port(struct uart_port *p) dev_dbg(p->dev, "Designware UART version %c.%c%c\n", (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff); + dw8250_writel_ext(p, DW_UART_DLF, ~0U); + reg = dw8250_readl_ext(p, DW_UART_DLF); + dw8250_writel_ext(p, DW_UART_DLF, 0); + + if (reg) { + struct dw8250_data *d = p->private_data; + + d->dlf_size = fls(reg); + p->get_divisor = dw8250_get_divisor; + p->set_divisor = dw8250_set_divisor; + } + reg = dw8250_readl_ext(p, DW_UART_CPR); if (!reg) return; -- 2.18.0