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([2001:861:44c0:66c0:3ce1:1ed1:5e14:cd49]) by smtp.gmail.com with ESMTPSA id o10-20020a5d47ca000000b0020a992ce354sm1930835wrc.76.2022.04.22.05.30.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Apr 2022 05:30:07 -0700 (PDT) Message-ID: Date: Fri, 22 Apr 2022 14:30:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH V3 1/2] tty: serial: meson: Add a 12MHz internal clock rate to calculate baud rate in order to meet the baud rate requirements of special BT modules Content-Language: en-US To: Yu Tu , linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Kevin Hilman , Jerome Brunet Cc: Jiri Slaby , Martin Blumenstingl References: <20220422111320.19234-1-yu.tu@amlogic.com> <20220422111320.19234-2-yu.tu@amlogic.com> From: Neil Armstrong Organization: Baylibre In-Reply-To: <20220422111320.19234-2-yu.tu@amlogic.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22/04/2022 13:13, Yu Tu wrote: > A /2 divider over XTAL was introduced since G12A, and is preferred > to be used over the still present /3 divider since it provides much > closer frequencies vs the request baudrate. Especially the BT module > uses 3Mhz baud rate. 8Mhz calculations can lead to baud rate bias, > causing some problems. > > Signed-off-by: Yu Tu > --- > drivers/tty/serial/meson_uart.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c > index 8e59624935af..58bd2723c004 100644 > --- a/drivers/tty/serial/meson_uart.c > +++ b/drivers/tty/serial/meson_uart.c > @@ -68,6 +68,7 @@ > #define AML_UART_BAUD_MASK 0x7fffff > #define AML_UART_BAUD_USE BIT(23) > #define AML_UART_BAUD_XTAL BIT(24) > +#define AML_UART_BAUD_XTAL_DIV2 BIT(27) > > #define AML_UART_PORT_NUM 12 > #define AML_UART_PORT_OFFSET 6 > @@ -80,6 +81,10 @@ static struct uart_driver meson_uart_driver; > > static struct uart_port *meson_ports[AML_UART_PORT_NUM]; > > +struct meson_uart_data { > + bool has_xtal_div2; > +}; > + > static void meson_uart_set_mctrl(struct uart_port *port, unsigned int mctrl) > { > } > @@ -293,13 +298,20 @@ static int meson_uart_startup(struct uart_port *port) > > static void meson_uart_change_speed(struct uart_port *port, unsigned long baud) > { > - u32 val; > + const struct meson_uart_data *private_data = port->private_data; > + u32 val = 0; > > while (!meson_uart_tx_empty(port)) > cpu_relax(); > > if (port->uartclk == 24000000) { > - val = DIV_ROUND_CLOSEST(port->uartclk / 3, baud) - 1; > + unsigned int xtal_div = 3; > + > + if (private_data && private_data->has_xtal_div2) { > + xtal_div = 2; > + val |= AML_UART_BAUD_XTAL_DIV2; > + } > + val |= DIV_ROUND_CLOSEST(port->uartclk / xtal_div, baud) - 1; > val |= AML_UART_BAUD_XTAL; > } else { > val = DIV_ROUND_CLOSEST(port->uartclk / 4, baud) - 1; > @@ -749,6 +761,7 @@ static int meson_uart_probe(struct platform_device *pdev) > port->x_char = 0; > port->ops = &meson_uart_ops; > port->fifosize = fifosize; > + port->private_data = (void *)device_get_match_data(&pdev->dev); > > meson_ports[pdev->id] = port; > platform_set_drvdata(pdev, port); Reviewed-by: Neil Armstrong