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[90.63.244.31]) by smtp.gmail.com with ESMTPSA id d20-20020a05600c34d400b0038caf684679sm9953386wmq.0.2022.04.07.07.03.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Apr 2022 07:03:02 -0700 (PDT) Message-ID: Date: Thu, 7 Apr 2022 16:03:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH 2/3] tty: serial: meson: Added 12Mhz as the clock source for calculating baud rate 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, Kevin Hilman , Jerome Brunet Cc: Greg Kroah-Hartman , Jiri Slaby , Martin Blumenstingl References: <20220407081355.13602-1-yu.tu@amlogic.com> <20220407081355.13602-3-yu.tu@amlogic.com> From: Neil Armstrong Organization: Baylibre In-Reply-To: <20220407081355.13602-3-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 07/04/2022 10:13, Yu Tu wrote: > Starting with the g12A chip, add a 12Mhz clock to calculate the baud > rate, since the BT module uses 3Mhz baud rate. 8Mhz calculations can > lead to baud rate bias, causing some problems. The commit message isn't clear enough, 12MHz is a new intermediate clock rate, not a new clock source of the UART module. Please explain 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. > > Signed-off-by: Yu Tu > --- > drivers/tty/serial/meson_uart.c | 25 +++++++++++++++++++++++-- > 1 file changed, 23 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c > index 8e59624935af..7e77693a1318 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; > + 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->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; > @@ -691,6 +703,7 @@ static int meson_uart_probe_clocks(struct platform_device *pdev, > > static int meson_uart_probe(struct platform_device *pdev) > { > + struct meson_uart_data *private_data; > struct resource *res_mem; > struct uart_port *port; > u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */ > @@ -733,6 +746,13 @@ static int meson_uart_probe(struct platform_device *pdev) > if (!port) > return -ENOMEM; > > + private_data = devm_kzalloc(&pdev->dev, sizeof(struct meson_uart_data), GFP_KERNEL); > + if (!private_data) > + return -ENOMEM; > + > + if ((bool)device_get_match_data(&pdev->dev)) > + private_data->has_xtal_div2 = true; It should be much cleaner to pass meson_uart_data to meson_uart_dt_match .data, and then you can retrieve device_get_match_data() and put the result into port->private_data. This will avoid a devm_kzalloc(). Then in meson_uart_change_speed() change the test to check for NULL private_data: if (private_data && private_data->has_xtal_div2) > + > ret = meson_uart_probe_clocks(pdev, port); > if (ret) > return ret; > @@ -749,6 +769,7 @@ static int meson_uart_probe(struct platform_device *pdev) > port->x_char = 0; > port->ops = &meson_uart_ops; > port->fifosize = fifosize; > + port->private_data = private_data; > > meson_ports[pdev->id] = port; > platform_set_drvdata(pdev, port); Neil