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Message-ID: <4b669bd6-e7bc-8cd9-ad60-03a31c7e8b1a@microchip.com>
Date: Mon, 12 Sep 2022 08:06:20 +0000
From: <Claudiu.Beznea@...rochip.com>
To: <Sergiu.Moga@...rochip.com>, <lee@...nel.org>,
<robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
<Nicolas.Ferre@...rochip.com>, <alexandre.belloni@...tlin.com>,
<richard.genoud@...il.com>, <radu_nicolae.pirea@....ro>,
<gregkh@...uxfoundation.org>, <broonie@...nel.org>,
<mturquette@...libre.com>, <sboyd@...nel.org>,
<jirislaby@...nel.org>, <admin@...iphile.com>,
<Kavyasree.Kotagiri@...rochip.com>, <Tudor.Ambarus@...rochip.com>
CC: <devicetree@...r.kernel.org>,
<linux-arm-kernel@...ts.infradead.org>,
<linux-kernel@...r.kernel.org>, <linux-spi@...r.kernel.org>,
<linux-serial@...r.kernel.org>, <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v2 12/13] tty: serial: atmel: Make the driver aware of the
existence of GCLK
On 06.09.2022 16:55, Sergiu Moga wrote:
> Previously, the atmel serial driver did not take into account the
> possibility of using the more customizable generic clock as its
> baudrate generator. Unless there is a Fractional Part available to
> increase accuracy, there is a high chance that we may be able to
> generate a baudrate closer to the desired one by using the GCLK as the
> clock source. Now, depending on the error rate between
> the desired baudrate and the actual baudrate, the serial driver will
> fallback on the generic clock. The generic clock must be provided
> in the DT node of the serial that may need a more flexible clock source.
>
> Signed-off-by: Sergiu Moga <sergiu.moga@...rochip.com>
> ---
>
>
>
> v1 -> v2:
> - take into account the different placement of the baudrate clock source
> into the IP's Mode Register (USART vs UART)
> - don't check for atmel_port->gclk != NULL
> - use clk_round_rate instead of clk_set_rate + clk_get_rate
> - remove clk_disable_unprepare from the end of the probe method
>
>
>
> drivers/tty/serial/atmel_serial.c | 52 ++++++++++++++++++++++++++++++-
> 1 file changed, 51 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 6aa01ca5489c..b2b6fd6ea2a5 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -15,6 +15,7 @@
> #include <linux/init.h>
> #include <linux/serial.h>
> #include <linux/clk.h>
> +#include <linux/clk-provider.h>
> #include <linux/console.h>
> #include <linux/sysrq.h>
> #include <linux/tty_flip.h>
> @@ -77,6 +78,8 @@ static void atmel_stop_rx(struct uart_port *port);
> #endif
>
> #define ATMEL_ISR_PASS_LIMIT 256
> +#define ERROR_RATE(desired_value, actual_value) \
> + ((int)(100 - ((desired_value) * 100) / (actual_value)))
>
> struct atmel_dma_buffer {
> unsigned char *buf;
> @@ -110,6 +113,7 @@ struct atmel_uart_char {
> struct atmel_uart_port {
> struct uart_port uart; /* uart */
> struct clk *clk; /* uart clock */
> + struct clk *gclk; /* uart generic clock */
> int may_wakeup; /* cached value of device_may_wakeup for times we need to disable it */
> u32 backup_imr; /* IMR saved during suspend */
> int break_active; /* break being received */
> @@ -2117,6 +2121,8 @@ static void atmel_serial_pm(struct uart_port *port, unsigned int state,
> * This is called on uart_close() or a suspend event.
> */
> clk_disable_unprepare(atmel_port->clk);
> + if (__clk_is_enabled(atmel_port->gclk))
> + clk_disable_unprepare(atmel_port->gclk);
> break;
> default:
> dev_err(port->dev, "atmel_serial: unknown pm %d\n", state);
> @@ -2131,7 +2137,8 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> {
> struct atmel_uart_port *atmel_port = to_atmel_uart_port(port);
> unsigned long flags;
> - unsigned int old_mode, mode, imr, quot, baud, div, cd, fp = 0;
> + unsigned int old_mode, mode, imr, quot, div, cd, fp = 0;
> + unsigned int baud, actual_baud, gclk_rate;
>
> /* save the current mode register */
> mode = old_mode = atmel_uart_readl(port, ATMEL_US_MR);
> @@ -2297,6 +2304,43 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
> cd &= 65535;
> }
>
> + /*
> + * If there is no Fractional Part, there is a high chance that
> + * we may be able to generate a baudrate closer to the desired one
> + * if we use the GCLK as the clock source driving the baudrate
> + * generator.
> + */
> + if (!atmel_port->has_frac_baudrate) {
> + if (__clk_is_enabled(atmel_port->gclk))
> + clk_disable_unprepare(atmel_port->gclk);
> + gclk_rate = clk_round_rate(atmel_port->gclk, 16 * baud);
> + actual_baud = clk_get_rate(atmel_port->clk) / (16 * cd);
> + if (gclk_rate && abs(ERROR_RATE(baud, actual_baud)) >
> + abs(ERROR_RATE(baud, gclk_rate / 16))) {
> + clk_set_rate(atmel_port->gclk, 16 * baud);
This is a personal taste: I would do like this:
ret = clk_prepare_enable();
if (ret)
goto clk_prepare_failure;
// and here the rest of the code...
> + if (!clk_prepare_enable(atmel_port->gclk)) {
> + if (atmel_port->is_usart) {
> + mode &= ~ATMEL_US_USCLKS;
> + mode |= ATMEL_US_USCLKS_GCLK;
> + } else {
> + mode &= ~ATMEL_UA_BRSRCCK;
> + mode |= ATMEL_UA_BRSRCCK_GCLK;
> + }
> +
> + /*
> + * Set the Clock Divisor for GCLK to 1.
> + * Since we were able to generate the smallest
> + * multiple of the desired baudrate times 16,
> + * then we surely can generate a bigger multiple
> + * with the exact error rate for an equally increased
> + * CD. Thus no need to take into account
> + * a higher value for CD.
> + */
> + cd = 1;
> + }
> + }
> + }
> +
clk_prepare_failure: // or other label name
> quot = cd | fp << ATMEL_US_FP_OFFSET;
>
> if (!(port->iso7816.flags & SER_ISO7816_ENABLED))
> @@ -2892,6 +2936,12 @@ static int atmel_serial_probe(struct platform_device *pdev)
> if (ret)
> goto err;
>
> + atmel_port->gclk = devm_clk_get_optional(&pdev->dev, "gclk");
> + if (IS_ERR(atmel_port->gclk)) {
> + ret = PTR_ERR(atmel_port->gclk);
> + goto err;
This should be:
goto err_clk_disable_unprepare;
to disable the peripheral clock previously enabled.
> + }
> +
> ret = atmel_init_port(atmel_port, pdev);
> if (ret)
> goto err_clk_disable_unprepare;
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