[Adding Uwe and Stefan, who have been working with RS485 on i.MX lately.
Maybe we should an entry for drivers/tty/serial/imx.c in MAINTAINERS file? ]
On Mon, Apr 23, 2018 at 9:14 AM, Einar Vading <einar.vading@xxxxxxxx> wrote:
> When using RS485 in half duplex mode the RTS line is typically used to
> toggle receive/transmit on the transceiver IC. As some protocols (OSDP
> f.ex.) specify that the slave should respond within some short time period,
> it is important that the RTS line toggles the transceiver from transmit
> mode to receive mode within that time.
>
> This change puts a pm_qos requirement on CPU_DMA_LATENCY when in RS485 tx
> mode so that CPU wake times won't cause to long delays.
>
> Signed-off-by: Einar Vading <einarv@xxxxxxxx>
> ---
> Changes in v2:
> - Uses a workqueue to avoid setting pm_qos from hard IRQ.
>
> drivers/tty/serial/imx.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index f370c1cf4f27..5967f98f1686 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -30,6 +30,8 @@
> #include <linux/of_device.h>
> #include <linux/io.h>
> #include <linux/dma-mapping.h>
> +#include <linux/pm_qos.h>
> +#include <linux/workqueue.h>
>
> #include <asm/irq.h>
> #include <linux/platform_data/serial-imx.h>
> @@ -225,6 +227,9 @@ struct imx_port {
> unsigned int dma_tx_nents;
> unsigned int saved_reg[10];
> bool context_saved;
> + u32 latency;
> + struct pm_qos_request pm_qos_req;
> + struct work_struct qos_work;
> };
>
> struct imx_port_ucrs {
> @@ -457,6 +462,8 @@ static void imx_uart_stop_tx(struct uart_port *port)
> ucr4 = imx_uart_readl(sport, UCR4);
> ucr4 &= ~UCR4_TCEN;
> imx_uart_writel(sport, ucr4, UCR4);
> + sport->latency = PM_QOS_DEFAULT_VALUE;
> + schedule_work(&sport->qos_work);
> }
> }
>
> @@ -657,6 +664,9 @@ static void imx_uart_start_tx(struct uart_port *port)
> if (port->rs485.flags & SER_RS485_ENABLED) {
> u32 ucr2;
>
> + sport->latency = 0;
> + schedule_work(&sport->qos_work);
> +
> ucr2 = imx_uart_readl(sport, UCR2);
> if (port->rs485.flags & SER_RS485_RTS_ON_SEND)
> imx_uart_rts_active(sport, &ucr2);
> @@ -1852,6 +1862,14 @@ static int imx_uart_rs485_config(struct uart_port *port,
> return 0;
> }
>
> +static void imx_qos_work(struct work_struct *work)
> +{
> + struct imx_port *sport;
> +
> + sport = container_of(work, struct imx_port, qos_work);
> + pm_qos_update_request(&sport->pm_qos_req, sport->latency);
> +}
> +
> static const struct uart_ops imx_uart_pops = {
> .tx_empty = imx_uart_tx_empty,
> .set_mctrl = imx_uart_set_mctrl,
> @@ -1868,6 +1886,7 @@ static const struct uart_ops imx_uart_pops = {
> .type = imx_uart_type,
> .config_port = imx_uart_config_port,
> .verify_port = imx_uart_verify_port,
> +
Minor nit: this change is unrelated.
> #if defined(CONFIG_CONSOLE_POLL)
> .poll_init = imx_uart_poll_init,
> .poll_get_char = imx_uart_poll_get_char,
> @@ -2335,6 +2354,10 @@ static int imx_uart_probe(struct platform_device *pdev)
> }
> }
>
> + pm_qos_add_request(&sport->pm_qos_req, PM_QOS_CPU_DMA_LATENCY,
> + PM_QOS_DEFAULT_VALUE);
> + INIT_WORK(&sport->qos_work, imx_qos_work);
> +
> imx_uart_ports[sport->port.line] = sport;
>
> platform_set_drvdata(pdev, sport);
> @@ -2346,6 +2369,8 @@ static int imx_uart_remove(struct platform_device *pdev)
> {
> struct imx_port *sport = platform_get_drvdata(pdev);
>
> + pm_qos_remove_request(&sport->pm_qos_req);
> +
> return uart_remove_one_port(&imx_uart_uart_driver, &sport->port);
> }
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