serial: imx: Add DMA buffer configuration via DT

In order to optimize serial communication (performance/throughput VS
latency), we may need to tweak DMA period number and size. This adds
DT properties to configure those values before initialising DMA.
The defaults will stay the same as before.

[update documentation and commit message, rebase to current master,
switch back to DT instead of sysfs]

Signed-off-by: Fabien Lahoudere <fabien.lahoudere@collabora.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20210430175038.103226-2-sebastian.reichel@collabora.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/devicetree/bindings/serial/fsl-imx-uart.yaml b/Documentation/devicetree/bindings/serial/fsl-imx-uart.yaml
index 2b06c6ce4a75b29673d98f7b8cd99de12969c69e..9d949296a142500cfd99be6e34dbe54afe18e6dd 100644 (file)
--- a/Documentation/devicetree/bindings/serial/fsl-imx-uart.yaml
+++ b/Documentation/devicetree/bindings/serial/fsl-imx-uart.yaml
@@ -71,6 +71,18 @@ properties:
       received, and that the peripheral should invert its input using the
       INVR registers.
 
+  fsl,dma-info:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    minItems: 2
+    maxItems: 2
+    description: |
+      First cell contains the size of DMA buffer chunks, second cell contains
+      the amount of chunks used for the device. Multiplying both numbers is
+      the total size of memory used for receiving data.
+      When not being configured the system will use default settings, which
+      are sensible for most use cases. If you need low latency processing on
+      slow connections this needs to be configured appropriately.
+
   uart-has-rtscts: true
 
   rs485-rts-delay: true

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 4b838601cdce5f3e45c569afaed2eb0eef0e5a94..8b121cd869e945ae3d38af938b55fdf1a1cf781c 100644 (file)
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -225,6 +225,8 @@ struct imx_port {
        struct scatterlist      rx_sgl, tx_sgl[2];
        void                    *rx_buf;
        struct circ_buf         rx_ring;
+       unsigned int            rx_buf_size;
+       unsigned int            rx_period_length;
        unsigned int            rx_periods;
        dma_cookie_t            rx_cookie;
        unsigned int            tx_bytes;
@@ -1183,10 +1185,6 @@ static void imx_uart_dma_rx_callback(void *data)
        }
 }
 
-/* RX DMA buffer periods */
-#define RX_DMA_PERIODS 16
-#define RX_BUF_SIZE    (RX_DMA_PERIODS * PAGE_SIZE / 4)
-
 static int imx_uart_start_rx_dma(struct imx_port *sport)
 {
        struct scatterlist *sgl = &sport->rx_sgl;
@@ -1197,9 +1195,8 @@ static int imx_uart_start_rx_dma(struct imx_port *sport)
 
        sport->rx_ring.head = 0;
        sport->rx_ring.tail = 0;
-       sport->rx_periods = RX_DMA_PERIODS;
 
-       sg_init_one(sgl, sport->rx_buf, RX_BUF_SIZE);
+       sg_init_one(sgl, sport->rx_buf, sport->rx_buf_size);
        ret = dma_map_sg(dev, sgl, 1, DMA_FROM_DEVICE);
        if (ret == 0) {
                dev_err(dev, "DMA mapping error for RX.\n");
@@ -1316,7 +1313,8 @@ static int imx_uart_dma_init(struct imx_port *sport)
                goto err;
        }
 
-       sport->rx_buf = kzalloc(RX_BUF_SIZE, GFP_KERNEL);
+       sport->rx_buf_size = sport->rx_period_length * sport->rx_periods;
+       sport->rx_buf = kzalloc(sport->rx_buf_size, GFP_KERNEL);
        if (!sport->rx_buf) {
                ret = -ENOMEM;
                goto err;
@@ -2179,11 +2177,16 @@ static enum hrtimer_restart imx_trigger_stop_tx(struct hrtimer *t)
        return HRTIMER_NORESTART;
 }
 
+/* Default RX DMA buffer configuration */
+#define RX_DMA_PERIODS         16
+#define RX_DMA_PERIOD_LEN      (PAGE_SIZE / 4)
+
 static int imx_uart_probe(struct platform_device *pdev)
 {
        struct device_node *np = pdev->dev.of_node;
        struct imx_port *sport;
        void __iomem *base;
+       u32 dma_buf_conf[2];
        int ret = 0;
        u32 ucr1;
        struct resource *res;
@@ -2218,6 +2221,14 @@ static int imx_uart_probe(struct platform_device *pdev)
        if (of_get_property(np, "fsl,inverted-rx", NULL))
                sport->inverted_rx = 1;
 
+       if (!of_property_read_u32_array(np, "fsl,dma-info", dma_buf_conf, 2)) {
+               sport->rx_period_length = dma_buf_conf[0];
+               sport->rx_periods = dma_buf_conf[1];
+       } else {
+               sport->rx_period_length = RX_DMA_PERIOD_LEN;
+               sport->rx_periods = RX_DMA_PERIODS;
+       }
+
        if (sport->port.line >= ARRAY_SIZE(imx_uart_ports)) {
                dev_err(&pdev->dev, "serial%d out of range\n",
                        sport->port.line);