[PATCH v2 4/4] serial: stm32: add FIFO threshold configuration

Erwan Le Ray
2021-04-13T17:40:44Z

From: Fabrice Gasnier <fabrice.gasnier@foss.st.com>

Add the support for two optional DT properties, to configure RX and TX
FIFO thresholds:
- rx-threshold
- tx-threshold
This replaces hard-coded 8 bytes threshold. Keep 8 as the default value if
not specified, for backward compatibility.

Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>

Changes in v2:
Change added properties naming as proposed by Rob Herring.

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 4d277804c63e..409cfd15a933 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -312,7 +312,7 @@ static void stm32_usart_tx_interrupt_enable(struct uart_port *port)
* Enables TX FIFO threashold irq when FIFO is enabled,
* or TX empty irq when FIFO is disabled
*/
- if (stm32_port->fifoen)
+ if (stm32_port->fifoen && stm32_port->txftcfg >= 0)
stm32_usart_set_bits(port, ofs->cr3, USART_CR3_TXFTIE);
else
stm32_usart_set_bits(port, ofs->cr1, USART_CR1_TXEIE);
@@ -323,7 +323,7 @@ static void stm32_usart_tx_interrupt_disable(struct uart_port *port)
struct stm32_port *stm32_port = to_stm32_port(port);
const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

- if (stm32_port->fifoen)
+ if (stm32_port->fifoen && stm32_port->txftcfg >= 0)
stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_TXFTIE);
else
stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_TXEIE);
@@ -801,9 +801,10 @@ static void stm32_usart_set_termios(struct uart_port *port,
cr3 = readl_relaxed(port->membase + ofs->cr3);
cr3 &= USART_CR3_TXFTIE | USART_CR3_RXFTIE;
if (stm32_port->fifoen) {
- cr3 &= ~(USART_CR3_TXFTCFG_MASK | USART_CR3_RXFTCFG_MASK);
- cr3 |= USART_CR3_TXFTCFG_HALF << USART_CR3_TXFTCFG_SHIFT;
- cr3 |= USART_CR3_RXFTCFG_HALF << USART_CR3_RXFTCFG_SHIFT;
+ if (stm32_port->txftcfg >= 0)
+ cr3 |= stm32_port->txftcfg << USART_CR3_TXFTCFG_SHIFT;
+ if (stm32_port->rxftcfg >= 0)
+ cr3 |= stm32_port->rxftcfg << USART_CR3_RXFTCFG_SHIFT;
}

if (cflag & CSTOPB)
@@ -833,7 +834,8 @@ static void stm32_usart_set_termios(struct uart_port *port,
, bits);

if (ofs->rtor != UNDEF_REG && (stm32_port->rx_ch ||
- stm32_port->fifoen)) {
+ (stm32_port->fifoen &&
+ stm32_port->rxftcfg >= 0))) {
if (cflag & CSTOPB)
bits = bits + 3; /* 1 start bit + 2 stop bits */
else
@@ -1021,6 +1023,39 @@ static const struct uart_ops stm32_uart_ops = {
.verify_port = stm32_usart_verify_port,
};

+/*
+ * STM32H7 RX & TX FIFO threshold configuration (CR3 RXFTCFG / TXFTCFG)
+ * Note: 1 isn't a valid value in RXFTCFG / TXFTCFG. In this case,
+ * RXNEIE / TXEIE can be used instead of threshold irqs: RXFTIE / TXFTIE.
+ * So, RXFTCFG / TXFTCFG bitfields values are encoded as array index + 1.
+ */
+static const u32 stm32h7_usart_fifo_thresh_cfg[] = { 1, 2, 4, 8, 12, 14, 16 };
+
+static void stm32_usart_get_ftcfg(struct platform_device *pdev, const char *p,
+ int *ftcfg)
+{
+ u32 bytes, i;
+
+ /* DT option to get RX & TX FIFO threshold (default to 8 bytes) */
+ if (of_property_read_u32(pdev->dev.of_node, p, &bytes))
+ bytes = 8;
+
+ for (i = 0; i < ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg); i++)
+ if (stm32h7_usart_fifo_thresh_cfg[i] >= bytes)
+ break;
+ if (i >= ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg))
+ i = ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg) - 1;
+
+ dev_dbg(&pdev->dev, "%s set to %d bytes\n", p,
+ stm32h7_usart_fifo_thresh_cfg[i]);
+
+ /* Provide FIFO threshold ftcfg (1 is invalid: threshold irq unused) */
+ if (i)
+ *ftcfg = i - 1;
+ else
+ *ftcfg = -EINVAL;
+}
+
static void stm32_usart_deinit_port(struct stm32_port *stm32port)
{
clk_disable_unprepare(stm32port->clk);
@@ -1057,6 +1092,12 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
of_property_read_bool(pdev->dev.of_node, "rx-tx-swap");

stm32port->fifoen = stm32port->info->cfg.has_fifo;
+ if (stm32port->fifoen) {
+ stm32_usart_get_ftcfg(pdev, "rx-threshold",
+ &stm32port->rxftcfg);
+ stm32_usart_get_ftcfg(pdev, "tx-threshold",
+ &stm32port->txftcfg);
+ }

res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
port->membase = devm_ioremap_resource(&pdev->dev, res);
diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index 77d1ac082e89..07ac291328cd 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -216,12 +216,6 @@ struct stm32_usart_info stm32h7_info = {
#define USART_CR3_TXFTCFG_MASK GENMASK(31, 29) /* H7 */
#define USART_CR3_TXFTCFG_SHIFT 29 /* H7 */

-/* TX FIFO threashold set to half of its depth */
-#define USART_CR3_TXFTCFG_HALF 0x2
-
-/* RX FIFO threashold set to half of its depth */
-#define USART_CR3_RXFTCFG_HALF 0x2
-
/* USART_GTPR */
#define USART_GTPR_PSC_MASK GENMASK(7, 0)
#define USART_GTPR_GT_MASK GENMASK(15, 8)
@@ -273,6 +267,8 @@ struct stm32_port {
bool hw_flow_control;
bool swap; /* swap RX & TX pins */
bool fifoen;
+ int rxftcfg; /* RX FIFO threshold CFG */
+ int txftcfg; /* TX FIFO threshold CFG */
bool wakeup_src;
int rdr_mask; /* receive data register mask */
struct mctrl_gpios *gpios; /* modem control gpios */
--
2.17.1