Commit 5d9176ed authored by Erwan Le Ray's avatar Erwan Le Ray Committed by Greg Kroah-Hartman
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serial: stm32: update PIO transmission 



Improves PIO transmission:
- Replaces the FIFO filling per character by a filling per blocks of
  characters, which provides better performances
- Replaces the active waiting loop by TX empty interrupt dynamic handling.
  TXE interrupt is now enabled when data has to be sent (ie when
  uart_circ is not empty), and inhibited when there is no more data to
  send (ie when uart_circ is empty).

Signed-off-by: default avatarErwan Le Ray <erwan.leray@st.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 4cc0ed62

drivers/tty/serial/stm32-usart.c

+13 −14
Original line number Diff line number Diff line
@@ -300,29 +300,28 @@ static void stm32_transmit_chars_pio(struct uart_port *port) 
	struct stm32_port *stm32_port = to_stm32_port(port);

	struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

	struct circ_buf *xmit = &port->state->xmit;

	unsigned int isr;

	int ret;



	if (stm32_port->tx_dma_busy) {

		stm32_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

		stm32_port->tx_dma_busy = false;

	}



	ret = readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr,

						isr,

						(isr & USART_SR_TXE),

						10, 100000);



	if (ret)

		dev_err(port->dev, "tx empty not set\n");



	stm32_set_bits(port, ofs->cr1, USART_CR1_TXEIE);



	while (!uart_circ_empty(xmit)) {

		/* Check that TDR is empty before filling FIFO */

		if (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))

			break;

		writel_relaxed(xmit->buf[xmit->tail], port->membase + ofs->tdr);

		xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);

		port->icount.tx++;

	}



	/* rely on TXE irq (mask or unmask) for sending remaining data */

	if (uart_circ_empty(xmit))

		stm32_clr_bits(port, ofs->cr1, USART_CR1_TXEIE);

	else

		stm32_set_bits(port, ofs->cr1, USART_CR1_TXEIE);

}



static void stm32_transmit_chars_dma(struct uart_port *port)

{

	struct stm32_port *stm32port = to_stm32_port(port);

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