Commit 9a135f16 authored by Valentin Caron's avatar Valentin Caron Committed by Greg Kroah-Hartman
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serial: stm32: rework TX DMA state condition 



TX DMA state condition is handled by tx_dma_busy boolean.
This boolean is set when dma descriptor is requested and reset when dma
channel is stopped (dma_terminate).

In stm32_usart_serial_remove(), stm32_usart_stop_tx() and
stm32_usart_transmit_chars_dma() fallback error case, DMA channel is
stopped but tx_dma_busy is not handled.

Rework the driver by using two new functions to solve this issue:
- stm32_usart_tx_dma_started return true if DMA TX have a descriptor.
- stm32_usart_tx_dma_enabled return true if DMAT bit is set.

stm32_usart_tx_dma_started uses tx_dma_busy flag to prevent dual DMA
transaction at the same time. This flag is set when a DMA transaction
begins and is unset when dmaengine_terminate_async function is called.
A new DMA transaction cannot be created if this flag is set.

Create a new function "stm32_usart_tx_dma_terminate" to be sure the flag
is unset after each call of dmaengine_terminate_async.

Signed-off-by: default avatarErwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: default avatarValentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20220104182445.4195-3-valentin.caron@foss.st.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 56a23f93

drivers/tty/serial/stm32-usart.c

+48 −18
Original line number Diff line number Diff line
@@ -365,6 +365,31 @@ static unsigned int stm32_usart_receive_chars(struct uart_port *port, bool force 
	return size;

}



static void stm32_usart_tx_dma_terminate(struct stm32_port *stm32_port)

{

	dmaengine_terminate_async(stm32_port->tx_ch);

	stm32_port->tx_dma_busy = false;

}



static bool stm32_usart_tx_dma_started(struct stm32_port *stm32_port)

{

	/*

	 * We cannot use the function "dmaengine_tx_status" to know the

	 * status of DMA. This function does not show if the "dma complete"

	 * callback of the DMA transaction has been called. So we prefer

	 * to use "tx_dma_busy" flag to prevent dual DMA transaction at the

	 * same time.

	 */

	return stm32_port->tx_dma_busy;

}



static bool stm32_usart_tx_dma_enabled(struct stm32_port *stm32_port)

{

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



	return !!(readl_relaxed(stm32_port->port.membase + ofs->cr3) & USART_CR3_DMAT);

}



static void stm32_usart_tx_dma_complete(void *arg)

{

	struct uart_port *port = arg;
@@ -372,9 +397,8 @@ static void stm32_usart_tx_dma_complete(void *arg) 
	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;

	unsigned long flags;



	dmaengine_terminate_async(stm32port->tx_ch);

	stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

	stm32port->tx_dma_busy = false;

	stm32_usart_tx_dma_terminate(stm32port);



	/* Let's see if we have pending data to send */

	spin_lock_irqsave(&port->lock, flags);
@@ -428,10 +452,8 @@ static void stm32_usart_transmit_chars_pio(struct uart_port *port) 
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;

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



	if (stm32_port->tx_dma_busy) {

	if (stm32_usart_tx_dma_enabled(stm32_port))

		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

		stm32_port->tx_dma_busy = false;

	}



	while (!uart_circ_empty(xmit)) {

		/* Check that TDR is empty before filling FIFO */
@@ -457,10 +479,11 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port) 
	struct dma_async_tx_descriptor *desc = NULL;

	unsigned int count, i;



	if (stm32port->tx_dma_busy)

	if (stm32_usart_tx_dma_started(stm32port)) {

		if (!stm32_usart_tx_dma_enabled(stm32port))

			stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);

		return;



	stm32port->tx_dma_busy = true;

	}



	count = uart_circ_chars_pending(xmit);
@@ -491,13 +514,21 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port) 
	if (!desc)

		goto fallback_err;



	/*

	 * Set "tx_dma_busy" flag. This flag will be released when

	 * dmaengine_terminate_async will be called. This flag helps

	 * transmit_chars_dma not to start another DMA transaction

	 * if the callback of the previous is not yet called.

	 */

	stm32port->tx_dma_busy = true;



	desc->callback = stm32_usart_tx_dma_complete;

	desc->callback_param = port;



	/* Push current DMA TX transaction in the pending queue */

	if (dma_submit_error(dmaengine_submit(desc))) {

		/* dma no yet started, safe to free resources */

		dmaengine_terminate_async(stm32port->tx_ch);

		stm32_usart_tx_dma_terminate(stm32port);

		goto fallback_err;

	}
@@ -522,12 +553,13 @@ static void stm32_usart_transmit_chars(struct uart_port *port) 
	struct circ_buf *xmit = &port->state->xmit;



	if (port->x_char) {

		if (stm32_port->tx_dma_busy)

		if (stm32_usart_tx_dma_started(stm32_port) &&

		    stm32_usart_tx_dma_enabled(stm32_port))

			stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

		writel_relaxed(port->x_char, port->membase + ofs->tdr);

		port->x_char = 0;

		port->icount.tx++;

		if (stm32_port->tx_dma_busy)

		if (stm32_usart_tx_dma_started(stm32_port))

			stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);

		return;

	}
@@ -719,9 +751,8 @@ static void stm32_usart_flush_buffer(struct uart_port *port) 
	const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;



	if (stm32_port->tx_ch) {

		dmaengine_terminate_async(stm32_port->tx_ch);

		stm32_usart_tx_dma_terminate(stm32_port);

		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

		stm32_port->tx_dma_busy = false;

	}

}
@@ -883,10 +914,11 @@ static void stm32_usart_shutdown(struct uart_port *port) 
	u32 val, isr;

	int ret;



	if (stm32_port->tx_dma_busy) {

		dmaengine_terminate_async(stm32_port->tx_ch);

	if (stm32_usart_tx_dma_enabled(stm32_port))

		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);

	}



	if (stm32_usart_tx_dma_started(stm32_port))

		stm32_usart_tx_dma_terminate(stm32_port);



	/* Disable modem control interrupts */

	stm32_usart_disable_ms(port);
@@ -1424,8 +1456,6 @@ static int stm32_usart_of_dma_tx_probe(struct stm32_port *stm32port, 
	struct dma_slave_config config;

	int ret;



	stm32port->tx_dma_busy = false;



	stm32port->tx_buf = dma_alloc_coherent(dev, TX_BUF_L,

					       &stm32port->tx_dma_buf,

					       GFP_KERNEL);

drivers/tty/serial/stm32-usart.h

+1 −1
Original line number Diff line number Diff line
@@ -264,7 +264,7 @@ struct stm32_port { 
	u32 cr1_irq;		 /* USART_CR1_RXNEIE or RTOIE */

	u32 cr3_irq;		 /* USART_CR3_RXFTIE */

	int last_res;

	bool tx_dma_busy;	 /* dma tx busy               */

	bool tx_dma_busy;	 /* dma tx transaction in progress */

	bool throttled;		 /* port throttled            */

	bool hw_flow_control;

	bool swap;		 /* swap RX & TX pins */