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Message-ID: <20230803130134.155355-2-valentin.caron@foss.st.com>
Date: Thu, 3 Aug 2023 15:01:29 +0200
From: Valentin Caron <valentin.caron@...s.st.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Jiri Slaby <jirislaby@...nel.org>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
Amelie Delaunay <amelie.delaunay@...s.st.com>,
<linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-stm32@...md-mailman.stormreply.com>,
<linux-arm-kernel@...ts.infradead.org>,
Valentin Caron <valentin.caron@...s.st.com>
Subject: [PATCH 1/6] serial: stm32: avoid clearing DMAT bit during transfer
It's rather advised to rely on DMA pause / resume instead of
clearing/setting DMA request enable bit for the same purpose. Some DMA
request/acknowledge race may encountered by doing so. We prefer to use
dmaengine_pause and resume instead to pause a dma transfer when it is
necessary.
It is also safer to close DMA before reset DMAT in stm32_usart_shutdown.
Signed-off-by: Valentin Caron <valentin.caron@...s.st.com>
---
drivers/tty/serial/stm32-usart.c | 76 ++++++++++++++++++--------------
1 file changed, 44 insertions(+), 32 deletions(-)
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index be47cd343cf6..2f9672ba4ed3 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -506,13 +506,6 @@ static bool stm32_usart_tx_dma_started(struct stm32_port *stm32_port)
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;
@@ -591,9 +584,6 @@ 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_usart_tx_dma_enabled(stm32_port))
- stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
-
while (!uart_circ_empty(xmit)) {
/* Check that TDR is empty before filling FIFO */
if (!(readl_relaxed(port->membase + ofs->isr) & USART_SR_TXE))
@@ -616,10 +606,16 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port)
struct circ_buf *xmit = &port->state->xmit;
struct dma_async_tx_descriptor *desc = NULL;
unsigned int count;
+ int ret;
if (stm32_usart_tx_dma_started(stm32port)) {
- if (!stm32_usart_tx_dma_enabled(stm32port))
- stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);
+ if (dmaengine_tx_status(stm32port->tx_ch,
+ stm32port->tx_ch->cookie,
+ NULL) == DMA_PAUSED) {
+ ret = dmaengine_resume(stm32port->tx_ch);
+ if (ret < 0)
+ goto dma_err;
+ }
return;
}
@@ -664,11 +660,9 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port)
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 */
- stm32_usart_tx_dma_terminate(stm32port);
- goto fallback_err;
- }
+ /* DMA no yet started, safe to free resources */
+ if (dma_submit_error(dmaengine_submit(desc)))
+ goto dma_err;
/* Issue pending DMA TX requests */
dma_async_issue_pending(stm32port->tx_ch);
@@ -679,6 +673,10 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port)
return;
+dma_err:
+ dev_err(port->dev, "DMA failed with error code: %d\n", ret);
+ stm32_usart_tx_dma_terminate(stm32port);
+
fallback_err:
stm32_usart_transmit_chars_pio(port);
}
@@ -701,9 +699,15 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
if (port->x_char) {
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);
-
+ dmaengine_tx_status(stm32_port->tx_ch,
+ stm32_port->tx_ch->cookie,
+ NULL) == DMA_IN_PROGRESS) {
+ ret = dmaengine_pause(stm32_port->tx_ch);
+ if (ret < 0) {
+ dev_err(port->dev, "DMA failed with error code: %d\n", ret);
+ stm32_usart_tx_dma_terminate(stm32_port);
+ }
+ }
/* Check that TDR is empty before filling FIFO */
ret =
readl_relaxed_poll_timeout_atomic(port->membase + ofs->isr,
@@ -716,8 +720,14 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
writel_relaxed(port->x_char, port->membase + ofs->tdr);
port->x_char = 0;
port->icount.tx++;
- if (stm32_usart_tx_dma_started(stm32_port))
- stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);
+
+ if (stm32_usart_tx_dma_started(stm32_port)) {
+ ret = dmaengine_resume(stm32_port->tx_ch);
+ if (ret < 0) {
+ dev_err(port->dev, "DMA failed with error code: %d\n", ret);
+ stm32_usart_tx_dma_terminate(stm32_port);
+ }
+ }
return;
}
@@ -850,11 +860,16 @@ static void stm32_usart_disable_ms(struct uart_port *port)
static void stm32_usart_stop_tx(struct uart_port *port)
{
struct stm32_port *stm32_port = to_stm32_port(port);
- const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+ int ret;
stm32_usart_tx_interrupt_disable(port);
- 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);
+ if (stm32_usart_tx_dma_started(stm32_port)) {
+ ret = dmaengine_pause(stm32_port->tx_ch);
+ if (ret < 0) {
+ dev_err(port->dev, "DMA failed with error code: %d\n", ret);
+ stm32_usart_tx_dma_terminate(stm32_port);
+ }
+ }
stm32_usart_rs485_rts_disable(port);
}
@@ -878,12 +893,9 @@ static void stm32_usart_start_tx(struct uart_port *port)
static void stm32_usart_flush_buffer(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->tx_ch) {
+ if (stm32_port->tx_ch)
stm32_usart_tx_dma_terminate(stm32_port);
- stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
- }
}
/* Throttle the remote when input buffer is about to overflow. */
@@ -1042,12 +1054,12 @@ static void stm32_usart_shutdown(struct uart_port *port)
u32 val, isr;
int ret;
- 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);
+ if (stm32_port->tx_ch)
+ stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
+
/* Disable modem control interrupts */
stm32_usart_disable_ms(port);
--
2.25.1
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