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: Erwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20220104182445.4195-3-valentin.caron@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 6cfc3be..52755a5 100644 (file)
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -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);

diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index e23916b..feab952 100644 (file)
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -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 */