serial: fsl_lpuart: add sysrq support when using dma

Add handling of magic sysrq keys when using dma/edma.

Tested by sending BREAK followed by a sysrq command inside
a 5 secs time window, by:

echo 1 > /proc/sys/kernel/sysrq

BREAK + h, t, e, b, c

Tested also sending a command after 5 secs after BREAK, that's
properly ignored.

Signed-off-by: Angelo Dureghello <angelo.dureghello@timesys.com>
Link: https://lore.kernel.org/r/20201004161144.1307174-1-angelo.dureghello@timesys.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 590c901a1fc52a3f26e4c464a3ffb7268748cb97..ff4b88c637d0e3021077add0632b34f8029efce8 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -976,6 +976,15 @@ static irqreturn_t lpuart_int(int irq, void *dev_id)
 
        sts = readb(sport->port.membase + UARTSR1);
 
+       /* SysRq, using dma, check for linebreak by framing err. */
+       if (sts & UARTSR1_FE && sport->lpuart_dma_rx_use) {
+               readb(sport->port.membase + UARTDR);
+               uart_handle_break(&sport->port);
+               /* linebreak produces some garbage, removing it */
+               writeb(UARTCFIFO_RXFLUSH, sport->port.membase + UARTCFIFO);
+               return IRQ_HANDLED;
+       }
+
        if (sts & UARTSR1_RDRF && !sport->lpuart_dma_rx_use)
                lpuart_rxint(sport);
 
@@ -1004,6 +1013,37 @@ static irqreturn_t lpuart32_int(int irq, void *dev_id)
        return IRQ_HANDLED;
 }
 
+
+static inline void lpuart_handle_sysrq_chars(struct uart_port *port,
+                                            unsigned char *p, int count)
+{
+       while (count--) {
+               if (*p && uart_handle_sysrq_char(port, *p))
+                       return;
+               p++;
+       }
+}
+
+static void lpuart_handle_sysrq(struct lpuart_port *sport)
+{
+       struct circ_buf *ring = &sport->rx_ring;
+       int count;
+
+       if (ring->head < ring->tail) {
+               count = sport->rx_sgl.length - ring->tail;
+               lpuart_handle_sysrq_chars(&sport->port,
+                                         ring->buf + ring->tail, count);
+               ring->tail = 0;
+       }
+
+       if (ring->head > ring->tail) {
+               count = ring->head - ring->tail;
+               lpuart_handle_sysrq_chars(&sport->port,
+                                         ring->buf + ring->tail, count);
+               ring->tail = ring->head;
+       }
+}
+
 static void lpuart_copy_rx_to_tty(struct lpuart_port *sport)
 {
        struct tty_port *port = &sport->port.state->port;
@@ -1090,6 +1130,15 @@ static void lpuart_copy_rx_to_tty(struct lpuart_port *sport)
         */
        ring->head = sport->rx_sgl.length - state.residue;
        BUG_ON(ring->head > sport->rx_sgl.length);
+
+       /*
+        * Silent handling of keys pressed in the sysrq timeframe
+        */
+       if (sport->port.sysrq) {
+               lpuart_handle_sysrq(sport);
+               goto exit;
+       }
+
        /*
         * At this point ring->head may point to the first byte right after the
         * last byte of the dma buffer:
@@ -1121,6 +1170,7 @@ static void lpuart_copy_rx_to_tty(struct lpuart_port *sport)
                sport->port.icount.rx += count;
        }
 
+exit:
        dma_sync_sg_for_device(chan->device->dev, &sport->rx_sgl, 1,
                               DMA_FROM_DEVICE);
 
@@ -1557,6 +1607,7 @@ err:
 static void lpuart_rx_dma_startup(struct lpuart_port *sport)
 {
        int ret;
+       unsigned char cr3;
 
        if (!sport->dma_rx_chan)
                goto err;
@@ -1573,6 +1624,12 @@ static void lpuart_rx_dma_startup(struct lpuart_port *sport)
        sport->lpuart_dma_rx_use = true;
        rx_dma_timer_init(sport);
 
+       if (sport->port.has_sysrq) {
+               cr3 = readb(sport->port.membase + UARTCR3);
+               cr3 |= UARTCR3_FEIE;
+               writeb(cr3, sport->port.membase + UARTCR3);
+       }
+
        return;
 
 err: