hsu: add a periodic timer to check dma rx channel

A general problem for uart rx dma channel is you never know when
and how much data will be received, so usually preset it a DMA
descriptor with a big size, and rely on DMA RX timeout IRQ to
know there is some data in rx channel.

For a RX data size of multiple of MOTSR, there will be no timeout
IRQ issued, thus OS will never be notified about that.

This is a work around for that, current timer frequency is 5 times
per second, it should vary according to the baud rate

When future silicon version fix the problem, this workaround need
be removed

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 47 insertions, 3 deletions

diff --git a/drivers/serial/mfd.c b/drivers/serial/mfd.c
index 300dcb134e07..ed2bf6b14a4a 100644
--- a/drivers/serial/mfd.c
+++ b/drivers/serial/mfd.c
@@ -64,6 +64,8 @@
 #define mfd_readl(obj, offset)          readl(obj->reg + offset)
 #define mfd_writel(obj, offset, val)    writel(val, obj->reg + offset)
 
+#define HSU_DMA_TIMEOUT_CHECK_FREQ      (HZ/10)
+
 struct hsu_dma_buffer {
         u8              *buf;
         dma_addr_t      dma_addr;
@@ -75,7 +77,8 @@ struct hsu_dma_chan {
         u32     id;
         u32     dirt;   /* to or from device */
         struct uart_hsu_port    *uport;
-        void __iomem    *reg;
+        void __iomem            *reg;
+        struct timer_list       rx_timer; /* only needed by RX channel */
 };
 
 struct uart_hsu_port {
@@ -377,6 +380,8 @@ void hsu_dma_start_rx_chan(struct hsu_dma_chan *rxc, struct hsu_dma_buffer *dbuf
                                          | (0x1 << 24)  /* timeout bit, see HSU Errata 1 */
                                          );
         chan_writel(rxc, HSU_CH_CR, 0x3);
+
+        mod_timer(&rxc->rx_timer, jiffies + HSU_DMA_TIMEOUT_CHECK_FREQ);
 }
 
 /* Protected by spin_lock_irqsave(port->lock) */
@@ -437,8 +442,13 @@ void hsu_dma_rx(struct uart_hsu_port *up, u32 int_sts)
         /* We can use 2 ways to calc the actual transfer len */
         count = chan_readl(chan, HSU_CH_D0SAR) - dbuf->dma_addr;
 
-        if (!count)
+        if (!count) {
+                /* restart the channel before we leave */
+                chan_writel(chan, HSU_CH_CR, 0x3);
                 return;
+        }
+
+        del_timer(&chan->rx_timer);
 
         dma_sync_single_for_cpu(port->dev, dbuf->dma_addr,
                         dbuf->dma_size, DMA_FROM_DEVICE);
@@ -463,9 +473,12 @@ void hsu_dma_rx(struct uart_hsu_port *up, u32 int_sts)
                                          | (0x1 << 16)
                                          | (0x1 << 24)  /* timeout bit, see HSU Errata 1 */
                                          );
+        tty_flip_buffer_push(tty);
+
         chan_writel(chan, HSU_CH_CR, 0x3);
+        chan->rx_timer.expires = jiffies + HSU_DMA_TIMEOUT_CHECK_FREQ;
+        add_timer(&chan->rx_timer);
 
-        tty_flip_buffer_push(tty);
 }
 
 static void serial_hsu_stop_rx(struct uart_port *port)
@@ -893,6 +906,8 @@ static void serial_hsu_shutdown(struct uart_port *port)
                 container_of(port, struct uart_hsu_port, port);
         unsigned long flags;
 
+        del_timer_sync(&up->rxc->rx_timer);
+
         /* Disable interrupts from this port */
         up->ier = 0;
         serial_out(up, UART_IER, 0);
@@ -1348,6 +1363,28 @@ err_disable:
         return ret;
 }
 
+static void hsu_dma_rx_timeout(unsigned long data)
+{
+        struct hsu_dma_chan *chan = (void *)data;
+        struct uart_hsu_port *up = chan->uport;
+        struct hsu_dma_buffer *dbuf = &up->rxbuf;
+        int count = 0;
+        unsigned long flags;
+
+        spin_lock_irqsave(&up->port.lock, flags);
+
+        count = chan_readl(chan, HSU_CH_D0SAR) - dbuf->dma_addr;
+
+        if (!count) {
+                mod_timer(&chan->rx_timer, jiffies + HSU_DMA_TIMEOUT_CHECK_FREQ);
+                goto exit;
+        }
+
+        hsu_dma_rx(up, 0);
+exit:
+        spin_unlock_irqrestore(&up->port.lock, flags);
+}
+
 static void hsu_global_init(void)
 {
         struct hsu_port *hsu;
@@ -1409,6 +1446,13 @@ static void hsu_global_init(void)
                 dchan->uport = &hsu->port[i/2];
                 dchan->reg = hsu->reg + HSU_DMA_CHANS_REG_OFFSET +
                                 i * HSU_DMA_CHANS_REG_LENGTH;
+
+                /* Work around for RX */
+                if (dchan->dirt == DMA_FROM_DEVICE) {
+                        init_timer(&dchan->rx_timer);
+                        dchan->rx_timer.function = hsu_dma_rx_timeout;
+                        dchan->rx_timer.data = (unsigned long)dchan;
+                }
                 dchan++;
         }