lantiq: atm: Use a tasklet to handle incoming packets. Fix #12917.

Incoming packets are now processes in a tasklet instead of in the
irq handler; this should improve latency.

This patch is based on a previous version of ltq-atm driver, which
did implement a tasklet.

It has been tested on a arv4518pw with a
Lantiq Danube for about a month and it seems to work well.

Signed-off-by: Luca Dariz <luca.dariz@gmail.com>
Tested-by: Luca Dariz <luca.dariz@gmail.com>

SVN-Revision: 36902

package/platform/lantiq/ltq-atm/src/ltq_atm.c

@@ -199,6 +199,8 @@ static inline void mailbox_oam_rx_handler(void);
 static inline void mailbox_aal_rx_handler(void);
 static irqreturn_t mailbox_irq_handler(int, void *);
 static inline void mailbox_signal(unsigned int, int);
+static void do_ppe_tasklet(unsigned long);
+DECLARE_TASKLET(g_dma_tasklet, do_ppe_tasklet, 0);
 
 /*
  *  QSB & HTU setting functions
@@ -491,6 +493,9 @@ static void ppe_close(struct atm_vcc *vcc)
 		break;
 	}
 
+	/* wait for incoming packets to be processed by upper layers */
+	tasklet_unlock_wait(&g_dma_tasklet);
+
 PPE_CLOSE_EXIT:
 	return;
 }
@@ -1039,14 +1044,25 @@ static inline void mailbox_aal_rx_handler(void)
 	}
 }
 
+static void do_ppe_tasklet(unsigned long data)
+{
+	*MBOX_IGU1_ISRC = *MBOX_IGU1_ISR;
+	mailbox_oam_rx_handler();
+	mailbox_aal_rx_handler();
+
+	if ((*MBOX_IGU1_ISR & ((1 << RX_DMA_CH_AAL) | (1 << RX_DMA_CH_OAM))) != 0)
+		tasklet_schedule(&g_dma_tasklet);
+	else
+		enable_irq(PPE_MAILBOX_IGU1_INT);
+}
+
 static irqreturn_t mailbox_irq_handler(int irq, void *dev_id)
 {
 	if ( !*MBOX_IGU1_ISR )
 		return IRQ_HANDLED;
 
-	*MBOX_IGU1_ISRC = *MBOX_IGU1_ISR;
-	mailbox_oam_rx_handler();
-	mailbox_aal_rx_handler();
+	disable_irq_nosync(PPE_MAILBOX_IGU1_INT);
+	tasklet_schedule(&g_dma_tasklet);
 
 	return IRQ_HANDLED;
 }