OMAP3: McBSP: Change the way how the FIFO is handled

Use the actual FIFO size in words as buffer_size on OMAP3.
Change the threshold configuration to use 1 based numbering, when
specifying the allowed threshold maximum or the McBSP threshold value.
Set the default maximum threshold to (buffer_size - 0x10) intialy.
>From users of McBSP, now it is expected to use this method.
Asking for threshold 1 means that the value written to threshold registers
are going to be 0, which means 1 word threshold.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Acked-by: Jarkko Nikula <jhnikula@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolsfonmicro.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>

1 files changed, 20 insertions, 10 deletions

diff --git a/arch/arm/plat-omap/mcbsp.c b/arch/arm/plat-omap/mcbsp.c
index 8bab0b2..4ef4604 100644
--- a/arch/arm/plat-omap/mcbsp.c
+++ b/arch/arm/plat-omap/mcbsp.c
@@ -481,9 +481,9 @@ int omap_st_is_enabled(unsigned int id)
 EXPORT_SYMBOL(omap_st_is_enabled);
 
 /*
- * omap_mcbsp_set_tx_threshold configures how to deal
- * with transmit threshold. the threshold value and handler can be
- * configure in here.
+ * omap_mcbsp_set_rx_threshold configures the transmit threshold in words.
+ * The threshold parameter is 1 based, and it is converted (threshold - 1)
+ * for the THRSH2 register.
  */
 void omap_mcbsp_set_tx_threshold(unsigned int id, u16 threshold)
 {
@@ -498,14 +498,15 @@ void omap_mcbsp_set_tx_threshold(unsigned int id, u16 threshold)
 	}
 	mcbsp = id_to_mcbsp_ptr(id);
 
-	MCBSP_WRITE(mcbsp, THRSH2, threshold);
+	if (threshold && threshold <= mcbsp->max_tx_thres)
+		MCBSP_WRITE(mcbsp, THRSH2, threshold - 1);
 }
 EXPORT_SYMBOL(omap_mcbsp_set_tx_threshold);
 
 /*
- * omap_mcbsp_set_rx_threshold configures how to deal
- * with receive threshold. the threshold value and handler can be
- * configure in here.
+ * omap_mcbsp_set_rx_threshold configures the receive threshold in words.
+ * The threshold parameter is 1 based, and it is converted (threshold - 1)
+ * for the THRSH1 register.
  */
 void omap_mcbsp_set_rx_threshold(unsigned int id, u16 threshold)
 {
@@ -520,7 +521,8 @@ void omap_mcbsp_set_rx_threshold(unsigned int id, u16 threshold)
 	}
 	mcbsp = id_to_mcbsp_ptr(id);
 
-	MCBSP_WRITE(mcbsp, THRSH1, threshold);
+	if (threshold && threshold <= mcbsp->max_rx_thres)
+		MCBSP_WRITE(mcbsp, THRSH1, threshold - 1);
 }
 EXPORT_SYMBOL(omap_mcbsp_set_rx_threshold);
 
@@ -1697,8 +1699,16 @@ static inline void __devinit omap34xx_device_init(struct omap_mcbsp *mcbsp)
 {
 	mcbsp->dma_op_mode = MCBSP_DMA_MODE_ELEMENT;
 	if (cpu_is_omap34xx()) {
-		mcbsp->max_tx_thres = max_thres(mcbsp);
-		mcbsp->max_rx_thres = max_thres(mcbsp);
+		/*
+		 * Initially configure the maximum thresholds to a safe value.
+		 * The McBSP FIFO usage with these values should not go under
+		 * 16 locations.
+		 * If the whole FIFO without safety buffer is used, than there
+		 * is a possibility that the DMA will be not able to push the
+		 * new data on time, causing channel shifts in runtime.
+		 */
+		mcbsp->max_tx_thres = max_thres(mcbsp) - 0x10;
+		mcbsp->max_rx_thres = max_thres(mcbsp) - 0x10;
 		/*
 		 * REVISIT: Set dmap_op_mode to THRESHOLD as default
 		 * for mcbsp2 instances.