svn commit: r247092 - head/sys/dev/ath/ath_hal/ar5416

[Adrian Chadd]

Author: adrian
Date: Thu Feb 21 08:42:40 2013
New Revision: 247092
URL: http://svnweb.freebsd.org/changeset/base/247092

Log:
  Be slightly more paranoid with the TX DMA buffer maximum threshold.
  
  Specifically - never jack the TX FIFO threshold up to the absolute
  maximum; always leave enough space for two DMA transactions to
  appear.
  
  This is a paranoia from the Linux ath9k driver.  It can't hurt.
  
  Obtained from:	Linux ath9k

Modified:
  head/sys/dev/ath/ath_hal/ar5416/ar5416_attach.c
  head/sys/dev/ath/ath_hal/ar5416/ar5416_reset.c

Modified: head/sys/dev/ath/ath_hal/ar5416/ar5416_attach.c
==============================================================================
--- head/sys/dev/ath/ath_hal/ar5416/ar5416_attach.c	Thu Feb 21 08:21:14 2013	(r247091)
+++ head/sys/dev/ath/ath_hal/ar5416/ar5416_attach.c	Thu Feb 21 08:42:40 2013	(r247092)
@@ -244,9 +244,23 @@ ar5416InitState(struct ath_hal_5416 *ahp
 	/* Set overridable ANI methods */
 	AH5212(ah)->ah_aniControl = ar5416AniControl;
 
-	/* Default FIFO Trigger levels */
+	/*
+	 * Default FIFO Trigger levels
+	 *
+	 * These define how filled the TX FIFO needs to be before
+	 * the baseband begins to be given some data.
+	 *
+	 * To be paranoid, we ensure that the TX trigger level always
+	 * has at least enough space for two TX DMA to occur.
+	 * The TX DMA size is currently hard-coded to AR_TXCFG_DMASZ_128B.
+	 * That means we need to leave at least 256 bytes available in
+	 * the TX DMA FIFO.
+	 */
 #define	AR_FTRIG_512B	0x00000080 // 5 bits total
-	/* AR9285/AR9271 need to use half the TX FIFOs */
+	/*
+	 * AR9285/AR9271 have half the size TX FIFO compared to
+	 * other devices
+	 */
 	if (AR_SREV_KITE(ah) || AR_SREV_9271(ah)) {
 		AH5212(ah)->ah_txTrigLev = (AR_FTRIG_256B >> AR_FTRIG_S);
 		AH5212(ah)->ah_maxTxTrigLev = ((2048 / 64) - 1);
@@ -255,6 +269,9 @@ ar5416InitState(struct ath_hal_5416 *ahp
 		AH5212(ah)->ah_maxTxTrigLev = ((4096 / 64) - 1);
 	}
 #undef	AR_FTRIG_512B
+
+	/* And now leave some headspace - 256 bytes */
+	AH5212(ah)->ah_maxTxTrigLev -= 4;
 }
 
 uint32_t

Modified: head/sys/dev/ath/ath_hal/ar5416/ar5416_reset.c
==============================================================================
--- head/sys/dev/ath/ath_hal/ar5416/ar5416_reset.c	Thu Feb 21 08:21:14 2013	(r247091)
+++ head/sys/dev/ath/ath_hal/ar5416/ar5416_reset.c	Thu Feb 21 08:42:40 2013	(r247092)
@@ -570,6 +570,10 @@ ar5416InitDMA(struct ath_hal *ah)
 	/*
 	 * let mac dma writes be in 128 byte chunks
 	 */
+	/*
+	 * XXX If you change this, you must change the headroom
+	 * assigned in ah_maxTxTrigLev - see ar5416InitState().
+	 */
 	OS_REG_WRITE(ah, AR_RXCFG, 
 		(OS_REG_READ(ah, AR_RXCFG) & ~AR_RXCFG_DMASZ_MASK) | AR_RXCFG_DMASZ_128B);