Documented the value written for R300_TX_CNTL cache flush.

src/mesa/drivers/dri/r300/r300_cmdbuf.c

@@ -174,11 +174,12 @@ static __inline__ void r300DoEmitState(r300ContextPtr r300, GLboolean dirty)
 	dest ++;
 	r300->cmdbuf.count_used ++;
 
+	/* Emit cache flush */
 	*dest = cmdpacket0(R300_TX_CNTL, 1);
 	dest ++;
 	r300->cmdbuf.count_used ++;
 	
-	*dest = 0x0;
+	*dest = R300_TX_FLUSH;
 	dest ++;
 	r300->cmdbuf.count_used ++;
 	

src/mesa/drivers/dri/r300/r300_reg.h

@@ -497,6 +497,7 @@ USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 /* Zero to flush caches. */
 #define R300_TX_CNTL                        0x4100
+#define R300_TX_FLUSH                       0x0
 
 /* The upper enable bits are guessed, based on fglrx reported limits. */
 #define R300_TX_ENABLE                      0x4104