svn commit: r354846 - head/sys/arm/broadcom/bcm2835

[Kyle Evans]

Author: kevans
Date: Tue Nov 19 04:23:57 2019
New Revision: 354846
URL: https://svnweb.freebsd.org/changeset/base/354846

Log:
  bcm2835_sdhci: formalize DMA tag/segment scaling requirements
  
  This allows easy and care-free scaling of NUM_DMA_SEGS with proper-ish
  calculations to make sure we can actually handle the number of segments we'd
  like to handle on average so that performance comparisons can be easily made
  at different values if/once we can actually handle it. It also makes it
  helps the untrained reader understand more quickly the reasoning behind the
  choice of maxsize/maxsegs/maxsegsize.

Modified:
  head/sys/arm/broadcom/bcm2835/bcm2835_sdhci.c

Modified: head/sys/arm/broadcom/bcm2835/bcm2835_sdhci.c
==============================================================================
--- head/sys/arm/broadcom/bcm2835/bcm2835_sdhci.c	Tue Nov 19 03:45:41 2019	(r354845)
+++ head/sys/arm/broadcom/bcm2835/bcm2835_sdhci.c	Tue Nov 19 04:23:57 2019	(r354846)
@@ -66,7 +66,17 @@ __FBSDID("$FreeBSD$");
 #define	BCM2838_DEFAULT_SDHCI_FREQ	100
 
 #define	BCM_SDHCI_BUFFER_SIZE		512
-#define	NUM_DMA_SEGS			2
+/*
+ * NUM_DMA_SEGS is the number of DMA segments we want to accommodate on average.
+ * We add in a number of segments based on how much we may need to spill into
+ * another segment due to crossing page boundaries.  e.g. up to PAGE_SIZE, an
+ * extra page is needed as we can cross a page boundary exactly once.
+ */
+#define	NUM_DMA_SEGS			1
+#define	NUM_DMA_SPILL_SEGS		\
+	((((NUM_DMA_SEGS * BCM_SDHCI_BUFFER_SIZE) - 1) / PAGE_SIZE) + 1)
+#define	ALLOCATED_DMA_SEGS		(NUM_DMA_SEGS +	NUM_DMA_SPILL_SEGS)
+#define	BCM_DMA_MAXSIZE			(NUM_DMA_SEGS * BCM_SDHCI_BUFFER_SIZE)
 
 #define	DATA_PENDING_MASK	(SDHCI_INT_DATA_AVAIL | SDHCI_INT_SPACE_AVAIL)
 
@@ -141,8 +151,8 @@ struct bcm_sdhci_softc {
 	bus_dma_tag_t		sc_dma_tag;
 	bus_dmamap_t		sc_dma_map;
 	vm_paddr_t		sc_sdhci_buffer_phys;
-	bus_addr_t		dmamap_seg_addrs[NUM_DMA_SEGS];
-	bus_size_t		dmamap_seg_sizes[NUM_DMA_SEGS];
+	bus_addr_t		dmamap_seg_addrs[ALLOCATED_DMA_SEGS];
+	bus_size_t		dmamap_seg_sizes[ALLOCATED_DMA_SEGS];
 	int			dmamap_seg_count;
 	int			dmamap_seg_index;
 	int			dmamap_status;
@@ -314,7 +324,7 @@ bcm_sdhci_attach(device_t dev)
 		err = bus_dma_tag_create(bus_get_dma_tag(dev),
 		    1, 0, BUS_SPACE_MAXADDR_32BIT,
 		    BUS_SPACE_MAXADDR, NULL, NULL,
-		    BCM_SDHCI_BUFFER_SIZE, NUM_DMA_SEGS, BCM_SDHCI_BUFFER_SIZE,
+		    BCM_DMA_MAXSIZE, ALLOCATED_DMA_SEGS, BCM_SDHCI_BUFFER_SIZE,
 		    BUS_DMA_ALLOCNOW, NULL, NULL,
 		    &sc->sc_dma_tag);