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bcm2835_sdhci: formalize DMA tag/segment scaling requirements

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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.
This commit is contained in:
Kyle Evans 2019-11-19 04:23:57 +00:00
parent ddf5b0fb84
commit 55fa224bd1
1 changed files with 14 additions and 4 deletions
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18
sys/arm/broadcom/bcm2835/bcm2835_sdhci.c
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@ -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);