[PATCH v4 09/14] mmc: omap_hsmmc: set max_segs based on dma engine limitations

[Matt Porter]

The EDMA DMAC has a hardware limitation that prevents supporting
scatter gather lists with any number of segments. The DMA Engine
API reports the maximum number of segments a channel can support
via the optional dma_get_channel_caps() API. If the nr_segs
capability is present, the value is used to configure mmc->max_segs
appropriately.

Signed-off-by: Matt Porter <mporter at ti.com>
---
 drivers/mmc/host/omap_hsmmc.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index e79b12d..f74bd69 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -1769,6 +1769,7 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
 	const struct of_device_id *match;
 	dma_cap_mask_t mask;
 	unsigned tx_req, rx_req;
+	struct dmaengine_chan_caps *dma_chan_caps;
 	struct pinctrl *pinctrl;
 
 	match = of_match_device(of_match_ptr(omap_mmc_of_match), &pdev->dev);
@@ -1935,6 +1936,11 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
 		goto err_irq;
 	}
 
+	/* Some DMA Engines only handle a limited number of SG segments */
+	dma_chan_caps = dma_get_channel_caps(host->rx_chan, DMA_DEV_TO_MEM);
+	if (dma_chan_caps && dma_chan_caps->seg_nr)
+		mmc->max_segs = dma_chan_caps->seg_nr;
+
 	/* Request IRQ for MMC operations */
 	ret = request_irq(host->irq, omap_hsmmc_irq, 0,
 			mmc_hostname(mmc), host);
-- 
1.7.9.5