Subject: [PATCH mmc-next 3/3] mmc: sdhci-of-dwcmshc: solve 128MB DMA boundary limitation

From: [email-masked] (Jisheng Zhang)
Date: Wed, 25 Jul 2018 17:47:49 +0800

When using DMA, if the DMA addr spans 128MB boundary, we have to split
the DMA transfer into two so that each one doesn't exceed the boundary.

Signed-off-by: Jisheng Zhang <[email-masked]>
---
 drivers/mmc/host/sdhci-of-dwcmshc.c | 41 +++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-of-dwcmshc.c
index 1b7cd144fb01..01b5cb772554 100644
--- a/drivers/mmc/host/sdhci-of-dwcmshc.c
+++ b/drivers/mmc/host/sdhci-of-dwcmshc.c
@@ -13,16 +13,45 @@
 
 #include "sdhci-pltfm.h"
 
+#define BOUNDARY_OK(addr, len) \
+	((addr | (SZ_128M - 1)) == ((addr + len) | (SZ_128M - 1)))
+
 struct dwcmshc_priv {
 	struct clk	*bus_clk;
 };
 
+/*
+ * if DMA addr spans 128MB boundary, we split the DMA transfer into two
+ * so that the DMA transfer doesn't exceed the boundary.
+ */
+static unsigned int dwcmshc_adma_write_desc(struct sdhci_host *host,
+					    void *desc, dma_addr_t addr,
+					    int len, unsigned int cmd)
+{
+	int tmplen, offset;
+
+	if (BOUNDARY_OK(addr, len))
+		return _sdhci_adma_write_desc(host, desc, addr, len, cmd);
+
+	offset = addr & (SZ_128M - 1);
+	tmplen = SZ_128M - offset;
+	_sdhci_adma_write_desc(host, desc, addr, tmplen, cmd);
+
+	addr += tmplen;
+	len -= tmplen;
+	desc += host->desc_sz;
+	_sdhci_adma_write_desc(host, desc, addr, len, cmd);
+
+	return host->desc_sz * 2;
+}
+
 static const struct sdhci_ops sdhci_dwcmshc_ops = {
 	.set_clock		= sdhci_set_clock,
 	.set_bus_width		= sdhci_set_bus_width,
 	.set_uhs_signaling	= sdhci_set_uhs_signaling,
 	.get_max_clock		= sdhci_pltfm_clk_get_max_clock,
 	.reset			= sdhci_reset,
+	.adma_write_desc	= dwcmshc_adma_write_desc,
 };
 
 static const struct sdhci_pltfm_data sdhci_dwcmshc_pdata = {
@@ -36,12 +65,24 @@ static int dwcmshc_probe(struct platform_device *pdev)
 	struct sdhci_host *host;
 	struct dwcmshc_priv *priv;
 	int err;
+	u32 extra;
 
 	host = sdhci_pltfm_init(pdev, &sdhci_dwcmshc_pdata,
 				sizeof(struct dwcmshc_priv));
 	if (IS_ERR(host))
 		return PTR_ERR(host);
 
+	/*
+	 * The DMA descriptor table number is calculated as the maximum
+	 * number of segments times 2, to allow for an alignment
+	 * descriptor for each segment, plus 1 for a nop end descriptor,
+	 * plus extra number for cross 128M boundary handling.
+	 */
+	extra = totalram_pages / (SZ_128M / PAGE_SIZE) + 1;
+	if (extra > SDHCI_MAX_SEGS)
+		extra = SDHCI_MAX_SEGS;
+	host->adma_table_num = SDHCI_MAX_SEGS * 2 + 1 + extra;
+
 	pltfm_host = sdhci_priv(host);
 	priv = sdhci_pltfm_priv(pltfm_host);
 
-- 
2.18.0