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

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Message-ID: <20180725174749.6fc97d4d@xhacker.debian>
Date:   Wed, 25 Jul 2018 17:47:49 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH mmc-next 3/3] mmc: sdhci-of-dwcmshc: solve 128MB DMA
 boundary limitation

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 <Jisheng.Zhang@...aptics.com>
---
 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