Message-ID: <20260123095342.272505-4-yangzh0906@thundersoft.com>
Date: Fri, 23 Jan 2026 17:53:39 +0800
From: Albert Yang <yangzh0906@...ndersoft.com>
To: Ulf Hansson <ulf.hansson@...aro.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Ge Gordon <gordon.ge@....ai>,
	Arnd Bergmann <arnd@...db.de>
Cc: BST Linux Kernel Upstream Group <bst-upstream@...ai.top>,
	linux-mmc@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Albert Yang <yangzh0906@...ndersoft.com>
Subject: [PATCH v5 3/6] mmc: sdhci: add Black Sesame Technologies BST C1200 controller driver

Add SDHCI controller driver for Black Sesame Technologies C1200 SoC.

This driver supports the DWCMSHC SDHCI controller with BST-specific
enhancements including:
- Custom clock management and tuning
- Power management support
- BST-specific register configurations
- Support for eMMC and SD card interfaces
- Hardware limitation workaround for 32-bit DMA addressing

The driver addresses specific hardware constraints where:
- System memory uses 64-bit bus, eMMC controller uses 32-bit bus
- eMMC controller cannot access memory through SMMU due to hardware bug
- All system DRAM is configured outside 4GB boundary (ZONE_DMA32)
- Uses SRAM-based bounce buffer within 32-bit address space

Signed-off-by: Ge Gordon <gordon.ge@....ai>
Signed-off-by: Albert Yang <yangzh0906@...ndersoft.com>
Acked-by: Arnd Bergmann <arnd@...db.de>

---
Changes for v5:
- Split from platform series per Arnd's feedback
- Fix compatible string to match dt-bindings (bst,c1200-sdhci)
- Simplify clock divider calculation with clearer frequency range logic
- Add linux/bits.h and linux/bitfield.h headers
- Remove unused linux/ioport.h header
- Rename SDHCI_TUNING_COUNT to BST_TUNING_COUNT
- Rename BST_EMMC_CTRL_BIT2 to BST_EMMC_CTRL_RST_N
- Fix BST_DEFAULT_MAX_FREQ from 2MHz to 200MHz
- Convert kernel-doc to regular comments (per Adrian Hunter)
- Add sdhci_bst_free_bounce_buffer() helper (per Adrian Hunter)

Changes for v4:
- Rename functions from bst_* to sdhci_bst_*
- Rename driver file to sdhci-of-bst.c
- Replace manual polling with read_poll_timeout()
- Add SDHCI_QUIRK_BROKEN_ADMA quirk
- Add Acked-by: Arnd Bergmann

Changes for v3:
- Simplify dwcmshc_priv structure
- Use devm_platform_ioremap_resource()

Changes for v2:
- Remove COMMON_CLK dependency
- Add ARCH_BST || COMPILE_TEST dependency
- Replace temporary ioremap with persistent mapping
---
 drivers/mmc/host/Kconfig        |  14 +
 drivers/mmc/host/Makefile       |   1 +
 drivers/mmc/host/sdhci-of-bst.c | 521 ++++++++++++++++++++++++++++++++
 3 files changed, 536 insertions(+)
 create mode 100644 drivers/mmc/host/sdhci-of-bst.c

diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index 6d79cc9a79e2..b37e6e014416 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -429,6 +429,20 @@ config MMC_SDHCI_BCM_KONA
 
 	  If you have a controller with this interface, say Y or M here.
 
+config MMC_SDHCI_BST
+	tristate "SDHCI support for Black Sesame Technologies BST C1200 controller"
+	depends on ARCH_BST || COMPILE_TEST
+	depends on MMC_SDHCI_PLTFM
+	depends on OF
+	help
+	  This selects the Secure Digital Host Controller Interface (SDHCI)
+	  for Black Sesame Technologies BST C1200 SoC. The controller is
+	  based on Synopsys DesignWare Cores Mobile Storage Controller but
+	  requires platform-specific workarounds for hardware limitations.
+
+	  If you have a controller with this interface, say Y or M here.
+	  If unsure, say N.
+
 config MMC_SDHCI_F_SDH30
 	tristate "SDHCI support for Fujitsu Semiconductor F_SDH30"
 	depends on MMC_SDHCI_PLTFM
diff --git a/drivers/mmc/host/Makefile b/drivers/mmc/host/Makefile
index 5057fea8afb6..ee412e6b84d6 100644
--- a/drivers/mmc/host/Makefile
+++ b/drivers/mmc/host/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_MMC_MXS)		+= mxs-mmc.o
 obj-$(CONFIG_MMC_SDHCI)		+= sdhci.o
 obj-$(CONFIG_MMC_SDHCI_UHS2)	+= sdhci-uhs2.o
 obj-$(CONFIG_MMC_SDHCI_PCI)	+= sdhci-pci.o
+obj-$(CONFIG_MMC_SDHCI_BST)	        += sdhci-of-bst.o
 sdhci-pci-y			+= sdhci-pci-core.o sdhci-pci-o2micro.o sdhci-pci-arasan.o \
 				   sdhci-pci-dwc-mshc.o sdhci-pci-gli.o
 obj-$(CONFIG_MMC_SDHCI_ACPI)	+= sdhci-acpi.o
diff --git a/drivers/mmc/host/sdhci-of-bst.c b/drivers/mmc/host/sdhci-of-bst.c
new file mode 100644
index 000000000000..c124990a64f4
--- /dev/null
+++ b/drivers/mmc/host/sdhci-of-bst.c
@@ -0,0 +1,521 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * SDHCI driver for Black Sesame Technologies C1200 controller
+ *
+ * Copyright (c) 2025 Black Sesame Technologies
+ */
+
+#include <linux/bits.h>
+#include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/dma-mapping.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/platform_device.h>
+#include "sdhci.h"
+#include "sdhci-pltfm.h"
+
+/* SDHCI register extensions */
+#define SDHCI_CLOCK_PLL_EN		0x0008
+#define SDHCI_VENDOR_PTR_R		0xE8
+
+/* BST-specific tuning parameters */
+#define BST_TUNING_COUNT		0x20
+
+/* Synopsys vendor specific registers */
+#define SDHC_EMMC_CTRL_R_OFFSET		0x2C
+#define MBIU_CTRL			0x510
+
+/* MBIU burst control bits */
+#define BURST_INCR16_EN			BIT(3)
+#define BURST_INCR8_EN			BIT(2)
+#define BURST_INCR4_EN			BIT(1)
+#define BURST_EN			(BURST_INCR16_EN | BURST_INCR8_EN | BURST_INCR4_EN)
+#define MBIU_BURST_MASK			GENMASK(3, 0)
+
+/* CRM (Clock/Reset/Management) register offsets */
+#define SDEMMC_CRM_BCLK_DIV_CTRL	0x08
+#define SDEMMC_CRM_TIMER_DIV_CTRL	0x0C
+#define SDEMMC_CRM_RX_CLK_CTRL		0x14
+#define SDEMMC_CRM_VOL_CTRL		0x1C
+#define REG_WR_PROTECT			0x88
+#define DELAY_CHAIN_SEL			0x94
+
+/* CRM register values and bit definitions */
+#define REG_WR_PROTECT_KEY		0x1234abcd
+#define BST_VOL_STABLE_ON		BIT(7)
+#define BST_TIMER_DIV_MASK		GENMASK(7, 0)
+#define BST_TIMER_DIV_VAL		0x20
+#define BST_TIMER_LOAD_BIT		BIT(8)
+#define BST_BCLK_EN_BIT			BIT(10)
+#define BST_RX_UPDATE_BIT		BIT(11)
+#define BST_EMMC_CTRL_RST_N		BIT(2)	/* eMMC card reset control */
+
+/* Clock frequency limits */
+#define BST_DEFAULT_MAX_FREQ		200000000UL	/* 200 MHz */
+#define BST_DEFAULT_MIN_FREQ		400000UL	/* 400 kHz */
+
+/* Clock control bit definitions */
+#define BST_CLOCK_DIV_MASK		GENMASK(7, 0)
+#define BST_CLOCK_DIV_SHIFT		8
+#define BST_BCLK_DIV_MASK		GENMASK(9, 0)
+
+/* Clock frequency thresholds */
+#define BST_CLOCK_THRESHOLD_LOW		1500
+
+/* Clock stability polling parameters */
+#define BST_CLK_STABLE_POLL_US		1000	/* Poll interval in microseconds */
+#define BST_CLK_STABLE_TIMEOUT_US	20000	/* Timeout for internal clock stabilization (us) */
+
+struct sdhci_bst_priv {
+	void __iomem *crm_reg_base;
+};
+
+union sdhci_bst_rx_ctrl {
+	struct {
+		u32 rx_revert:1,
+		    rx_clk_sel_sec:1,
+		    rx_clk_div:4,
+		    rx_clk_phase_inner:2,
+		    rx_clk_sel_first:1,
+		    rx_clk_phase_out:2,
+		    rx_clk_en:1,
+		    res0:20;
+	};
+	u32 reg;
+};
+
+static u32 sdhci_bst_crm_read(struct sdhci_pltfm_host *pltfm_host, u32 offset)
+{
+	struct sdhci_bst_priv *priv = sdhci_pltfm_priv(pltfm_host);
+
+	return readl(priv->crm_reg_base + offset);
+}
+
+static void sdhci_bst_crm_write(struct sdhci_pltfm_host *pltfm_host, u32 offset, u32 value)
+{
+	struct sdhci_bst_priv *priv = sdhci_pltfm_priv(pltfm_host);
+
+	writel(value, priv->crm_reg_base + offset);
+}
+
+static int sdhci_bst_wait_int_clk(struct sdhci_host *host)
+{
+	u16 clk;
+
+	if (read_poll_timeout(sdhci_readw, clk, (clk & SDHCI_CLOCK_INT_STABLE),
+			      BST_CLK_STABLE_POLL_US, BST_CLK_STABLE_TIMEOUT_US, false,
+			      host, SDHCI_CLOCK_CONTROL))
+		return -EBUSY;
+	return 0;
+}
+
+static unsigned int sdhci_bst_get_max_clock(struct sdhci_host *host)
+{
+	return BST_DEFAULT_MAX_FREQ;
+}
+
+static unsigned int sdhci_bst_get_min_clock(struct sdhci_host *host)
+{
+	return BST_DEFAULT_MIN_FREQ;
+}
+
+static void sdhci_bst_enable_clk(struct sdhci_host *host, unsigned int clk)
+{
+	struct sdhci_pltfm_host *pltfm_host;
+	unsigned int div;
+	u32 val;
+	union sdhci_bst_rx_ctrl rx_reg;
+
+	pltfm_host = sdhci_priv(host);
+
+	/* Calculate clock divider based on target frequency */
+	if (clk == 0) {
+		div = 0;
+	} else if (clk < BST_DEFAULT_MIN_FREQ) {
+		/* Below minimum: use max divider to get closest to min freq */
+		div = BST_DEFAULT_MAX_FREQ / BST_DEFAULT_MIN_FREQ;
+	} else if (clk <= BST_DEFAULT_MAX_FREQ) {
+		/* Normal range: calculate divider directly */
+		div = BST_DEFAULT_MAX_FREQ / clk;
+	} else {
+		/* Above maximum: no division needed */
+		div = 1;
+	}
+
+	clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+	clk &= ~SDHCI_CLOCK_CARD_EN;
+	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+	clk &= ~SDHCI_CLOCK_PLL_EN;
+	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_TIMER_DIV_CTRL);
+	val &= ~BST_TIMER_LOAD_BIT;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_TIMER_DIV_CTRL, val);
+
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_TIMER_DIV_CTRL);
+	val &= ~BST_TIMER_DIV_MASK;
+	val |= BST_TIMER_DIV_VAL;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_TIMER_DIV_CTRL, val);
+
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_TIMER_DIV_CTRL);
+	val |= BST_TIMER_LOAD_BIT;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_TIMER_DIV_CTRL, val);
+
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL);
+	val &= ~BST_RX_UPDATE_BIT;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL, val);
+
+	rx_reg.reg = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL);
+
+	rx_reg.rx_revert = 0;
+	rx_reg.rx_clk_sel_sec = 1;
+	rx_reg.rx_clk_div = 4;
+	rx_reg.rx_clk_phase_inner = 2;
+	rx_reg.rx_clk_sel_first = 0;
+	rx_reg.rx_clk_phase_out = 2;
+
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL, rx_reg.reg);
+
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL);
+	val |= BST_RX_UPDATE_BIT;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL, val);
+
+	/* Disable clock first */
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL);
+	val &= ~BST_BCLK_EN_BIT;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL, val);
+
+	/* Setup clock divider */
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL);
+	val &= ~BST_BCLK_DIV_MASK;
+	val |= div;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL, val);
+
+	/* Enable clock */
+	val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL);
+	val |= BST_BCLK_EN_BIT;
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL, val);
+
+	/* RMW the clock divider bits to avoid clobbering other fields */
+	clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+	clk &= ~(BST_CLOCK_DIV_MASK << BST_CLOCK_DIV_SHIFT);
+	clk |= (div & BST_CLOCK_DIV_MASK) << BST_CLOCK_DIV_SHIFT;
+	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+	clk = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+	clk |= SDHCI_CLOCK_PLL_EN;
+	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+	clk |= SDHCI_CLOCK_CARD_EN;
+	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+
+	clk |= SDHCI_CLOCK_INT_EN;
+	sdhci_writew(host, clk, SDHCI_CLOCK_CONTROL);
+}
+
+static void sdhci_bst_set_clock(struct sdhci_host *host, unsigned int clock)
+{
+	/* Turn off card/internal/PLL clocks when clock==0 to avoid idle power */
+	u32 clk_reg = sdhci_readw(host, SDHCI_CLOCK_CONTROL);
+
+	if (!clock) {
+		clk_reg &= ~(SDHCI_CLOCK_CARD_EN | SDHCI_CLOCK_INT_EN | SDHCI_CLOCK_PLL_EN);
+		sdhci_writew(host, clk_reg, SDHCI_CLOCK_CONTROL);
+		return;
+	}
+	sdhci_bst_enable_clk(host, clock);
+}
+
+/*
+ * sdhci_bst_reset - Reset the SDHCI host controller with special
+ * handling for eMMC card reset control.
+ */
+static void sdhci_bst_reset(struct sdhci_host *host, u8 mask)
+{
+	u16 vendor_ptr, emmc_ctrl_reg;
+	u32 reg;
+
+	if (host->mmc->caps2 & MMC_CAP2_NO_SD) {
+		vendor_ptr = sdhci_readw(host, SDHCI_VENDOR_PTR_R);
+		emmc_ctrl_reg = vendor_ptr + SDHC_EMMC_CTRL_R_OFFSET;
+
+		reg = sdhci_readw(host, emmc_ctrl_reg);
+		reg &= ~BST_EMMC_CTRL_RST_N;
+		sdhci_writew(host, reg, emmc_ctrl_reg);
+		sdhci_reset(host, mask);
+		usleep_range(10, 20);
+		reg = sdhci_readw(host, emmc_ctrl_reg);
+		reg |= BST_EMMC_CTRL_RST_N;
+		sdhci_writew(host, reg, emmc_ctrl_reg);
+	} else {
+		sdhci_reset(host, mask);
+	}
+}
+
+/* Set timeout control register to maximum value (0xE) */
+static void sdhci_bst_set_timeout(struct sdhci_host *host, struct mmc_command *cmd)
+{
+	sdhci_writeb(host, 0xE, SDHCI_TIMEOUT_CONTROL);
+}
+
+/*
+ * sdhci_bst_set_power - Set power mode and voltage, also configures
+ * MBIU burst mode control based on power state.
+ */
+static void sdhci_bst_set_power(struct sdhci_host *host, unsigned char mode,
+				unsigned short vdd)
+{
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+	u32 reg;
+	u32 val;
+
+	sdhci_set_power(host, mode, vdd);
+
+	if (mode == MMC_POWER_OFF) {
+		/* Disable MBIU burst mode */
+		reg = sdhci_readw(host, MBIU_CTRL);
+		reg &= ~BURST_EN; /* Clear all burst enable bits */
+		sdhci_writew(host, reg, MBIU_CTRL);
+
+		/* Disable CRM BCLK */
+		val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL);
+		val &= ~BST_BCLK_EN_BIT;
+		sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_BCLK_DIV_CTRL, val);
+
+		/* Disable RX clock */
+		val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL);
+		val &= ~BST_RX_UPDATE_BIT;
+		sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_RX_CLK_CTRL, val);
+
+		/* Turn off voltage stable power */
+		val = sdhci_bst_crm_read(pltfm_host, SDEMMC_CRM_VOL_CTRL);
+		val &= ~BST_VOL_STABLE_ON;
+		sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_VOL_CTRL, val);
+	} else {
+		/* Configure burst mode only when powered on */
+		reg = sdhci_readw(host, MBIU_CTRL);
+		reg &= ~MBIU_BURST_MASK; /* Clear burst related bits */
+		reg |= BURST_EN; /* Enable burst mode for better bandwidth */
+		sdhci_writew(host, reg, MBIU_CTRL);
+	}
+}
+
+/*
+ * sdhci_bst_execute_tuning - Execute tuning procedure by trying different
+ * delay chain values and selecting the optimal one.
+ */
+static int sdhci_bst_execute_tuning(struct sdhci_host *host, u32 opcode)
+{
+	struct sdhci_pltfm_host *pltfm_host;
+	int ret = 0, error;
+	int first_start = -1, first_end = -1, best = 0;
+	int second_start = -1, second_end = -1, has_failure = 0;
+	int i;
+
+	pltfm_host = sdhci_priv(host);
+
+	for (i = 0; i < BST_TUNING_COUNT; i++) {
+		/* Protected write */
+		sdhci_bst_crm_write(pltfm_host, REG_WR_PROTECT, REG_WR_PROTECT_KEY);
+		/* Write tuning value */
+		sdhci_bst_crm_write(pltfm_host, DELAY_CHAIN_SEL, (1ul << i) - 1);
+
+		/* Wait for internal clock stable before tuning */
+		if (sdhci_bst_wait_int_clk(host)) {
+			dev_err(mmc_dev(host->mmc), "Internal clock never stabilised\n");
+			return -EBUSY;
+		}
+
+		ret = mmc_send_tuning(host->mmc, opcode, &error);
+		if (ret != 0) {
+			has_failure = 1;
+		} else {
+			if (has_failure == 0) {
+				if (first_start == -1)
+					first_start = i;
+				first_end = i;
+			} else {
+				if (second_start == -1)
+					second_start = i;
+				second_end = i;
+			}
+		}
+	}
+
+	/* Calculate best tuning value */
+	if (first_end - first_start >= second_end - second_start)
+		best = ((first_end - first_start) >> 1) + first_start;
+	else
+		best = ((second_end - second_start) >> 1) + second_start;
+
+	if (best < 0)
+		best = 0;
+
+	sdhci_bst_crm_write(pltfm_host, DELAY_CHAIN_SEL, (1ul << best) - 1);
+	/* Confirm internal clock stable after setting best tuning value */
+	if (sdhci_bst_wait_int_clk(host)) {
+		dev_err(mmc_dev(host->mmc), "Internal clock never stabilised\n");
+		return -EBUSY;
+	}
+
+	return 0;
+}
+
+/* Enable voltage stable power for voltage switch */
+static void sdhci_bst_voltage_switch(struct sdhci_host *host)
+{
+	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
+
+	/* Enable voltage stable power */
+	sdhci_bst_crm_write(pltfm_host, SDEMMC_CRM_VOL_CTRL, BST_VOL_STABLE_ON);
+}
+
+static const struct sdhci_ops sdhci_bst_ops = {
+	.set_clock		= sdhci_bst_set_clock,
+	.set_bus_width		= sdhci_set_bus_width,
+	.set_uhs_signaling	= sdhci_set_uhs_signaling,
+	.get_min_clock		= sdhci_bst_get_min_clock,
+	.get_max_clock		= sdhci_bst_get_max_clock,
+	.reset			= sdhci_bst_reset,
+	.set_power		= sdhci_bst_set_power,
+	.set_timeout		= sdhci_bst_set_timeout,
+	.platform_execute_tuning = sdhci_bst_execute_tuning,
+	.voltage_switch		= sdhci_bst_voltage_switch,
+};
+
+static const struct sdhci_pltfm_data sdhci_bst_pdata = {
+	.ops = &sdhci_bst_ops,
+	.quirks = SDHCI_QUIRK_BROKEN_ADMA |
+		  SDHCI_QUIRK_DELAY_AFTER_POWER |
+		  SDHCI_QUIRK_CAP_CLOCK_BASE_BROKEN |
+		  SDHCI_QUIRK_INVERTED_WRITE_PROTECT,
+	.quirks2 = SDHCI_QUIRK2_BROKEN_DDR50 |
+		   SDHCI_QUIRK2_TUNING_WORK_AROUND |
+		   SDHCI_QUIRK2_ACMD23_BROKEN,
+};
+
+static void sdhci_bst_free_bounce_buffer(struct sdhci_host *host)
+{
+	if (host->bounce_buffer) {
+		dma_free_coherent(mmc_dev(host->mmc), host->bounce_buffer_size,
+				  host->bounce_buffer, host->bounce_addr);
+		host->bounce_buffer = NULL;
+	}
+	of_reserved_mem_device_release(mmc_dev(host->mmc));
+}
+
+static int sdhci_bst_alloc_bounce_buffer(struct sdhci_host *host)
+{
+	struct mmc_host *mmc = host->mmc;
+	unsigned int bounce_size;
+	int ret;
+
+	/* Fixed SRAM bounce size to 32KB: verified config under 32-bit DMA addressing limit */
+	bounce_size = SZ_32K;
+
+	ret = of_reserved_mem_device_init_by_idx(mmc_dev(mmc), mmc_dev(mmc)->of_node, 0);
+	if (ret) {
+		dev_err(mmc_dev(mmc), "Failed to initialize reserved memory\n");
+		return ret;
+	}
+
+	host->bounce_buffer = dma_alloc_coherent(mmc_dev(mmc), bounce_size,
+						 &host->bounce_addr, GFP_KERNEL);
+	if (!host->bounce_buffer)
+		return -ENOMEM;
+
+	host->bounce_buffer_size = bounce_size;
+
+	return 0;
+}
+
+static int sdhci_bst_probe(struct platform_device *pdev)
+{
+	struct sdhci_pltfm_host *pltfm_host;
+	struct sdhci_host *host;
+	struct sdhci_bst_priv *priv;
+	int err;
+
+	host = sdhci_pltfm_init(pdev, &sdhci_bst_pdata, sizeof(struct sdhci_bst_priv));
+	if (IS_ERR(host))
+		return PTR_ERR(host);
+
+	pltfm_host = sdhci_priv(host);
+	priv = sdhci_pltfm_priv(pltfm_host); /* Get platform private data */
+
+	err = mmc_of_parse(host->mmc);
+	if (err)
+		return err;
+
+	sdhci_get_of_property(pdev);
+
+	/* Get CRM registers from the second reg entry */
+	priv->crm_reg_base = devm_platform_ioremap_resource(pdev, 1);
+	if (IS_ERR(priv->crm_reg_base)) {
+		err = PTR_ERR(priv->crm_reg_base);
+		return err;
+	}
+
+	/*
+	 * Silicon constraints for BST C1200:
+	 * - System RAM base is 0x800000000 (above 32-bit addressable range)
+	 * - The eMMC controller DMA engine is limited to 32-bit addressing
+	 * - SMMU cannot be used on this path due to hardware design flaws
+	 * - These are fixed in silicon and cannot be changed in software
+	 *
+	 * Bus/controller mapping:
+	 * - No registers are available to reprogram the address mapping
+	 * - The 32-bit DMA limit is a hard constraint of the controller IP
+	 *
+	 * Given these constraints, an SRAM-based bounce buffer in the 32-bit
+	 * address space is required to enable eMMC DMA on this platform.
+	 */
+	err = sdhci_bst_alloc_bounce_buffer(host);
+	if (err) {
+		dev_err(&pdev->dev, "Failed to allocate bounce buffer: %d\n", err);
+		return err;
+	}
+
+	err = sdhci_add_host(host);
+	if (err)
+		goto err_free_bounce_buffer;
+
+	return 0;
+
+err_free_bounce_buffer:
+	sdhci_bst_free_bounce_buffer(host);
+
+	return err;
+}
+
+static void sdhci_bst_remove(struct platform_device *pdev)
+{
+	struct sdhci_host *host = platform_get_drvdata(pdev);
+
+	sdhci_bst_free_bounce_buffer(host);
+	sdhci_pltfm_remove(pdev);
+}
+
+static const struct of_device_id sdhci_bst_ids[] = {
+	{ .compatible = "bst,c1200-sdhci" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, sdhci_bst_ids);
+
+static struct platform_driver sdhci_bst_driver = {
+	.driver = {
+		.name = "sdhci-bst",
+		.of_match_table = sdhci_bst_ids,
+	},
+	.probe = sdhci_bst_probe,
+	.remove = sdhci_bst_remove,
+};
+module_platform_driver(sdhci_bst_driver);
+
+MODULE_DESCRIPTION("Black Sesame Technologies SDHCI driver (BST)");
+MODULE_AUTHOR("Black Sesame Technologies Co., Ltd.");
+MODULE_LICENSE("GPL");
-- 
2.43.0

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