mmc: Driver for CB710/720 memory card reader (MMC part)

The code is divided in two parts. There is a virtual 'bus' driver
that handles PCI device and registers three new devices one per card
reader type. The other driver handles SD/MMC part of the reader.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>

7 files changed, 653 insertions, 0 deletions

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 6d1ac18..68ab39d 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -235,5 +235,6 @@ config ISL29003
 
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
+source "drivers/misc/cb710/Kconfig"
 
 endif # MISC_DEVICES
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 7871f05..36f733c 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -21,3 +21,4 @@ obj-$(CONFIG_HP_ILO)		+= hpilo.o
 obj-$(CONFIG_ISL29003)		+= isl29003.o
 obj-$(CONFIG_C2PORT)		+= c2port/
 obj-y				+= eeprom/
+obj-y				+= cb710/
diff --git a/drivers/misc/cb710/Kconfig b/drivers/misc/cb710/Kconfig
new file mode 100644
index 0000000..0b55079
--- /dev/null
+++ b/drivers/misc/cb710/Kconfig
@@ -0,0 +1,21 @@
+config CB710_CORE
+	tristate "ENE CB710/720 Flash memory card reader support"
+	depends on PCI
+	help
+	  This option enables support for PCI ENE CB710/720 Flash memory card
+	  reader found in some laptops (ie. some versions of HP Compaq nx9500).
+
+	  You will also have to select some flash card format drivers (MMC/SD,
+	  MemoryStick).
+
+	  This driver can also be built as a module. If so, the module
+	  will be called cb710.
+
+config CB710_DEBUG
+	bool "Enable driver debugging"
+	depends on CB710_CORE != n
+	default n
+	help
+	  This is an option for use by developers; most people should
+	  say N here.  This adds a lot of debugging output to dmesg.
+
diff --git a/drivers/misc/cb710/Makefile b/drivers/misc/cb710/Makefile
new file mode 100644
index 0000000..62d51ac
--- /dev/null
+++ b/drivers/misc/cb710/Makefile
@@ -0,0 +1,4 @@
+obj-$(CONFIG_CB710_CORE)	+= cb710.o
+
+cb710-y				:= core.o sgbuf2.o
+cb710-$(CONFIG_CB710_DEBUG)	+= debug.o
diff --git a/drivers/misc/cb710/core.c b/drivers/misc/cb710/core.c
new file mode 100644
index 0000000..b14eab0
--- /dev/null
+++ b/drivers/misc/cb710/core.c
@@ -0,0 +1,357 @@
+/*
+ *  cb710/core.c
+ *
+ *  Copyright by Michał Mirosław, 2008-2009
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/pci.h>
+#include <linux/spinlock.h>
+#include <linux/idr.h>
+#include <linux/cb710.h>
+
+static DEFINE_IDA(cb710_ida);
+static DEFINE_SPINLOCK(cb710_ida_lock);
+
+void cb710_pci_update_config_reg(struct pci_dev *pdev,
+	int reg, uint32_t mask, uint32_t xor)
+{
+	u32 rval;
+
+	pci_read_config_dword(pdev, reg, &rval);
+	rval = (rval & mask) ^ xor;
+	pci_write_config_dword(pdev, reg, rval);
+}
+EXPORT_SYMBOL_GPL(cb710_pci_update_config_reg);
+
+/* Some magic writes based on Windows driver init code */
+static int __devinit cb710_pci_configure(struct pci_dev *pdev)
+{
+	unsigned int devfn = PCI_DEVFN(PCI_SLOT(pdev->devfn), 0);
+	struct pci_dev *pdev0 = pci_get_slot(pdev->bus, devfn);
+	u32 val;
+
+	cb710_pci_update_config_reg(pdev, 0x48,
+		~0x000000FF, 0x0000003F);
+
+	pci_read_config_dword(pdev, 0x48, &val);
+	if (val & 0x80000000)
+		return 0;
+
+	if (!pdev0)
+		return -ENODEV;
+
+	if (pdev0->vendor == PCI_VENDOR_ID_ENE
+	    && pdev0->device == PCI_DEVICE_ID_ENE_720) {
+		cb710_pci_update_config_reg(pdev0, 0x8C,
+			~0x00F00000, 0x00100000);
+		cb710_pci_update_config_reg(pdev0, 0xB0,
+			~0x08000000, 0x08000000);
+	}
+
+	cb710_pci_update_config_reg(pdev0, 0x8C,
+		~0x00000F00, 0x00000200);
+	cb710_pci_update_config_reg(pdev0, 0x90,
+		~0x00060000, 0x00040000);
+
+	pci_dev_put(pdev0);
+
+	return 0;
+}
+
+static irqreturn_t cb710_irq_handler(int irq, void *data)
+{
+	struct cb710_chip *chip = data;
+	struct cb710_slot *slot = &chip->slot[0];
+	irqreturn_t handled = IRQ_NONE;
+	unsigned nr;
+
+	spin_lock(&chip->irq_lock); /* incl. smp_rmb() */
+
+	for (nr = chip->slots; nr; ++slot, --nr) {
+		cb710_irq_handler_t handler_func = slot->irq_handler;
+		if (handler_func && handler_func(slot))
+			handled = IRQ_HANDLED;
+	}
+
+	spin_unlock(&chip->irq_lock);
+
+	return handled;
+}
+
+static void cb710_release_slot(struct device *dev)
+{
+#ifdef CONFIG_CB710_DEBUG_ASSUMPTIONS
+	struct cb710_slot *slot = cb710_pdev_to_slot(to_platform_device(dev));
+	struct cb710_chip *chip = cb710_slot_to_chip(slot);
+
+	/* slot struct can be freed now */
+	atomic_dec(&chip->slot_refs_count);
+#endif
+}
+
+static int __devinit cb710_register_slot(struct cb710_chip *chip,
+	unsigned slot_mask, unsigned io_offset, const char *name)
+{
+	int nr = chip->slots;
+	struct cb710_slot *slot = &chip->slot[nr];
+	int err;
+
+	dev_dbg(cb710_chip_dev(chip),
+		"register: %s.%d; slot %d; mask %d; IO offset: 0x%02X\n",
+		name, chip->platform_id, nr, slot_mask, io_offset);
+
+	/* slot->irq_handler == NULL here; this needs to be
+	 * seen before platform_device_register() */
+	++chip->slots;
+	smp_wmb();
+
+	slot->iobase = chip->iobase + io_offset;
+	slot->pdev.name = name;
+	slot->pdev.id = chip->platform_id;
+	slot->pdev.dev.parent = &chip->pdev->dev;
+	slot->pdev.dev.release = cb710_release_slot;
+
+	err = platform_device_register(&slot->pdev);
+
+#ifdef CONFIG_CB710_DEBUG_ASSUMPTIONS
+	atomic_inc(&chip->slot_refs_count);
+#endif
+
+	if (err) {
+		/* device_initialize() called from platform_device_register()
+		 * wants this on error path */
+		platform_device_put(&slot->pdev);
+
+		/* slot->irq_handler == NULL here anyway, so no lock needed */
+		--chip->slots;
+		return err;
+	}
+
+	chip->slot_mask |= slot_mask;
+
+	return 0;
+}
+
+static void cb710_unregister_slot(struct cb710_chip *chip,
+	unsigned slot_mask)
+{
+	int nr = chip->slots - 1;
+
+	if (!(chip->slot_mask & slot_mask))
+		return;
+
+	platform_device_unregister(&chip->slot[nr].pdev);
+
+	/* complementary to spin_unlock() in cb710_set_irq_handler() */
+	smp_rmb();
+	BUG_ON(chip->slot[nr].irq_handler != NULL);
+
+	/* slot->irq_handler == NULL here, so no lock needed */
+	--chip->slots;
+	chip->slot_mask &= ~slot_mask;
+}
+
+void cb710_set_irq_handler(struct cb710_slot *slot,
+	cb710_irq_handler_t handler)
+{
+	struct cb710_chip *chip = cb710_slot_to_chip(slot);
+	unsigned long flags;
+
+	spin_lock_irqsave(&chip->irq_lock, flags);
+	slot->irq_handler = handler;
+	spin_unlock_irqrestore(&chip->irq_lock, flags);
+}
+EXPORT_SYMBOL_GPL(cb710_set_irq_handler);
+
+#ifdef CONFIG_PM
+
+static int cb710_suspend(struct pci_dev *pdev, pm_message_t state)
+{
+	struct cb710_chip *chip = pci_get_drvdata(pdev);
+
+	free_irq(pdev->irq, chip);
+	pci_save_state(pdev);
+	pci_disable_device(pdev);
+	if (state.event & PM_EVENT_SLEEP)
+		pci_set_power_state(pdev, PCI_D3cold);
+	return 0;
+}
+
+static int cb710_resume(struct pci_dev *pdev)
+{
+	struct cb710_chip *chip = pci_get_drvdata(pdev);
+	int err;
+
+	pci_set_power_state(pdev, PCI_D0);
+	pci_restore_state(pdev);
+	err = pcim_enable_device(pdev);
+	if (err)
+		return err;
+
+	return devm_request_irq(&pdev->dev, pdev->irq,
+		cb710_irq_handler, IRQF_SHARED, KBUILD_MODNAME, chip);
+}
+
+#endif /* CONFIG_PM */
+
+static int __devinit cb710_probe(struct pci_dev *pdev,
+	const struct pci_device_id *ent)
+{
+	struct cb710_chip *chip;
+	unsigned long flags;
+	u32 val;
+	int err;
+	int n = 0;
+
+	err = cb710_pci_configure(pdev);
+	if (err)
+		return err;
+
+	/* this is actually magic... */
+	pci_read_config_dword(pdev, 0x48, &val);
+	if (!(val & 0x80000000)) {
+		pci_write_config_dword(pdev, 0x48, val|0x71000000);
+		pci_read_config_dword(pdev, 0x48, &val);
+	}
+
+	dev_dbg(&pdev->dev, "PCI config[0x48] = 0x%08X\n", val);
+	if (!(val & 0x70000000))
+		return -ENODEV;
+	val = (val >> 28) & 7;
+	if (val & CB710_SLOT_MMC)
+		++n;
+	if (val & CB710_SLOT_MS)
+		++n;
+	if (val & CB710_SLOT_SM)
+		++n;
+
+	chip = devm_kzalloc(&pdev->dev,
+		sizeof(*chip) + n * sizeof(*chip->slot), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
+
+	err = pcim_enable_device(pdev);
+	if (err)
+		return err;
+
+	err = pcim_iomap_regions(pdev, 0x0001, KBUILD_MODNAME);
+	if (err)
+		return err;
+
+	chip->pdev = pdev;
+	chip->iobase = pcim_iomap_table(pdev)[0];
+
+	pci_set_drvdata(pdev, chip);
+
+	err = devm_request_irq(&pdev->dev, pdev->irq,
+		cb710_irq_handler, IRQF_SHARED, KBUILD_MODNAME, chip);
+	if (err)
+		return err;
+
+	do {
+		if (!ida_pre_get(&cb710_ida, GFP_KERNEL))
+			return -ENOMEM;
+
+		spin_lock_irqsave(&cb710_ida_lock, flags);
+		err = ida_get_new(&cb710_ida, &chip->platform_id);
+		spin_unlock_irqrestore(&cb710_ida_lock, flags);
+
+		if (err && err != -EAGAIN)
+			return err;
+	} while (err);
+
+
+	dev_info(&pdev->dev, "id %d, IO 0x%p, IRQ %d\n",
+		chip->platform_id, chip->iobase, pdev->irq);
+
+	if (val & CB710_SLOT_MMC) {	/* MMC/SD slot */
+		err = cb710_register_slot(chip,
+			CB710_SLOT_MMC, 0x00, "cb710-mmc");
+		if (err)
+			return err;
+	}
+
+	if (val & CB710_SLOT_MS) {	/* MemoryStick slot */
+		err = cb710_register_slot(chip,
+			CB710_SLOT_MS, 0x40, "cb710-ms");
+		if (err)
+			goto unreg_mmc;
+	}
+
+	if (val & CB710_SLOT_SM) {	/* SmartMedia slot */
+		err = cb710_register_slot(chip,
+			CB710_SLOT_SM, 0x60, "cb710-sm");
+		if (err)
+			goto unreg_ms;
+	}
+
+	return 0;
+unreg_ms:
+	cb710_unregister_slot(chip, CB710_SLOT_MS);
+unreg_mmc:
+	cb710_unregister_slot(chip, CB710_SLOT_MMC);
+
+#ifdef CONFIG_CB710_DEBUG_ASSUMPTIONS
+	BUG_ON(atomic_read(&chip->slot_refs_count) != 0);
+#endif
+	return err;
+}
+
+static void __devexit cb710_remove_one(struct pci_dev *pdev)
+{
+	struct cb710_chip *chip = pci_get_drvdata(pdev);
+	unsigned long flags;
+
+	cb710_unregister_slot(chip, CB710_SLOT_SM);
+	cb710_unregister_slot(chip, CB710_SLOT_MS);
+	cb710_unregister_slot(chip, CB710_SLOT_MMC);
+#ifdef CONFIG_CB710_DEBUG_ASSUMPTIONS
+	BUG_ON(atomic_read(&chip->slot_refs_count) != 0);
+#endif
+
+	spin_lock_irqsave(&cb710_ida_lock, flags);
+	ida_remove(&cb710_ida, chip->platform_id);
+	spin_unlock_irqrestore(&cb710_ida_lock, flags);
+}
+
+static const struct pci_device_id cb710_pci_tbl[] = {
+	{ PCI_VENDOR_ID_ENE, PCI_DEVICE_ID_ENE_CB710_FLASH,
+		PCI_ANY_ID, PCI_ANY_ID, },
+	{ 0, }
+};
+
+static struct pci_driver cb710_driver = {
+	.name = KBUILD_MODNAME,
+	.id_table = cb710_pci_tbl,
+	.probe = cb710_probe,
+	.remove = __devexit_p(cb710_remove_one),
+#ifdef CONFIG_PM
+	.suspend = cb710_suspend,
+	.resume = cb710_resume,
+#endif
+};
+
+static int __init cb710_init_module(void)
+{
+	return pci_register_driver(&cb710_driver);
+}
+
+static void __exit cb710_cleanup_module(void)
+{
+	pci_unregister_driver(&cb710_driver);
+	ida_destroy(&cb710_ida);
+}
+
+module_init(cb710_init_module);
+module_exit(cb710_cleanup_module);
+
+MODULE_AUTHOR("Michał Mirosław <mirq-linux@rere.qmqm.pl>");
+MODULE_DESCRIPTION("ENE CB710 memory card reader driver");
+MODULE_LICENSE("GPL");
+MODULE_DEVICE_TABLE(pci, cb710_pci_tbl);
diff --git a/drivers/misc/cb710/debug.c b/drivers/misc/cb710/debug.c
new file mode 100644
index 0000000..9da11bc
--- /dev/null
+++ b/drivers/misc/cb710/debug.c
@@ -0,0 +1,119 @@
+/*
+ *  cb710/debug.c
+ *
+ *  Copyright by Michał Mirosław, 2008-2009
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/cb710.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+
+#define CB710_REG_COUNT		0x80
+
+static const u16 allow[CB710_REG_COUNT/16] = {
+	0xFFF0, 0xFFFF, 0xFFFF, 0xFFFF,
+	0xFFF0, 0xFFFF, 0xFFFF, 0xFFFF,
+};
+static const char *const prefix[ARRAY_SIZE(allow)] = {
+	"MMC", "MMC", "MMC", "MMC",
+	"MS?", "MS?", "SM?", "SM?"
+};
+
+static inline int allow_reg_read(unsigned block, unsigned offset, unsigned bits)
+{
+	unsigned mask = (1 << bits/8) - 1;
+	offset *= bits/8;
+	return ((allow[block] >> offset) & mask) == mask;
+}
+
+#define CB710_READ_REGS_TEMPLATE(t)					\
+static void cb710_read_regs_##t(void __iomem *iobase,			\
+	u##t *reg, unsigned select)					\
+{									\
+	unsigned i, j;							\
+									\
+	for (i = 0; i < ARRAY_SIZE(allow); ++i, reg += 16/(t/8)) {	\
+		if (!select & (1 << i))					\
+			continue;					\
+									\
+		for (j = 0; j < 0x10/(t/8); ++j) {			\
+			if (!allow_reg_read(i, j, t))			\
+				continue;				\
+			reg[j] = ioread##t(iobase			\
+				+ (i << 4) + (j * (t/8)));		\
+		}							\
+	}								\
+}
+
+static const char cb710_regf_8[] = "%02X";
+static const char cb710_regf_16[] = "%04X";
+static const char cb710_regf_32[] = "%08X";
+static const char cb710_xes[] = "xxxxxxxx";
+
+#define CB710_DUMP_REGS_TEMPLATE(t)					\
+static void cb710_dump_regs_##t(struct device *dev,			\
+	const u##t *reg, unsigned select)				\
+{									\
+	const char *const xp = &cb710_xes[8 - t/4];			\
+	const char *const format = cb710_regf_##t;			\
+									\
+	char msg[100], *p;						\
+	unsigned i, j;							\
+									\
+	for (i = 0; i < ARRAY_SIZE(allow); ++i, reg += 16/(t/8)) {	\
+		if (!(select & (1 << i)))				\
+			continue;					\
+		p = msg;						\
+		for (j = 0; j < 0x10/(t/8); ++j) {			\
+			*p++ = ' ';					\
+			if (j == 8/(t/8))				\
+				*p++ = ' ';				\
+			if (allow_reg_read(i, j, t))			\
+				p += sprintf(p, format, reg[j]);	\
+			else						\
+				p += sprintf(p, "%s", xp);		\
+		}							\
+		dev_dbg(dev, "%s 0x%02X %s\n", prefix[i], i << 4, msg);	\
+	}								\
+}
+
+#define CB710_READ_AND_DUMP_REGS_TEMPLATE(t)				\
+static void cb710_read_and_dump_regs_##t(struct cb710_chip *chip,	\
+	unsigned select)						\
+{									\
+	u##t regs[CB710_REG_COUNT/sizeof(u##t)];			\
+									\
+	memset(&regs, 0, sizeof(regs));					\
+	cb710_read_regs_##t(chip->iobase, regs, select);		\
+	cb710_dump_regs_##t(cb710_chip_dev(chip), regs, select);	\
+}
+
+#define CB710_REG_ACCESS_TEMPLATES(t)		\
+  CB710_READ_REGS_TEMPLATE(t)			\
+  CB710_DUMP_REGS_TEMPLATE(t)			\
+  CB710_READ_AND_DUMP_REGS_TEMPLATE(t)
+
+CB710_REG_ACCESS_TEMPLATES(8)
+CB710_REG_ACCESS_TEMPLATES(16)
+CB710_REG_ACCESS_TEMPLATES(32)
+
+void cb710_dump_regs(struct cb710_chip *chip, unsigned select)
+{
+	if (!(select & CB710_DUMP_REGS_MASK))
+		select = CB710_DUMP_REGS_ALL;
+	if (!(select & CB710_DUMP_ACCESS_MASK))
+		select |= CB710_DUMP_ACCESS_8;
+
+	if (select & CB710_DUMP_ACCESS_32)
+		cb710_read_and_dump_regs_32(chip, select);
+	if (select & CB710_DUMP_ACCESS_16)
+		cb710_read_and_dump_regs_16(chip, select);
+	if (select & CB710_DUMP_ACCESS_8)
+		cb710_read_and_dump_regs_8(chip, select);
+}
+EXPORT_SYMBOL_GPL(cb710_dump_regs);
+
diff --git a/drivers/misc/cb710/sgbuf2.c b/drivers/misc/cb710/sgbuf2.c
new file mode 100644
index 0000000..d38a7ac
--- /dev/null
+++ b/drivers/misc/cb710/sgbuf2.c
@@ -0,0 +1,150 @@
+/*
+ *  cb710/sgbuf2.c
+ *
+ *  Copyright by Michał Mirosław, 2008-2009
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/cb710.h>
+
+static bool sg_dwiter_next(struct sg_mapping_iter *miter)
+{
+	if (sg_miter_next(miter)) {
+		miter->consumed = 0;
+		return true;
+	} else
+		return false;
+}
+
+static bool sg_dwiter_is_at_end(struct sg_mapping_iter *miter)
+{
+	return miter->length == miter->consumed && !sg_dwiter_next(miter);
+}
+
+static uint32_t sg_dwiter_read_buffer(struct sg_mapping_iter *miter)
+{
+	size_t len, left = 4;
+	uint32_t data;
+	void *addr = &data;
+
+	do {
+		len = min(miter->length - miter->consumed, left);
+		memcpy(addr, miter->addr + miter->consumed, len);
+		miter->consumed += len;
+		left -= len;
+		if (!left)
+			return data;
+		addr += len;
+	} while (sg_dwiter_next(miter));
+
+	memset(addr, 0, left);
+	return data;
+}
+
+static inline bool needs_unaligned_copy(const void *ptr)
+{
+#ifdef HAVE_EFFICIENT_UNALIGNED_ACCESS
+	return false;
+#else
+	return ((ptr - NULL) & 3) != 0;
+#endif
+}
+
+static bool sg_dwiter_get_next_block(struct sg_mapping_iter *miter, uint32_t **ptr)
+{
+	size_t len;
+
+	if (sg_dwiter_is_at_end(miter))
+		return true;
+
+	len = miter->length - miter->consumed;
+
+	if (likely(len >= 4 && !needs_unaligned_copy(
+			miter->addr + miter->consumed))) {
+		*ptr = miter->addr + miter->consumed;
+		miter->consumed += 4;
+		return true;
+	}
+
+	return false;
+}
+
+/**
+ * cb710_sg_dwiter_read_next_block() - get next 32-bit word from sg buffer
+ * @miter: sg mapping iterator used for reading
+ *
+ * Description:
+ *   Returns 32-bit word starting at byte pointed to by @miter@
+ *   handling any alignment issues.  Bytes past the buffer's end
+ *   are not accessed (read) but are returned as zeroes.  @miter@
+ *   is advanced by 4 bytes or to the end of buffer whichever is
+ *   closer.
+ *
+ * Context:
+ *   Same requirements as in sg_miter_next().
+ *
+ * Returns:
+ *   32-bit word just read.
+ */
+uint32_t cb710_sg_dwiter_read_next_block(struct sg_mapping_iter *miter)
+{
+	uint32_t *ptr = NULL;
+
+	if (likely(sg_dwiter_get_next_block(miter, &ptr)))
+		return ptr ? *ptr : 0;
+
+	return sg_dwiter_read_buffer(miter);
+}
+EXPORT_SYMBOL_GPL(cb710_sg_dwiter_read_next_block);
+
+static void sg_dwiter_write_slow(struct sg_mapping_iter *miter, uint32_t data)
+{
+	size_t len, left = 4;
+	void *addr = &data;
+
+	do {
+		len = min(miter->length - miter->consumed, left);
+		memcpy(miter->addr, addr, len);
+		miter->consumed += len;
+		left -= len;
+		if (!left)
+			return;
+		addr += len;
+		flush_kernel_dcache_page(miter->page);
+	} while (sg_dwiter_next(miter));
+}
+
+/**
+ * cb710_sg_dwiter_write_next_block() - write next 32-bit word to sg buffer
+ * @miter: sg mapping iterator used for writing
+ *
+ * Description:
+ *   Writes 32-bit word starting at byte pointed to by @miter@
+ *   handling any alignment issues.  Bytes which would be written
+ *   past the buffer's end are silently discarded. @miter@ is
+ *   advanced by 4 bytes or to the end of buffer whichever is closer.
+ *
+ * Context:
+ *   Same requirements as in sg_miter_next().
+ */
+void cb710_sg_dwiter_write_next_block(struct sg_mapping_iter *miter, uint32_t data)
+{
+	uint32_t *ptr = NULL;
+
+	if (likely(sg_dwiter_get_next_block(miter, &ptr))) {
+		if (ptr)
+			*ptr = data;
+		else
+			return;
+	} else
+		sg_dwiter_write_slow(miter, data);
+
+	if (miter->length == miter->consumed)
+		flush_kernel_dcache_page(miter->page);
+}
+EXPORT_SYMBOL_GPL(cb710_sg_dwiter_write_next_block);
+