Re: [PATCH v2 0/2] eeprom: at25: SPI transfer improvements

[Boris Brezillon <bbrezillon@xxxxxxxxxx>]

Hi Geert,

On Fri, 18 Jan 2019 15:05:23 +0100
Geert Uytterhoeven <geert+renesas@xxxxxxxxx> wrote:

> 	Hi all,
> 
> This patch series contains two improvements for the AT25 SPI EEPROM
> driver, related to SPI transfers.
> 
> Changes compared to v1:
>   - Merge "off" and "offset" into a single variable instead of just
>     killing the cast, as suggested by Arnd,
>   - Add Acked-by,
>   - Dropped "[PATCH 3/3] eeprom: at25: Split writes in two SPI transfers
>     to optimize DMA", as this is better implemented in the SPI
>     controller driver (cfr. e.g. "[v2 PATCH 2/2] spi: sh-msiof: Use DMA
>     if possible",
>     https://lore.kernel.org/linux-renesas-soc/1547803771-9564-2-git-send-email-na-hoan@xxxxxxxxxxx/)
> 
> Tested on a Renesas Ebisu development board with R-Car E3 using MSIOF
> and a 25LC040 EEPROM.

Did you consider converting this driver to spimem? Looks like the
protocol used to communicate with the memory resembles the one used on
SPI NANDs/NORs and fits pretty well in the spi_mem_op representation.

By doing this conversion you'd allow people to connect an AT25 EEPROM
to an advanced SPI controller that does not support regular SPI
transfers and you wouldn't have to forge SPI messages manually.

Here is a patch (only compile tested) doing that. The diffstat is not in
favor of this conversion, but I find the resulting code cleaner and more
future proof.

Regards,

Boris

drivers/misc/eeprom/at25.c | 302 ++++++++++++++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 198 insertions(+), 104 deletions(-)

--->8---
diff --git a/drivers/misc/eeprom/at25.c b/drivers/misc/eeprom/at25.c
index 99de6939cd5a..b9697a27e69b 100644
--- a/drivers/misc/eeprom/at25.c
+++ b/drivers/misc/eeprom/at25.c
@@ -17,7 +17,7 @@
 #include <linux/sched.h>
 
 #include <linux/nvmem-provider.h>
-#include <linux/spi/spi.h>
+#include <linux/spi/spi-mem.h>
 #include <linux/spi/eeprom.h>
 #include <linux/property.h>
 
@@ -29,12 +29,17 @@
  */
 
 struct at25_data {
-	struct spi_device	*spi;
+	struct spi_mem		*spimem;
 	struct mutex		lock;
 	struct spi_eeprom	chip;
 	unsigned		addrlen;
 	struct nvmem_config	nvmem_config;
 	struct nvmem_device	*nvmem;
+	void			*scratchbuf;
+	struct {
+		struct spi_mem_dirmap_desc *rdesc[2];
+		struct spi_mem_dirmap_desc *wdesc[2];
+	} dirmap;
 };
 
 #define	AT25_WREN	0x06		/* latch the write enable */
@@ -63,17 +68,117 @@ struct at25_data {
 
 #define	io_limit	PAGE_SIZE	/* bytes */
 
+static void at25_destroy_dirmaps(struct at25_data *at25)
+{
+	if (at25->dirmap.rdesc[0])
+		spi_mem_dirmap_destroy(at25->dirmap.rdesc[0]);
+	if (at25->dirmap.rdesc[1])
+		spi_mem_dirmap_destroy(at25->dirmap.rdesc[1]);
+	if (at25->dirmap.wdesc[0])
+		spi_mem_dirmap_destroy(at25->dirmap.wdesc[0]);
+	if (at25->dirmap.wdesc[1])
+		spi_mem_dirmap_destroy(at25->dirmap.wdesc[1]);
+}
+
+static int at25_create_dirmaps(struct at25_data *at25)
+{
+	struct spi_mem_dirmap_info info = {
+		.op_tmpl = SPI_MEM_OP(SPI_MEM_OP_CMD(AT25_READ, 1),
+				      SPI_MEM_OP_ADDR(at25->addrlen, 0, 1),
+				      SPI_MEM_OP_NO_DUMMY,
+				      SPI_MEM_OP_DATA_IN(0, NULL, 1)),
+		.offset = 0,
+		.length = at25->chip.byte_len,
+	};
+	struct spi_mem_dirmap_desc *desc;
+	int ret;
+
+	if (info.length > 1 << at25->addrlen)
+		info.length = at25->chip.byte_len;
+
+	desc = spi_mem_dirmap_create(at25->spimem, &info);
+	if (IS_ERR(desc))
+		return PTR_ERR(desc);
+
+	at25->dirmap.rdesc[0] = desc;
+
+	info.op_tmpl.cmd.opcode = AT25_WRITE;
+	info.op_tmpl.data.dir = SPI_MEM_DATA_OUT;
+
+	desc = spi_mem_dirmap_create(at25->spimem, &info);
+	if (IS_ERR(desc)) {
+		ret = PTR_ERR(desc);
+		goto err_destroy_dirmaps;
+	}
+
+	at25->dirmap.wdesc[0] = desc;
+
+	if (!(at25->chip.flags & EE_INSTR_BIT3_IS_ADDR))
+		return 0;
+
+	info.offset = 256;
+	info.length = at25->chip.byte_len - 256;
+	info.op_tmpl.cmd.opcode = AT25_READ | AT25_INSTR_BIT3;
+	info.op_tmpl.data.dir = SPI_MEM_DATA_IN;
+
+	desc = spi_mem_dirmap_create(at25->spimem, &info);
+	if (IS_ERR(desc)) {
+		ret = PTR_ERR(desc);
+		goto err_destroy_dirmaps;
+	}
+
+	at25->dirmap.rdesc[1] = desc;
+
+	info.op_tmpl.cmd.opcode = AT25_WRITE | AT25_INSTR_BIT3;
+	info.op_tmpl.data.dir = SPI_MEM_DATA_OUT;
+
+	desc = spi_mem_dirmap_create(at25->spimem, &info);
+	if (IS_ERR(desc)) {
+		ret = PTR_ERR(desc);
+		goto err_destroy_dirmaps;
+	}
+
+	at25->dirmap.wdesc[1] = desc;
+
+	return 0;
+
+err_destroy_dirmaps:
+	at25_destroy_dirmaps(at25);
+
+	return ret;
+}
+
+static int at25_rdsr(struct at25_data *at25)
+{
+	struct spi_mem_op op = SPI_MEM_OP(SPI_MEM_OP_CMD(AT25_RDSR, 1),
+					  SPI_MEM_OP_NO_ADDR,
+					  SPI_MEM_OP_NO_DUMMY,
+					  SPI_MEM_OP_DATA_IN(1, at25->scratchbuf, 1));
+	int ret;
+
+	ret = spi_mem_exec_op(at25->spimem, &op);
+	if (ret)
+		return ret;
+
+	return *((u8 *)at25->scratchbuf);
+}
+
+static int at25_wren(struct at25_data *at25)
+{
+	struct spi_mem_op op = SPI_MEM_OP(SPI_MEM_OP_CMD(AT25_WREN, 1),
+					  SPI_MEM_OP_NO_ADDR,
+					  SPI_MEM_OP_NO_DUMMY,
+					  SPI_MEM_OP_NO_DATA);
+
+	return spi_mem_exec_op(at25->spimem, &op);
+}
+
 static int at25_ee_read(void *priv, unsigned int offset,
 			void *val, size_t count)
 {
+	struct spi_mem_dirmap_desc *desc;
 	struct at25_data *at25 = priv;
-	char *buf = val;
-	u8			command[EE_MAXADDRLEN + 1];
-	u8			*cp;
 	ssize_t			status;
-	struct spi_transfer	t[2];
-	struct spi_message	m;
-	u8			instr;
 
 	if (unlikely(offset >= at25->chip.byte_len))
 		return -EINVAL;
@@ -82,37 +187,10 @@ static int at25_ee_read(void *priv, unsigned int offset,
 	if (unlikely(!count))
 		return -EINVAL;
 
-	cp = command;
-
-	instr = AT25_READ;
-	if (at25->chip.flags & EE_INSTR_BIT3_IS_ADDR)
-		if (offset >= (1U << (at25->addrlen * 8)))
-			instr |= AT25_INSTR_BIT3;
-	*cp++ = instr;
-
-	/* 8/16/24-bit address is written MSB first */
-	switch (at25->addrlen) {
-	default:	/* case 3 */
-		*cp++ = offset >> 16;
-		/* fall through */
-	case 2:
-		*cp++ = offset >> 8;
-		/* fall through */
-	case 1:
-	case 0:	/* can't happen: for better codegen */
-		*cp++ = offset >> 0;
-	}
-
-	spi_message_init(&m);
-	memset(t, 0, sizeof(t));
-
-	t[0].tx_buf = command;
-	t[0].len = at25->addrlen + 1;
-	spi_message_add_tail(&t[0], &m);
-
-	t[1].rx_buf = buf;
-	t[1].len = count;
-	spi_message_add_tail(&t[1], &m);
+	if (at25->chip.flags & EE_INSTR_BIT3_IS_ADDR && offset > 255)
+		desc = at25->dirmap.rdesc[1];
+	else
+		desc = at25->dirmap.rdesc[0];
 
 	mutex_lock(&at25->lock);
 
@@ -122,8 +200,8 @@ static int at25_ee_read(void *priv, unsigned int offset,
 	 * other devices on the bus need to be accessed regularly or
 	 * this chip is clocked very slowly
 	 */
-	status = spi_sync(at25->spi, &m);
-	dev_dbg(&at25->spi->dev, "read %zu bytes at %d --> %zd\n",
+	status = spi_mem_dirmap_read(desc, offset, count, val);
+	dev_dbg(&at25->spimem->spi->dev, "read %zu bytes at %d --> %zd\n",
 		count, offset, status);
 
 	mutex_unlock(&at25->lock);
@@ -149,7 +227,7 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
 	buf_size = at25->chip.page_size;
 	if (buf_size > io_limit)
 		buf_size = io_limit;
-	bounce = kmalloc(buf_size + at25->addrlen + 1, GFP_KERNEL);
+	bounce = kmalloc(buf_size, GFP_KERNEL);
 	if (!bounce)
 		return -ENOMEM;
 
@@ -158,47 +236,32 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
 	 */
 	mutex_lock(&at25->lock);
 	do {
+		struct spi_mem_dirmap_desc *desc;
 		unsigned long	timeout, retries;
 		unsigned	segment;
 		unsigned	offset = (unsigned) off;
-		u8		*cp = bounce;
 		int		sr;
-		u8		instr;
 
-		*cp = AT25_WREN;
-		status = spi_write(at25->spi, cp, 1);
+		status = at25_wren(at25);
 		if (status < 0) {
-			dev_dbg(&at25->spi->dev, "WREN --> %d\n", status);
+			dev_dbg(&at25->spimem->spi->dev, "WREN --> %d\n",
+				status);
 			break;
 		}
 
-		instr = AT25_WRITE;
-		if (at25->chip.flags & EE_INSTR_BIT3_IS_ADDR)
-			if (offset >= (1U << (at25->addrlen * 8)))
-				instr |= AT25_INSTR_BIT3;
-		*cp++ = instr;
-
-		/* 8/16/24-bit address is written MSB first */
-		switch (at25->addrlen) {
-		default:	/* case 3 */
-			*cp++ = offset >> 16;
-			/* fall through */
-		case 2:
-			*cp++ = offset >> 8;
-			/* fall through */
-		case 1:
-		case 0:	/* can't happen: for better codegen */
-			*cp++ = offset >> 0;
-		}
+		if (at25->chip.flags & EE_INSTR_BIT3_IS_ADDR && offset > 255)
+			desc = at25->dirmap.wdesc[1];
+		else
+			desc = at25->dirmap.wdesc[0];
 
 		/* Write as much of a page as we can */
 		segment = buf_size - (offset % buf_size);
 		if (segment > count)
 			segment = count;
-		memcpy(cp, buf, segment);
-		status = spi_write(at25->spi, bounce,
-				segment + at25->addrlen + 1);
-		dev_dbg(&at25->spi->dev, "write %u bytes at %u --> %d\n",
+		memcpy(bounce, buf, segment);
+		status = spi_mem_dirmap_write(desc, offset, segment, bounce);
+		dev_dbg(&at25->spimem->spi->dev,
+			"write %u bytes at %u --> %d\n",
 			segment, offset, status);
 		if (status < 0)
 			break;
@@ -211,10 +274,9 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
 		timeout = jiffies + msecs_to_jiffies(EE_TIMEOUT);
 		retries = 0;
 		do {
-
-			sr = spi_w8r8(at25->spi, AT25_RDSR);
+			sr = at25_rdsr(at25);
 			if (sr < 0 || (sr & AT25_SR_nRDY)) {
-				dev_dbg(&at25->spi->dev,
+				dev_dbg(&at25->spimem->spi->dev,
 					"rdsr --> %d (%02x)\n", sr, sr);
 				/* at HZ=100, this is sloooow */
 				msleep(1);
@@ -225,7 +287,7 @@ static int at25_ee_write(void *priv, unsigned int off, void *val, size_t count)
 		} while (retries++ < 3 || time_before_eq(jiffies, timeout));
 
 		if ((sr < 0) || (sr & AT25_SR_nRDY)) {
-			dev_err(&at25->spi->dev,
+			dev_err(&at25->spimem->spi->dev,
 				"write %u bytes offset %u, timeout after %u msecs\n",
 				segment, offset,
 				jiffies_to_msecs(jiffies -
@@ -304,7 +366,7 @@ static int at25_fw_to_chip(struct device *dev, struct spi_eeprom *chip)
 	return 0;
 }
 
-static int at25_probe(struct spi_device *spi)
+static int at25_probe(struct spi_mem *spimem)
 {
 	struct at25_data	*at25 = NULL;
 	struct spi_eeprom	chip;
@@ -313,12 +375,12 @@ static int at25_probe(struct spi_device *spi)
 	int			addrlen;
 
 	/* Chip description */
-	if (!spi->dev.platform_data) {
-		err = at25_fw_to_chip(&spi->dev, &chip);
+	if (!spimem->spi->dev.platform_data) {
+		err = at25_fw_to_chip(&spimem->spi->dev, &chip);
 		if (err)
 			return err;
 	} else
-		chip = *(struct spi_eeprom *)spi->dev.platform_data;
+		chip = *(struct spi_eeprom *)spimem->spi->dev.platform_data;
 
 	/* For now we only support 8/16/24 bit addressing */
 	if (chip.flags & EE_ADDR1)
@@ -328,37 +390,48 @@ static int at25_probe(struct spi_device *spi)
 	else if (chip.flags & EE_ADDR3)
 		addrlen = 3;
 	else {
-		dev_dbg(&spi->dev, "unsupported address type\n");
+		dev_dbg(&spimem->spi->dev, "unsupported address type\n");
 		return -EINVAL;
 	}
 
-	/* Ping the chip ... the status register is pretty portable,
-	 * unlike probing manufacturer IDs.  We do expect that system
-	 * firmware didn't write it in the past few milliseconds!
-	 */
-	sr = spi_w8r8(spi, AT25_RDSR);
-	if (sr < 0 || sr & AT25_SR_nRDY) {
-		dev_dbg(&spi->dev, "rdsr --> %d (%02x)\n", sr, sr);
-		return -ENXIO;
-	}
-
-	at25 = devm_kzalloc(&spi->dev, sizeof(struct at25_data), GFP_KERNEL);
+	at25 = devm_kzalloc(&spimem->spi->dev, sizeof(struct at25_data), GFP_KERNEL);
 	if (!at25)
 		return -ENOMEM;
 
 	mutex_init(&at25->lock);
 	at25->chip = chip;
-	at25->spi = spi;
-	spi_set_drvdata(spi, at25);
+	at25->spimem = spimem;
+	spi_mem_set_drvdata(spimem, at25);
 	at25->addrlen = addrlen;
 
-	at25->nvmem_config.name = dev_name(&spi->dev);
-	at25->nvmem_config.dev = &spi->dev;
+	/*
+	 * Can't be allocated with devm_kmalloc() because we need a DMA-safe
+	 * buffer.
+	 */
+	at25->scratchbuf = kmalloc(1, GFP_KERNEL);
+
+	/* Ping the chip ... the status register is pretty portable,
+	 * unlike probing manufacturer IDs.  We do expect that system
+	 * firmware didn't write it in the past few milliseconds!
+	 */
+	sr = at25_rdsr(at25);
+	if (sr < 0 || sr & AT25_SR_nRDY) {
+		dev_dbg(&spimem->spi->dev, "rdsr --> %d (%02x)\n", sr, sr);
+		err = -ENXIO;
+		goto err_free_scratchbuf;
+	}
+
+	err = at25_create_dirmaps(at25);
+	if (err)
+		goto err_free_scratchbuf;
+
+	at25->nvmem_config.name = dev_name(&spimem->spi->dev);
+	at25->nvmem_config.dev = &spimem->spi->dev;
 	at25->nvmem_config.read_only = chip.flags & EE_READONLY;
 	at25->nvmem_config.root_only = true;
 	at25->nvmem_config.owner = THIS_MODULE;
 	at25->nvmem_config.compat = true;
-	at25->nvmem_config.base_dev = &spi->dev;
+	at25->nvmem_config.base_dev = &spimem->spi->dev;
 	at25->nvmem_config.reg_read = at25_ee_read;
 	at25->nvmem_config.reg_write = at25_ee_write;
 	at25->nvmem_config.priv = at25;
@@ -366,17 +439,38 @@ static int at25_probe(struct spi_device *spi)
 	at25->nvmem_config.word_size = 1;
 	at25->nvmem_config.size = chip.byte_len;
 
-	at25->nvmem = devm_nvmem_register(&spi->dev, &at25->nvmem_config);
-	if (IS_ERR(at25->nvmem))
-		return PTR_ERR(at25->nvmem);
+	at25->nvmem = devm_nvmem_register(&spimem->spi->dev,
+					  &at25->nvmem_config);
+	if (IS_ERR(at25->nvmem)) {
+		err = PTR_ERR(at25->nvmem);
+		goto err_destroy_dirmaps;
+	}
 
-	dev_info(&spi->dev, "%d %s %s eeprom%s, pagesize %u\n",
+	dev_info(&spimem->spi->dev, "%d %s %s eeprom%s, pagesize %u\n",
 		(chip.byte_len < 1024) ? chip.byte_len : (chip.byte_len / 1024),
 		(chip.byte_len < 1024) ? "Byte" : "KByte",
 		at25->chip.name,
 		(chip.flags & EE_READONLY) ? " (readonly)" : "",
 		at25->chip.page_size);
 	return 0;
+
+err_destroy_dirmaps:
+	at25_destroy_dirmaps(at25);
+
+err_free_scratchbuf:
+	kfree(at25->scratchbuf);
+
+	return err;
+}
+
+static int at25_remove(struct spi_mem *spimem)
+{
+	struct at25_data *at25 = spi_mem_get_drvdata(spimem);
+
+	at25_destroy_dirmaps(at25);
+	kfree(at25->scratchbuf);
+
+	return 0;
 }
 
 /*-------------------------------------------------------------------------*/
@@ -387,15 +481,15 @@ static const struct of_device_id at25_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, at25_of_match);
 
-static struct spi_driver at25_driver = {
-	.driver = {
-		.name		= "at25",
+static struct spi_mem_driver at25_driver = {
+	.spidrv.driver = {
+		.name = "at25",
 		.of_match_table = at25_of_match,
 	},
-	.probe		= at25_probe,
+	.probe = at25_probe,
+	.remove = at25_remove,
 };
-
-module_spi_driver(at25_driver);
+module_spi_mem_driver(at25_driver);
 
 MODULE_DESCRIPTION("Driver for most SPI EEPROMs");
 MODULE_AUTHOR("David Brownell");