[PATCH v2 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength property

[PATCH v2 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength property

[Alexander Stein]

This property is for optimizing output voltage impedance and is
specific to each board. It overwrites the default set by the flash
device. Various flash devices support different impedances.

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
---
Changes in v2:
* Updated the property description and the commit message accordingly

 Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
index ed590d7c6e37..4c3c506a8853 100644
--- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
+++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
@@ -72,6 +72,14 @@ properties:
       be used on such systems, to denote the absence of a reliable reset
       mechanism.
 
+  output-driver-strength:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Output driver strength in ohms which optimizes the impedance at Vcc/2
+      output voltage. This property overwrites the default set by the flash
+      device. This is board specific and should be determined by the
+      manufacturer. Various flash devices support different impedances.
+
   label: true
 
   partitions:
-- 
2.25.1

[PATCH v2 2/2] mtd: spi-nor: micron-st: Add support for output-driver-strength for MT25Q

[Alexander Stein]

MT25Q[UL] Micron flashes support this by the Bits [2:0] in the Enhanced
Volatile Configuration Register.
Checked datasheet:
- mt25t-qljs-L512-xBA-xxT.pdf

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
---
Changes in v2:
* Various format fixes
* Apply property only to MT25Q devices (e.g. N25Q devices support a
 different set of impedances)
* Use spi_nor_spimem_setup_op() before issuing a command
* Add more return code checking
* Add a warning if setting drive strength fails at some point
* Use GENMASK()

 drivers/mtd/spi-nor/micron-st.c | 152 ++++++++++++++++++++++++++++++--
 1 file changed, 146 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/spi-nor/micron-st.c b/drivers/mtd/spi-nor/micron-st.c
index c224e59820a1..492805a5a278 100644
--- a/drivers/mtd/spi-nor/micron-st.c
+++ b/drivers/mtd/spi-nor/micron-st.c
@@ -16,6 +16,11 @@
 #define SPINOR_MT_OCT_DTR	0xe7	/* Enable Octal DTR. */
 #define SPINOR_MT_EXSPI		0xff	/* Enable Extended SPI (default) */
 
+struct micron_drive_strength {
+	u32 ohms;
+	u8 val;
+};
+
 static int spi_nor_micron_octal_dtr_enable(struct spi_nor *nor, bool enable)
 {
 	struct spi_mem_op op;
@@ -118,6 +123,135 @@ static struct spi_nor_fixups mt35xu512aba_fixups = {
 	.post_sfdp = mt35xu512aba_post_sfdp_fixup,
 };
 
+/*
+ * Read Micron enhanced volatile configuration register
+ * Return negative if error occurred or configuration register value
+ */
+static int micron_read_evcr(struct spi_nor *nor)
+{
+	int ret;
+
+	if (nor->spimem) {
+		struct spi_mem_op op =
+			SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_RD_EVCR, 1),
+				   SPI_MEM_OP_NO_ADDR,
+				   SPI_MEM_OP_NO_DUMMY,
+				   SPI_MEM_OP_DATA_IN(1, nor->bouncebuf, 1));
+
+		spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
+
+		ret = spi_mem_exec_op(nor->spimem, &op);
+	} else {
+		ret = nor->controller_ops->read_reg(nor, SPINOR_OP_RD_EVCR,
+						    nor->bouncebuf, 1);
+	}
+
+	if (ret < 0) {
+		dev_err(nor->dev, "error %d reading EVCR\n", ret);
+		return ret;
+	}
+
+	return nor->bouncebuf[0];
+}
+
+/*
+ * Write Micron enhanced volatile configuration register
+ * Return negative if error occurred or configuration register value
+ */
+static int micron_write_evcr(struct spi_nor *nor, u8 evcr)
+{
+	int ret;
+
+	nor->bouncebuf[0] = evcr;
+
+	ret = spi_nor_write_enable(nor);
+	if (ret)
+		return ret;
+
+	if (nor->spimem) {
+		struct spi_mem_op op =
+			SPI_MEM_OP(SPI_MEM_OP_CMD(SPINOR_OP_WD_EVCR, 1),
+				   SPI_MEM_OP_NO_ADDR,
+				   SPI_MEM_OP_NO_DUMMY,
+				   SPI_MEM_OP_DATA_OUT(1, nor->bouncebuf, 1));
+
+		spi_nor_spimem_setup_op(nor, &op, nor->reg_proto);
+
+		return spi_mem_exec_op(nor->spimem, &op);
+	}
+
+	return nor->controller_ops->write_reg(nor, SPINOR_OP_WD_EVCR,
+					      nor->bouncebuf, 1);
+}
+
+/*
+ * Supported values from Enahanced Volatile COnfiguration Register (Bits 2:0)
+ */
+static const struct micron_drive_strength drive_strength_data[] = {
+	{ .ohms = 90, .val = 1 },
+	{ .ohms = 45, .val = 3 },
+	{ .ohms = 20, .val = 5 },
+	{ .ohms = 30, .val = 7 },
+};
+
+static const struct micron_drive_strength *micron_st_find_drive_strength_entry(u32 ohms)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(drive_strength_data); i++) {
+		if (ohms == drive_strength_data[i].ohms)
+			return &drive_strength_data[i];
+	}
+	return NULL;
+}
+
+static void mt25q_post_sfdp(struct spi_nor *nor)
+{
+	struct device_node *np = spi_nor_get_flash_node(nor);
+	u32 ohms;
+
+	if (!np)
+		return;
+
+	if (!of_property_read_u32(np, "output-driver-strength", &ohms)) {
+		struct micron_drive_strength const *entry =
+			micron_st_find_drive_strength_entry(ohms);
+
+		if (entry) {
+			int evcrr;
+			int ret;
+			u8 evcr;
+
+			evcrr = micron_read_evcr(nor);
+			if (evcrr < 0) {
+				dev_warn(nor->dev,
+					 "Reading EVCR failed: %d\n",
+					 evcrr);
+				return;
+			}
+
+			evcr = (u8)(evcrr & GENMASK(7, 3)) | entry->val;
+
+			ret = micron_write_evcr(nor, evcr);
+			if (ret)
+				dev_warn(nor->dev,
+					 "Setting EVCR failed: %d\n",
+					 ret);
+
+			dev_dbg(nor->dev, "%s: EVCR 0x%x\n", __func__,
+				(u32)micron_read_evcr(nor));
+		} else {
+			dev_warn(nor->dev,
+				"Invalid output-driver-strength property specified: %u",
+				ohms);
+		}
+	}
+}
+
+static struct spi_nor_fixups mt25q_fixups = {
+	.post_sfdp = mt25q_post_sfdp,
+};
+
 static const struct flash_info micron_parts[] = {
 	{ "mt35xu512aba", INFO(0x2c5b1a, 0, 128 * 1024, 512,
 			       SECT_4K | USE_FSR | SPI_NOR_OCTAL_READ |
@@ -149,25 +283,29 @@ static const struct flash_info st_parts[] = {
 			      SECT_4K | USE_FSR | SPI_NOR_QUAD_READ) },
 	{ "mt25ql256a",  INFO6(0x20ba19, 0x104400, 64 * 1024,  512,
 			       SECT_4K | USE_FSR | SPI_NOR_DUAL_READ |
-			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES) },
+			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES)
+	  .fixups = &mt25q_fixups },
 	{ "n25q256a",    INFO(0x20ba19, 0, 64 * 1024,  512, SECT_4K |
 			      USE_FSR | SPI_NOR_DUAL_READ |
 			      SPI_NOR_QUAD_READ) },
 	{ "mt25qu256a",  INFO6(0x20bb19, 0x104400, 64 * 1024,  512,
 			       SECT_4K | USE_FSR | SPI_NOR_DUAL_READ |
-			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES) },
+			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES)
+	  .fixups = &mt25q_fixups },
 	{ "n25q256ax1",  INFO(0x20bb19, 0, 64 * 1024,  512,
 			      SECT_4K | USE_FSR | SPI_NOR_QUAD_READ) },
 	{ "mt25ql512a",  INFO6(0x20ba20, 0x104400, 64 * 1024, 1024,
 			       SECT_4K | USE_FSR | SPI_NOR_DUAL_READ |
-			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES) },
+			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES)
+	  .fixups = &mt25q_fixups },
 	{ "n25q512ax3",  INFO(0x20ba20, 0, 64 * 1024, 1024,
 			      SECT_4K | USE_FSR | SPI_NOR_QUAD_READ |
 			      SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB |
 			      SPI_NOR_4BIT_BP | SPI_NOR_BP3_SR_BIT6) },
 	{ "mt25qu512a",  INFO6(0x20bb20, 0x104400, 64 * 1024, 1024,
 			       SECT_4K | USE_FSR | SPI_NOR_DUAL_READ |
-			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES) },
+			       SPI_NOR_QUAD_READ | SPI_NOR_4B_OPCODES)
+	  .fixups = &mt25q_fixups },
 	{ "n25q512a",    INFO(0x20bb20, 0, 64 * 1024, 1024,
 			      SECT_4K | USE_FSR | SPI_NOR_QUAD_READ |
 			      SPI_NOR_HAS_LOCK | SPI_NOR_HAS_TB |
@@ -182,10 +320,12 @@ static const struct flash_info st_parts[] = {
 			      NO_CHIP_ERASE) },
 	{ "mt25ql02g",   INFO(0x20ba22, 0, 64 * 1024, 4096,
 			      SECT_4K | USE_FSR | SPI_NOR_QUAD_READ |
-			      NO_CHIP_ERASE) },
+			      NO_CHIP_ERASE)
+	  .fixups = &mt25q_fixups },
 	{ "mt25qu02g",   INFO(0x20bb22, 0, 64 * 1024, 4096,
 			      SECT_4K | USE_FSR | SPI_NOR_DUAL_READ |
-			      SPI_NOR_QUAD_READ | NO_CHIP_ERASE) },
+			      SPI_NOR_QUAD_READ | NO_CHIP_ERASE)
+	  .fixups = &mt25q_fixups },
 
 	{ "m25p05",  INFO(0x202010,  0,  32 * 1024,   2, 0) },
 	{ "m25p10",  INFO(0x202011,  0,  32 * 1024,   4, 0) },
-- 
2.25.1

Re: [PATCH v2 1/2] dt-bindings: mtd: spi-nor: Add output-driver-strength property

[Michael Walle]

Am 2021-10-12 08:17, schrieb Alexander Stein:
> This property is for optimizing output voltage impedance and is
> specific to each board. It overwrites the default set by the flash
> device. Various flash devices support different impedances.
> 
> Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---
> Changes in v2:
> * Updated the property description and the commit message accordingly
> 
>  Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> index ed590d7c6e37..4c3c506a8853 100644
> --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.yaml
> @@ -72,6 +72,14 @@ properties:
>        be used on such systems, to denote the absence of a reliable 
> reset
>        mechanism.
> 
> +  output-driver-strength:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      Output driver strength in ohms which optimizes the impedance at 
> Vcc/2
> +      output voltage. This property overwrites the default set by the 
> flash
> +      device. This is board specific and should be determined by the
> +      manufacturer. Various flash devices support different 
> impedances.

Mh, this seems to be very tailored to this flash chip. Eg. the "Vcc/2", 
is
this something specific to this flash or is this some kind of common 
usage?
For example, Winbond flashes specifies the output driver strength in 
percent.
Settings are 25%, 50%, 75%, 100% there.

I'd have to ask a hardware guy, if one could convert between these two
representations of the driver strength.

Rob, do you know how is this case ususally handled? Can there be 
different
properties, like:

output-driver-strength-ohms
output-driver-strength-percent

or similar.

-michael