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authorCyrille Pitchen <cyrille.pitchen@atmel.com>2016-02-03 16:26:46 +0300
committerBrian Norris <computersforpeace@gmail.com>2016-02-12 22:35:13 +0300
commit3b5394a3ccffbfa1d1d448d48742853a862822c4 (patch)
treed167eb2fb40d1a6d652e07f459f5b9dd824fc5ae /drivers/mtd
parentc08266794926a9f6c2940e8585fbcbdc51caa7ed (diff)
downloadlinux-3b5394a3ccffbfa1d1d448d48742853a862822c4.tar.xz
mtd: spi-nor: remove micron_quad_enable()
This patch remove the micron_quad_enable() function which force the Quad SPI mode. However, once this mode is enabled, the Micron memory expect ALL commands to use the SPI 4-4-4 protocol. Hence a failure does occur when calling spi_nor_wait_till_ready() right after the update of the Enhanced Volatile Configuration Register (EVCR) in the micron_quad_enable() as the SPI controller driver is not aware about the protocol change. Since there is almost no performance increase using Fast Read 4-4-4 commands instead of Fast Read 1-1-4 commands, we rather keep on using the Extended SPI mode than enabling the Quad SPI mode. Let's take the example of the pretty standard use of 8 dummy cycles during Fast Read operations on 64KB erase sectors: Fast Read 1-1-4 requires 8 cycles for the command, then 24 cycles for the 3byte address followed by 8 dummy clock cycles and finally 65536*2 cycles for the read data; so 131112 clock cycles. On the other hand the Fast Read 4-4-4 would require 2 cycles for the command, then 6 cycles for the 3byte address followed by 8 dummy clock cycles and finally 65536*2 cycles for the read data. So 131088 clock cycles. The theorical bandwidth increase is 0.0%. Now using Fast Read operations on 512byte pages: Fast Read 1-1-4 needs 8+24+8+(512*2) = 1064 clock cycles whereas Fast Read 4-4-4 would requires 2+6+8+(512*2) = 1040 clock cycles. Hence the theorical bandwidth increase is 2.3%. Consecutive reads for non sequential pages is not a relevant use case so The Quad SPI mode is not worth it. mtd_speedtest seems to confirm these figures. Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com> Fixes: 548cd3ab54da ("mtd: spi-nor: Add quad I/O support for Micron SPI NOR") Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Diffstat (limited to 'drivers/mtd')
-rw-r--r--drivers/mtd/spi-nor/spi-nor.c46
1 files changed, 1 insertions, 45 deletions
diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
index 13e07ce3cebe..999b3ce51779 100644
--- a/drivers/mtd/spi-nor/spi-nor.c
+++ b/drivers/mtd/spi-nor/spi-nor.c
@@ -1101,45 +1101,6 @@ static int spansion_quad_enable(struct spi_nor *nor)
return 0;
}
-static int micron_quad_enable(struct spi_nor *nor)
-{
- int ret;
- u8 val;
-
- ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
- if (ret < 0) {
- dev_err(nor->dev, "error %d reading EVCR\n", ret);
- return ret;
- }
-
- write_enable(nor);
-
- /* set EVCR, enable quad I/O */
- nor->cmd_buf[0] = val & ~EVCR_QUAD_EN_MICRON;
- ret = nor->write_reg(nor, SPINOR_OP_WD_EVCR, nor->cmd_buf, 1);
- if (ret < 0) {
- dev_err(nor->dev, "error while writing EVCR register\n");
- return ret;
- }
-
- ret = spi_nor_wait_till_ready(nor);
- if (ret)
- return ret;
-
- /* read EVCR and check it */
- ret = nor->read_reg(nor, SPINOR_OP_RD_EVCR, &val, 1);
- if (ret < 0) {
- dev_err(nor->dev, "error %d reading EVCR\n", ret);
- return ret;
- }
- if (val & EVCR_QUAD_EN_MICRON) {
- dev_err(nor->dev, "Micron EVCR Quad bit not clear\n");
- return -EINVAL;
- }
-
- return 0;
-}
-
static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
{
int status;
@@ -1153,12 +1114,7 @@ static int set_quad_mode(struct spi_nor *nor, const struct flash_info *info)
}
return status;
case SNOR_MFR_MICRON:
- status = micron_quad_enable(nor);
- if (status) {
- dev_err(nor->dev, "Micron quad-read not enabled\n");
- return -EINVAL;
- }
- return status;
+ return 0;
default:
status = spansion_quad_enable(nor);
if (status) {