Title: [8976] trunk: Add SPI MODE_0/MODE_2 Warning:
- Revision
- 8976
- Author
- hennerich
- Date
- 2010-07-06 09:57:12 -0400 (Tue, 06 Jul 2010)
Log Message
Add SPI MODE_0/MODE_2 Warning:
With the Blackfin on-chip SPI peripheral, there is some logic tied to
the CPHA bit whether the Slave Select Line is controlled by hardware (CPHA=0) or
controlled by software (CPHA=1). However, the Linux SPI bus driver
assumes that the Slave Select being asserted during the entire SPI transfer.
Modified Paths
Added Paths
Diff
Modified: trunk/Documentation/blackfin/00-INDEX (8975 => 8976)
--- trunk/Documentation/blackfin/00-INDEX 2010-07-06 13:01:06 UTC (rev 8975)
+++ trunk/Documentation/blackfin/00-INDEX 2010-07-06 13:57:12 UTC (rev 8976)
@@ -1,5 +1,8 @@
00-INDEX
- This file
-bfin-gpio-note.txt
+bfin-gpio-notes.txt
- Notes in developing/using bfin-gpio driver.
+
+bfin-spi-notes.txt
+ - Notes for using bfin spi bus driver.
Added: trunk/Documentation/blackfin/bfin-spi-notes.txt (0 => 8976)
--- trunk/Documentation/blackfin/bfin-spi-notes.txt (rev 0)
+++ trunk/Documentation/blackfin/bfin-spi-notes.txt 2010-07-06 13:57:12 UTC (rev 8976)
@@ -0,0 +1,13 @@
+SPI Chip Select behavior:
+
+With the Blackfin on-chip SPI peripheral, there is some logic tied to the CPHA
+bit whether the Slave Select Line is controlled by hardware (CPHA=0) or
+controlled by software (CPHA=1). However, the Linux SPI bus driver assumes that
+the Slave Select being asserted during the entire SPI transfer.
+
+In most cases you can utilize SPI MODE_3 instead of MODE_0 to work-around this
+behavior. If your SPI slave device in question requires SPI MODE_0 or MODE_2
+timing, you can utilize the GPIO controlled SPI Slave Select option instead.
+
+You can even use the same pin whose peripheral role is a SSEL,
+but use it as a GPIO instead.
Modified: trunk/drivers/spi/spi_bfin5xx.c (8975 => 8976)
--- trunk/drivers/spi/spi_bfin5xx.c 2010-07-06 13:01:06 UTC (rev 8975)
+++ trunk/drivers/spi/spi_bfin5xx.c 2010-07-06 13:57:12 UTC (rev 8976)
@@ -1149,10 +1149,11 @@
chip->baud = hz_to_spi_baud(spi->max_speed_hz);
chip->chip_select_num = spi->chip_select;
if (chip->chip_select_num < MAX_CTRL_CS) {
- if (!(spi->mode & SPI_CPHA)) {
- dev_err(&spi->dev, "please use a GPIO as chipselect while CPHA is 0\n");
- goto error;
- }
+ if (!(spi->mode & SPI_CPHA))
+ dev_warn(&spi->dev, "Warning: SPI CPHA not set:"
+ " Slave Select not under software control!\n"
+ " See Documentation/blackfin/bfin-spi-notes.txt");
+
chip->flag = (1 << spi->chip_select) << 8;
} else
chip->cs_gpio = chip->chip_select_num - MAX_CTRL_CS;
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