spi: pxa2xx: Get rid of unused enable_loopback member

There is no user of the enable_loopback member in the struct pxa2xx_spi_chip.
Remote this legacy member completely.

The mentioned in the documentation the testing phase can be performed with
spidev_test tool.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211123192723.44537-3-andriy.shevchenko@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/spi/pxa2xx.rst

@@ -101,7 +101,6 @@ device. All fields are optional.
 	u8 rx_threshold;
 	u8 dma_burst_size;
 	u32 timeout;
-	u8 enable_loopback;
 	int gpio_cs;
   };
 
@@ -128,11 +127,6 @@ dependent on the SPI bus speed ("spi_board_info.max_speed_hz") and the specific
 slave device.  Please note that the PXA2xx SSP 1 does not support trailing byte
 timeouts and must busy-wait any trailing bytes.
 
-The "pxa2xx_spi_chip.enable_loopback" field is used to place the SSP porting
-into internal loopback mode.  In this mode the SSP controller internally
-connects the SSPTX pin to the SSPRX pin.  This is useful for initial setup
-testing.
-
 NOTE: the SPI driver cannot control the chip select if SSPFRM is used, so the
 chipselect is dropped after each spi_transfer.  Most devices need chip select
 asserted around the complete message. Use SSPFRM as a GPIO (through a descriptor)

drivers/spi/spi-pxa2xx.c

@@ -1289,7 +1289,6 @@ static int setup(struct spi_device *spi)
 	chip_info = spi->controller_data;
 
 	/* chip_info isn't always needed */
-	chip->cr1 = 0;
 	if (chip_info) {
 		if (chip_info->timeout)
 			chip->timeout = chip_info->timeout;
@@ -1300,9 +1299,9 @@ static int setup(struct spi_device *spi)
 		if (chip_info->rx_threshold)
 			rx_thres = chip_info->rx_threshold;
 		chip->dma_threshold = 0;
-		if (chip_info->enable_loopback)
-			chip->cr1 = SSCR1_LBM;
 	}
+
+	chip->cr1 = 0;
 	if (spi_controller_is_slave(drv_data->controller)) {
 		chip->cr1 |= SSCR1_SCFR;
 		chip->cr1 |= SSCR1_SCLKDIR;

include/linux/spi/pxa2xx_spi.h

@@ -42,7 +42,6 @@ struct pxa2xx_spi_chip {
 	u8 rx_threshold;
 	u8 dma_burst_size;
 	u32 timeout;
-	u8 enable_loopback;
 	int gpio_cs;
 };