spi: gpio: Remove stale documentation part

The SPI GPIO driver doesn't support hard coded absolute GPIO numbers
anymore. However, it may still be instantiated from board files with
help of GPIO lookup tables or device properties. Neither of this is
covered by the old part of the documentation, it's the opposite, i.e.
old documentation pretend that antique approach still works. With all
this said, remove stale and confusing part of the documentation.

Signed-off-by: Andy Shevchenko <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Mark Brown <[email protected]>

Author: andy-shev

drivers/spi/spi-gpio.c

@@ -39,36 +39,8 @@ struct spi_gpio {
 
 /*----------------------------------------------------------------------*/
 
-/*
- * Because the overhead of going through four GPIO procedure calls
- * per transferred bit can make performance a problem, this code
- * is set up so that you can use it in either of two ways:
- *
- *   - The slow generic way:  set up platform_data to hold the GPIO
- *     numbers used for MISO/MOSI/SCK, and issue procedure calls for
- *     each of them.  This driver can handle several such busses.
- *
- *   - The quicker inlined way:  only helps with platform GPIO code
- *     that inlines operations for constant GPIOs.  This can give
- *     you tight (fast!) inner loops, but each such bus needs a
- *     new driver.  You'll define a new C file, with Makefile and
- *     Kconfig support; the C code can be a total of six lines:
- *
- *		#define DRIVER_NAME	"myboard_spi2"
- *		#define	SPI_MISO_GPIO	119
- *		#define	SPI_MOSI_GPIO	120
- *		#define	SPI_SCK_GPIO	121
- *		#define	SPI_N_CHIPSEL	4
- *		#include "spi-gpio.c"
- */
-
-#ifndef DRIVER_NAME
 #define DRIVER_NAME	"spi_gpio"
 
-#define GENERIC_BITBANG	/* vs tight inlines */
-
-#endif
-
 /*----------------------------------------------------------------------*/
 
 static inline struct spi_gpio *__pure
@@ -341,10 +313,9 @@ static int spi_gpio_probe_pdata(struct platform_device *pdev,
 	struct spi_gpio *spi_gpio = spi_controller_get_devdata(host);
 	int i;
 
-#ifdef GENERIC_BITBANG
 	if (!pdata || !pdata->num_chipselect)
 		return -ENODEV;
-#endif
+
 	/*
 	 * The host needs to think there is a chipselect even if not
 	 * connected
@@ -445,8 +416,6 @@ static int spi_gpio_probe(struct platform_device *pdev)
 	return devm_spi_register_controller(&pdev->dev, host);
 }
 
-MODULE_ALIAS("platform:" DRIVER_NAME);
-
 static const struct of_device_id spi_gpio_dt_ids[] = {
 	{ .compatible = "spi-gpio" },
 	{}
@@ -465,3 +434,4 @@ module_platform_driver(spi_gpio_driver);
 MODULE_DESCRIPTION("SPI host driver using generic bitbanged GPIO ");
 MODULE_AUTHOR("David Brownell");
 MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:" DRIVER_NAME);