drm/tiny: panel-mipi-dbi: Allow sharing the D/C GPIO

Displays that are connected to the same SPI bus may share the D/C GPIO.
Use GPIOD_FLAGS_BIT_NONEXCLUSIVE to allow access to the same GPIO for
multiple panel-mipi-dbi instances. Exclusive access to the GPIO during
transfers is ensured by the locking in drm_mipi_dbi.c.
Signed-off-by: Otto Pflüger <otto.pflueger@abscue.de>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230724065654.5269-3-otto.pflueger@abscue.de

drivers/gpu/drm/tiny/panel-mipi-dbi.c

@@ -307,7 +307,8 @@ static int panel_mipi_dbi_spi_probe(struct spi_device *spi)
 	if (IS_ERR(dbi->reset))
 		return dev_err_probe(dev, PTR_ERR(dbi->reset), "Failed to get GPIO 'reset'\n");
 
-	dc = devm_gpiod_get_optional(dev, "dc", GPIOD_OUT_LOW);
+	/* Multiple panels can share the "dc" GPIO, but only if they are on the same SPI bus! */
+	dc = devm_gpiod_get_optional(dev, "dc", GPIOD_OUT_LOW | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
 	if (IS_ERR(dc))
 		return dev_err_probe(dev, PTR_ERR(dc), "Failed to get GPIO 'dc'\n");