drm/ssd130x: Use new regmap bulk write support to drop custom bus

Data writes for the ssd130x 4-wire SPI protocol need special handling, due
the Data/Command control (D/C) pin having to be toggled prior to the write.

The regmap API only allowed drivers to provide .reg_{read,write} callbacks
to do per register read/write, but didn't provide a way for drivers to do
the same for bulk read/writes.

For this reason, a custom regmap bus was used by the driver just to define
a bulk write callback that implements the D/C pin toggling. But the regmap
API has been extended to support defining bulk read/write handlers, so the
custom regmap bus is not needed anymore and could just be dropped.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220618174338.2253021-1-javierm@redhat.com

drivers/gpu/drm/solomon/ssd130x-spi.c

@@ -18,11 +18,6 @@ struct ssd130x_spi_transport {
 	struct gpio_desc *dc;
 };
 
-static const struct regmap_config ssd130x_spi_regmap_config = {
-	.reg_bits = 8,
-	.val_bits = 8,
-};
-
 /*
  * The regmap bus .write handler, it is just a wrapper around spi_write()
  * but toggling the Data/Command control pin (D/C#). Since for 4-wire SPI
@@ -56,17 +51,12 @@ static int ssd130x_spi_read(void *context, const void *reg, size_t reg_size,
 	return -EOPNOTSUPP;
 }
 
-/*
- * A custom bus is needed due the special write that toggles a D/C# pin,
- * another option could be to just have a .reg_write() callback but that
- * will prevent to do data writes in bulk.
- *
- * Once the regmap API is extended to support defining a bulk write handler
- * in the struct regmap_config, this can be simplified and the bus dropped.
- */
-static struct regmap_bus regmap_ssd130x_spi_bus = {
+static const struct regmap_config ssd130x_spi_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
 	.write = ssd130x_spi_write,
 	.read = ssd130x_spi_read,
+	.can_multi_write = true,
 };
 
 static int ssd130x_spi_probe(struct spi_device *spi)
@@ -90,8 +80,7 @@ static int ssd130x_spi_probe(struct spi_device *spi)
 	t->spi = spi;
 	t->dc = dc;
 
-	regmap = devm_regmap_init(dev, &regmap_ssd130x_spi_bus, t,
-				  &ssd130x_spi_regmap_config);
+	regmap = devm_regmap_init(dev, NULL, t, &ssd130x_spi_regmap_config);
 	if (IS_ERR(regmap))
 		return PTR_ERR(regmap);