[PATCH v2 5/5] drm/solomon: Add SSD130x OLED displays SPI support

Javier Martinez Canillas
2022-04-11T21:13:22Z

The ssd130x driver only provides the core support for these devices but it
does not have any bus transport logic. Add a driver to interface over SPI.

There is a difference in the communication protocol when using 4-wire SPI
instead of I2C. For the latter, a control byte that contains a D/C# field
has to be sent. This field tells the controller whether the data has to be
written to the command register or to the graphics display data memory.

But for 4-wire SPI that control byte is not used, instead a real D/C# line
must be pulled HIGH for commands data and LOW for graphics display data.

For this reason the standard SPI regmap can't be used and a custom .write
bus handler is needed.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Acked-by: Mark Brown <broonie@kernel.org>
---

(no changes since v1)

drivers/gpu/drm/solomon/Kconfig | 9 ++
drivers/gpu/drm/solomon/Makefile | 1 +
drivers/gpu/drm/solomon/ssd130x-spi.c | 184 ++++++++++++++++++++++++++
3 files changed, 194 insertions(+)
create mode 100644 drivers/gpu/drm/solomon/ssd130x-spi.c

diff --git a/drivers/gpu/drm/solomon/Kconfig b/drivers/gpu/drm/solomon/Kconfig
index 8c0a0c788385..e170716d976b 100644
--- a/drivers/gpu/drm/solomon/Kconfig
+++ b/drivers/gpu/drm/solomon/Kconfig
@@ -20,3 +20,12 @@ config DRM_SSD130X_I2C
I2C bus.

If M is selected the module will be called ssd130x-i2c.
+
+config DRM_SSD130X_SPI
+ tristate "DRM support for Solomon SSD130X OLED displays (SPI bus)"
+ depends on DRM_SSD130X && SPI
+ select REGMAP
+ help
+ Say Y here if the SSD130x OLED display is connected via SPI bus.
+
+ If M is selected the module will be called ssd130x-spi.
diff --git a/drivers/gpu/drm/solomon/Makefile b/drivers/gpu/drm/solomon/Makefile
index 4bfc5acb0447..b5fc792257d7 100644
--- a/drivers/gpu/drm/solomon/Makefile
+++ b/drivers/gpu/drm/solomon/Makefile
@@ -1,2 +1,3 @@
obj-$(CONFIG_DRM_SSD130X) += ssd130x.o
obj-$(CONFIG_DRM_SSD130X_I2C) += ssd130x-i2c.o
+obj-$(CONFIG_DRM_SSD130X_SPI) += ssd130x-spi.o
diff --git a/drivers/gpu/drm/solomon/ssd130x-spi.c b/drivers/gpu/drm/solomon/ssd130x-spi.c
new file mode 100644
index 000000000000..b6fee66a0c01
--- /dev/null
+++ b/drivers/gpu/drm/solomon/ssd130x-spi.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * DRM driver for Solomon SSD130X OLED displays (SPI bus)
+ *
+ * Copyright 2022 Red Hat Inc.
+ * Authors: Javier Martinez Canillas <javierm@redhat.com>
+ */
+#include <linux/spi/spi.h>
+#include <linux/module.h>
+
+#include "ssd130x.h"
+
+#define DRIVER_NAME "ssd130x-spi"
+#define DRIVER_DESC "DRM driver for Solomon SSD130X OLED displays (SPI)"
+
+struct ssd130x_spi_transport {
+ struct spi_device *spi;
+ 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
+ * a D/C# pin is used, in contrast with I2C where a control byte is sent,
+ * prior to every data byte, that contains a bit with the D/C# value.
+ *
+ * These control bytes are considered registers by the ssd130x core driver
+ * and can be used by the ssd130x SPI driver to determine if the data sent
+ * is for a command register or for the Graphic Display Data RAM (GDDRAM).
+ */
+static int ssd130x_spi_write(void *context, const void *data, size_t count)
+{
+ struct ssd130x_spi_transport *t = context;
+ struct spi_device *spi = t->spi;
+ const u8 *reg = data;
+
+ if (*reg == SSD130X_COMMAND)
+ gpiod_set_value_cansleep(t->dc, 0);
+
+ if (*reg == SSD130X_DATA)
+ gpiod_set_value_cansleep(t->dc, 1);
+
+ /* Remove the control byte since is not used by the 4-wire SPI */
+ return spi_write(spi, ((u8 *)data) + 1, count - 1);
+}
+
+/* The ssd130x driver does not read registers but regmap expects a .read */
+static int ssd130x_spi_read(void *context, const void *reg, size_t reg_size,
+ void *val, size_t val_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 = {
+ .write = ssd130x_spi_write,
+ .read = ssd130x_spi_read,
+};
+
+static struct gpio_desc *ssd130x_spi_get_dc(struct device *dev)
+{
+ struct gpio_desc *dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_LOW);
+
+ if (IS_ERR(dc))
+ return ERR_PTR(dev_err_probe(dev, PTR_ERR(dc), "Failed to get dc gpio\n"));
+
+ return dc;
+}
+
+static int ssd130x_spi_probe(struct spi_device *spi)
+{
+ struct ssd130x_spi_transport *t;
+ struct ssd130x_device *ssd130x;
+ struct regmap *regmap;
+ struct device *dev = &spi->dev;
+
+ t = devm_kzalloc(dev, sizeof(*t), GFP_KERNEL);
+ if (!t)
+ return dev_err_probe(dev, -ENOMEM,
+ "Failed to allocate SPI transport data\n");
+
+ t->spi = spi;
+
+ t->dc = ssd130x_spi_get_dc(&spi->dev);
+ if (IS_ERR(t->dc))
+ return PTR_ERR(t->dc);
+
+ regmap = devm_regmap_init(dev, &regmap_ssd130x_spi_bus, t,
+ &ssd130x_spi_regmap_config);
+ if (IS_ERR(regmap))
+ return PTR_ERR(regmap);
+
+ ssd130x = ssd130x_probe(dev, regmap);
+ if (IS_ERR(ssd130x))
+ return PTR_ERR(ssd130x);
+
+ spi_set_drvdata(spi, ssd130x);
+
+ return 0;
+}
+
+static void ssd130x_spi_remove(struct spi_device *spi)
+{
+ struct ssd130x_device *ssd130x = spi_get_drvdata(spi);
+
+ ssd130x_remove(ssd130x);
+}
+
+static void ssd130x_spi_shutdown(struct spi_device *spi)
+{
+ struct ssd130x_device *ssd130x = spi_get_drvdata(spi);
+
+ ssd130x_shutdown(ssd130x);
+}
+
+static const struct of_device_id ssd130x_of_match[] = {
+ {
+ .compatible = "sinowealth,sh1106",
+ .data = (void *)SH1106_ID,
+ },
+ {
+ .compatible = "solomon,ssd1305",
+ .data = (void *)SSD1305_ID,
+ },
+ {
+ .compatible = "solomon,ssd1306",
+ .data = (void *)SSD1306_ID,
+ },
+ {
+ .compatible = "solomon,ssd1307",
+ .data = (void *)SSD1307_ID,
+ },
+ {
+ .compatible = "solomon,ssd1309",
+ .data = (void *)SSD1309_ID,
+ },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, ssd130x_of_match);
+
+/*
+ * The SPI core always reports a MODALIAS uevent of the form "spi:<dev>", even
+ * if the device was registered via OF. This means that the module will not be
+ * auto loaded, unless it contains an alias that matches the MODALIAS reported.
+ *
+ * To workaround this issue, add a SPI device ID table. Even when this should
+ * not be needed for this driver to match the registered SPI devices.
+ */
+static const struct spi_device_id ssd130x_spi_table[] = {
+ { "sh1106", SH1106_ID },
+ { "ssd1305", SSD1305_ID },
+ { "ssd1306", SSD1306_ID },
+ { "ssd1307", SSD1307_ID },
+ { "ssd1309", SSD1309_ID },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(spi, ssd130x_spi_table);
+
+static struct spi_driver ssd130x_spi_driver = {
+ .driver = {
+ .name = DRIVER_NAME,
+ .of_match_table = ssd130x_of_match,
+ },
+ .probe = ssd130x_spi_probe,
+ .remove = ssd130x_spi_remove,
+ .shutdown = ssd130x_spi_shutdown,
+};
+module_spi_driver(ssd130x_spi_driver);
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
+MODULE_LICENSE("GPL");
--
2.35.1