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drm/solomon: Add SSD130x OLED displays SPI support
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> Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be> Link: https://patchwork.freedesktop.org/patch/msgid/20220419214824.335075-6-javierm@redhat.com
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‎drivers/gpu/drm/solomon/Kconfig‎

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@@ -20,3 +20,12 @@ config DRM_SSD130X_I2C
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I2C bus.
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If M is selected the module will be called ssd130x-i2c.
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config DRM_SSD130X_SPI
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tristate "DRM support for Solomon SSD130X OLED displays (SPI bus)"
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depends on DRM_SSD130X && SPI
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select REGMAP
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help
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Say Y here if the SSD130x OLED display is connected via SPI bus.
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If M is selected the module will be called ssd130x-spi.

‎drivers/gpu/drm/solomon/Makefile‎

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obj-$(CONFIG_DRM_SSD130X) += ssd130x.o
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obj-$(CONFIG_DRM_SSD130X_I2C) += ssd130x-i2c.o
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obj-$(CONFIG_DRM_SSD130X_SPI) += ssd130x-spi.o

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

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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* DRM driver for Solomon SSD130X OLED displays (SPI bus)
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*
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* Copyright 2022 Red Hat Inc.
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* Authors: Javier Martinez Canillas <javierm@redhat.com>
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*/
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#include <linux/spi/spi.h>
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#include <linux/module.h>
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#include "ssd130x.h"
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#define DRIVER_NAME "ssd130x-spi"
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#define DRIVER_DESC "DRM driver for Solomon SSD130X OLED displays (SPI)"
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struct ssd130x_spi_transport {
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struct spi_device *spi;
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struct gpio_desc *dc;
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};
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static const struct regmap_config ssd130x_spi_regmap_config = {
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.reg_bits = 8,
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.val_bits = 8,
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};
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/*
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* The regmap bus .write handler, it is just a wrapper around spi_write()
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* but toggling the Data/Command control pin (D/C#). Since for 4-wire SPI
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* a D/C# pin is used, in contrast with I2C where a control byte is sent,
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* prior to every data byte, that contains a bit with the D/C# value.
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*
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* These control bytes are considered registers by the ssd130x core driver
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* and can be used by the ssd130x SPI driver to determine if the data sent
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* is for a command register or for the Graphic Display Data RAM (GDDRAM).
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*/
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static int ssd130x_spi_write(void *context, const void *data, size_t count)
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{
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struct ssd130x_spi_transport *t = context;
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struct spi_device *spi = t->spi;
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const u8 *reg = data;
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if (*reg == SSD130X_COMMAND)
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gpiod_set_value_cansleep(t->dc, 0);
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if (*reg == SSD130X_DATA)
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gpiod_set_value_cansleep(t->dc, 1);
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/* Remove control byte since is not used in a 4-wire SPI interface */
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return spi_write(spi, reg + 1, count - 1);
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}
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/* The ssd130x driver does not read registers but regmap expects a .read */
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static int ssd130x_spi_read(void *context, const void *reg, size_t reg_size,
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void *val, size_t val_size)
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{
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return -EOPNOTSUPP;
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}
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/*
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* A custom bus is needed due the special write that toggles a D/C# pin,
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* another option could be to just have a .reg_write() callback but that
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* will prevent to do data writes in bulk.
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*
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* Once the regmap API is extended to support defining a bulk write handler
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* in the struct regmap_config, this can be simplified and the bus dropped.
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*/
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static struct regmap_bus regmap_ssd130x_spi_bus = {
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.write = ssd130x_spi_write,
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.read = ssd130x_spi_read,
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};
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static int ssd130x_spi_probe(struct spi_device *spi)
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{
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struct ssd130x_spi_transport *t;
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struct ssd130x_device *ssd130x;
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struct regmap *regmap;
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struct gpio_desc *dc;
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struct device *dev = &spi->dev;
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dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_LOW);
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if (IS_ERR(dc))
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return dev_err_probe(dev, PTR_ERR(dc),
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"Failed to get dc gpio\n");
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t = devm_kzalloc(dev, sizeof(*t), GFP_KERNEL);
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if (!t)
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return dev_err_probe(dev, -ENOMEM,
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"Failed to allocate SPI transport data\n");
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t->spi = spi;
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t->dc = dc;
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regmap = devm_regmap_init(dev, &regmap_ssd130x_spi_bus, t,
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&ssd130x_spi_regmap_config);
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if (IS_ERR(regmap))
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return PTR_ERR(regmap);
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ssd130x = ssd130x_probe(dev, regmap);
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if (IS_ERR(ssd130x))
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return PTR_ERR(ssd130x);
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spi_set_drvdata(spi, ssd130x);
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return 0;
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}
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static void ssd130x_spi_remove(struct spi_device *spi)
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{
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struct ssd130x_device *ssd130x = spi_get_drvdata(spi);
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ssd130x_remove(ssd130x);
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}
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static void ssd130x_spi_shutdown(struct spi_device *spi)
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{
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struct ssd130x_device *ssd130x = spi_get_drvdata(spi);
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ssd130x_shutdown(ssd130x);
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}
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static const struct of_device_id ssd130x_of_match[] = {
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{
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.compatible = "sinowealth,sh1106",
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.data = &ssd130x_variants[SH1106_ID],
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},
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{
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.compatible = "solomon,ssd1305",
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.data = &ssd130x_variants[SSD1305_ID],
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},
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{
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.compatible = "solomon,ssd1306",
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.data = &ssd130x_variants[SSD1306_ID],
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},
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{
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.compatible = "solomon,ssd1307",
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.data = &ssd130x_variants[SSD1307_ID],
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},
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{
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.compatible = "solomon,ssd1309",
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.data = &ssd130x_variants[SSD1309_ID],
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},
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{ /* sentinel */ }
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};
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MODULE_DEVICE_TABLE(of, ssd130x_of_match);
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/*
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* The SPI core always reports a MODALIAS uevent of the form "spi:<dev>", even
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* if the device was registered via OF. This means that the module will not be
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* auto loaded, unless it contains an alias that matches the MODALIAS reported.
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*
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* To workaround this issue, add a SPI device ID table. Even when this should
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* not be needed for this driver to match the registered SPI devices.
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*/
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static const struct spi_device_id ssd130x_spi_table[] = {
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{ "sh1106", SH1106_ID },
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{ "ssd1305", SSD1305_ID },
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{ "ssd1306", SSD1306_ID },
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{ "ssd1307", SSD1307_ID },
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{ "ssd1309", SSD1309_ID },
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{ /* sentinel */ }
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};
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MODULE_DEVICE_TABLE(spi, ssd130x_spi_table);
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static struct spi_driver ssd130x_spi_driver = {
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.driver = {
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.name = DRIVER_NAME,
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.of_match_table = ssd130x_of_match,
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},
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.probe = ssd130x_spi_probe,
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.remove = ssd130x_spi_remove,
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.shutdown = ssd130x_spi_shutdown,
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};
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module_spi_driver(ssd130x_spi_driver);
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MODULE_DESCRIPTION(DRIVER_DESC);
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MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
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MODULE_LICENSE("GPL");
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MODULE_IMPORT_NS(DRM_SSD130X);

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