Re: [PATCH v2 2/2] drm/bridge: Introduce LT8912 DSI to HDMI bridge

From: Robert Foss
Date: Wed Feb 17 2021 - 12:36:12 EST

Hey Adrien,

Thanks for submitting this!

On Mon, 15 Feb 2021 at 00:31, Adrien Grassein <adrien.grassein@xxxxxxxxx> wrote:
>
> Lontium Lt8912 is a DSI to HDMI bridge.
>
> Signed-off-by: Adrien Grassein <adrien.grassein@xxxxxxxxx>
> ---
> MAINTAINERS | 1 +
> drivers/gpu/drm/bridge/Kconfig | 14 +
> drivers/gpu/drm/bridge/Makefile | 1 +
> drivers/gpu/drm/bridge/lontium-lt8912.c | 719 ++++++++++++++++++++++++
> 4 files changed, 735 insertions(+)
> create mode 100644 drivers/gpu/drm/bridge/lontium-lt8912.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f010b485aa7c..8b3d64b689c7 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10444,6 +10444,7 @@ LONTIUM LT8912 MIPI TO HDMI BRIDGE
> M: Adrien Grassein <adrien.grassein@xxxxxxxxx>
> S: Maintained
> F: Documentation/devicetree/bindings/display/bridge/lontium,lt8912.yaml
> +F: drivers/gpu/drm/bridge/lontium-lt8912.c
>
> LSILOGIC MPT FUSION DRIVERS (FC/SAS/SPI)
> M: Sathya Prakash <sathya.prakash@xxxxxxxxxxxx>
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index e4110d6ca7b3..5b36d4b86e3c 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -48,6 +48,20 @@ config DRM_DISPLAY_CONNECTOR
> on ARM-based platforms. Saying Y here when this driver is not needed
> will not cause any issue.
>
> +config DRM_LONTIUM_LT8912
> + tristate "Lontium LT8912 DSI/HDMI bridge"
> + depends on OF
> + select DRM_PANEL_BRIDGE
> + select DRM_KMS_HELPER
> + select REGMAP_I2C
> + help
> + Driver for Lontium LT8912 DSI to HDMI bridge
> + chip driver.
> + Please say Y if you have such hardware.
> +
> + Say M here if you want to support this hardware as a module.
> + The module will be named "lontium-lt8912".
> +
> config DRM_LONTIUM_LT9611
> tristate "Lontium LT9611 DSI/HDMI bridge"
> select SND_SOC_HDMI_CODEC if SND_SOC
> diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> index 86e7acc76f8d..5a1b201cea1f 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -2,6 +2,7 @@
> obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
> obj-$(CONFIG_DRM_CHRONTEL_CH7033) += chrontel-ch7033.o
> obj-$(CONFIG_DRM_DISPLAY_CONNECTOR) += display-connector.o
> +obj-$(CONFIG_DRM_LONTIUM_LT8912) += lontium-lt8912.o
> obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o
> obj-$(CONFIG_DRM_LONTIUM_LT9611UXC) += lontium-lt9611uxc.o
> obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o
> diff --git a/drivers/gpu/drm/bridge/lontium-lt8912.c b/drivers/gpu/drm/bridge/lontium-lt8912.c
> new file mode 100644
> index 000000000000..d713d3365c3e
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/lontium-lt8912.c
> @@ -0,0 +1,719 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2018, The Linux Foundation. All rights reserved.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/delay.h>
> +#include <linux/i2c.h>
> +#include <linux/gpio.h>
> +#include <linux/of_gpio.h>
> +#include <linux/regmap.h>
> +
> +#include <drm/drm_probe_helper.h>
> +#include <drm/drm_atomic_helper.h>
> +#include <drm/drm_mipi_dsi.h>
> +#include <drm/drm_of.h>
> +
> +#include <video/videomode.h>
> +
> +#define I2C_MAIN 0
> +#define I2C_ADDR_MAIN 0x48
> +
> +#define I2C_CEC_DSI 1
> +#define I2C_ADDR_CEC_DSI 0x49
> +
> +#define I2C_MAX_IDX 2
> +
> +#define HPD_WORK_DELAY_MS 1000
> +
> +struct lt8912 {
> + struct device *dev;
> + struct drm_bridge bridge;
> + struct drm_connector connector;
> +
> + struct i2c_client *i2c_client[I2C_MAX_IDX];
> + struct regmap *regmap[I2C_MAX_IDX];
> +
> + struct device_node *host_node;
> + struct drm_bridge *hdmi_port;
> +
> + struct mipi_dsi_device *dsi;
> +
> + struct gpio_desc *gp_reset;
> +
> + struct videomode mode;
> +
> + u8 data_lanes;
> + bool is_power_on;
> + bool is_attached;
> +};
> +
> +static int lt8912_write_init_config(struct lt8912 *lt)
> +{

For the following register accesses it would be nice to see the
registers named and the value written to them documented. If you don't
have access to all of that information, not adding it is acceptable,
but it will make the driver harder to maintain & extend going forward.

So if possible, document registers in the same way it was done for lt9611 [1].

[1] https://github.com/torvalds/linux/blob/master/drivers/gpu/drm/bridge/lontium-lt9611.c#L444

> + const struct reg_sequence seq[] = {
> + /* Digital clock en*/
> + {0x08, 0xff},
> + {0x09, 0xff},
> + {0x0a, 0xff},
> + {0x0b, 0x7c},
> + {0x0c, 0xff},
> + {0x42, 0x04},
> +
> + /*Tx Analog*/
> + {0x31, 0xb1},
> + {0x32, 0xb1},
> + {0x33, 0x0e},
> + {0x37, 0x00},
> + {0x38, 0x22},
> + {0x60, 0x82},
> +
> + /*Cbus Analog*/
> + {0x39, 0x45},
> + {0x3a, 0x00},
> + {0x3b, 0x00},
> +
> + /*HDMI Pll Analog*/
> + {0x44, 0x31},
> + {0x55, 0x44},
> + {0x57, 0x01},
> + {0x5a, 0x02},
> +
> + /*MIPI Analog*/
> + {0x3e, 0xd6},
> + {0x3f, 0xd4},
> + {0x41, 0x3c},
> + {0xB2, 0x00},
> + };
> +
> + return regmap_multi_reg_write(lt->regmap[I2C_MAIN], seq, ARRAY_SIZE(seq));
> +}
> +
> +static int lt8912_write_mipi_basic_config(struct lt8912 *lt)
> +{
> + const struct reg_sequence seq[] = {
> + {0x12, 0x04},
> + {0x14, 0x00},
> + {0x15, 0x00},
> + {0x1a, 0x03},
> + {0x1b, 0x03},
> + };
> +
> + return regmap_multi_reg_write(lt->regmap[I2C_CEC_DSI], seq, ARRAY_SIZE(seq));
> +};
> +
> +static int lt8912_write_dds_config(struct lt8912 *lt)
> +{
> + const struct reg_sequence seq[] = {
> + {0x4e, 0xff},
> + {0x4f, 0x56},
> + {0x50, 0x69},
> + {0x51, 0x80},
> + {0x1f, 0x5e},
> + {0x20, 0x01},
> + {0x21, 0x2c},
> + {0x22, 0x01},
> + {0x23, 0xfa},
> + {0x24, 0x00},
> + {0x25, 0xc8},
> + {0x26, 0x00},
> + {0x27, 0x5e},
> + {0x28, 0x01},
> + {0x29, 0x2c},
> + {0x2a, 0x01},
> + {0x2b, 0xfa},
> + {0x2c, 0x00},
> + {0x2d, 0xc8},
> + {0x2e, 0x00},
> + {0x42, 0x64},
> + {0x43, 0x00},
> + {0x44, 0x04},
> + {0x45, 0x00},
> + {0x46, 0x59},
> + {0x47, 0x00},
> + {0x48, 0xf2},
> + {0x49, 0x06},
> + {0x4a, 0x00},
> + {0x4b, 0x72},
> + {0x4c, 0x45},
> + {0x4d, 0x00},
> + {0x52, 0x08},
> + {0x53, 0x00},
> + {0x54, 0xb2},
> + {0x55, 0x00},
> + {0x56, 0xe4},
> + {0x57, 0x0d},
> + {0x58, 0x00},
> + {0x59, 0xe4},
> + {0x5a, 0x8a},
> + {0x5b, 0x00},
> + {0x5c, 0x34},
> + {0x1e, 0x4f},
> + {0x51, 0x00},
> + };
> +
> + return regmap_multi_reg_write(lt->regmap[I2C_CEC_DSI], seq, ARRAY_SIZE(seq));
> +}
> +
> +static int lt8912_write_rxlogicres_config(struct lt8912 *lt)
> +{
> + int ret;
> +
> + ret = regmap_write(lt->regmap[I2C_MAIN], 0x03, 0x7f);
> + usleep_range(10000, 20000);
> + ret |= regmap_write(lt->regmap[I2C_MAIN], 0x03, 0xff);
> +
> + return ret;
> +};
> +
> +static int lt8912_write_lvds_config(struct lt8912 *lt)
> +{
> + const struct reg_sequence seq[] = {
> + {0x44, 0x30},
> + {0x51, 0x05},
> + {0x50, 0x24},
> + {0x51, 0x2d},
> + {0x52, 0x04},
> + {0x69, 0x0e},
> + {0x69, 0x8e},
> + {0x6a, 0x00},
> + {0x6c, 0xb8},
> + {0x6b, 0x51},
> + {0x04, 0xfb},
> + {0x04, 0xff},
> + {0x7f, 0x00},
> + {0xa8, 0x13},
> + {0x02, 0xf7},
> + {0x02, 0xff},
> + {0x03, 0xcf},
> + {0x03, 0xff},
> + };
> +
> + return regmap_multi_reg_write(lt->regmap[I2C_CEC_DSI], seq, ARRAY_SIZE(seq));
> +};
> +
> +static inline struct lt8912 *bridge_to_lt8912(struct drm_bridge *b)
> +{
> + return container_of(b, struct lt8912, bridge);
> +}
> +
> +static inline struct lt8912 *connector_to_lt8912(struct drm_connector *c)
> +{
> + return container_of(c, struct lt8912, connector);
> +}
> +
> +static const struct regmap_config lt8912_regmap_config = {
> + .reg_bits = 8,
> + .val_bits = 8,
> + .max_register = 0xff,
> +};
> +
> +static int lt8912_init_i2c(struct lt8912 *lt)
> +{
> + unsigned int i;
> + int ret;
> + struct i2c_board_info info[] = {
> + { I2C_BOARD_INFO("lt8912p0", I2C_ADDR_MAIN), },
> + { I2C_BOARD_INFO("lt8912p1", I2C_ADDR_CEC_DSI), },
> + };
> +
> + if (!lt)
> + return -ENODEV;
> +
> + for (i = 0; i < ARRAY_SIZE(info); i++) {
> + if (i > 0) {
> + lt->i2c_client[i] = i2c_new_dummy_device(lt->i2c_client[0]->adapter,
> + info[i].addr);

Bad indentation. Some of these bad indentations look ok for
tab-width=4, however tab-width=8 is what the style guide dictates.

> + if (!lt->i2c_client[i])
> + return -ENODEV;
> + }
> + lt->regmap[i] = devm_regmap_init_i2c(lt->i2c_client[i],
> + &lt8912_regmap_config);

Bad indentation.

> + if (IS_ERR(lt->regmap[i])) {
> + ret = PTR_ERR(lt->regmap[i]);
> + return ret;
> + }
> + }
> + return 0;
> +}
> +
> +static int lt8912_free_i2c(struct lt8912 *lt)
> +{
> + unsigned int i;
> +
> + for (i = 1; i < I2C_MAX_IDX; i++)
> + i2c_unregister_device(lt->i2c_client[i]);
> +
> + return 0;
> +}
> +
> +static int lt8912_hard_power_on(struct lt8912 *lt)
> +{
> + gpiod_set_value_cansleep(lt->gp_reset, 0);
> + msleep(20);
> +
> + return 0;
> +}
> +
> +static void lt8912_hard_power_off(struct lt8912 *lt)
> +{
> + gpiod_set_value_cansleep(lt->gp_reset, 1);
> + msleep(20);
> + lt->is_power_on = false;
> +}
> +
> +static int lt8912_video_setup(struct lt8912 *lt)
> +{
> + u32 hactive, h_total, hpw, hfp, hbp;
> + u32 vactive, v_total, vpw, vfp, vbp;
> + u8 settle = 0x08;
> + int ret;
> +
> + if (!lt)
> + return -EINVAL;
> +
> + hactive = lt->mode.hactive;
> + hfp = lt->mode.hfront_porch;
> + hpw = lt->mode.hsync_len;
> + hbp = lt->mode.hback_porch;
> + h_total = hactive + hfp + hpw + hbp;
> +
> + vactive = lt->mode.vactive;
> + vfp = lt->mode.vfront_porch;
> + vpw = lt->mode.vsync_len;
> + vbp = lt->mode.vback_porch;
> + v_total = vactive + vfp + vpw + vbp;
> +
> + if (vactive <= 600)
> + settle = 0x04;
> + else if (vactive == 1080)
> + settle = 0x0a;
> +
> + ret = regmap_write(lt->regmap[I2C_CEC_DSI], 0x10, 0x01);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x11, settle);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x18, hpw);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x19, vpw);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x1c, hactive & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x1d, hactive >> 8);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x2f, 0x0c);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x34, h_total & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x35, h_total >> 8);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x36, v_total & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x37, v_total >> 8);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x38, vbp & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x39, vbp >> 8);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x3a, vfp & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x3b, vfp >> 8);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x3c, hbp & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x3d, hbp >> 8);
> +
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x3e, hfp & 0xff);
> + ret |= regmap_write(lt->regmap[I2C_CEC_DSI], 0x3f, hfp >> 8);
> +
> + return ret;
> +}
> +
> +static int lt8912_soft_power_on(struct lt8912 *lt)
> +{
> + if (!lt->is_power_on) {
> + u32 lanes = lt->data_lanes;
> +
> + lt8912_write_init_config(lt);
> + regmap_write(lt->regmap[I2C_CEC_DSI], 0x13, lanes & 3);
> +
> + lt8912_write_mipi_basic_config(lt);
> +
> + lt->is_power_on = true;
> + }
> +
> + return 0;
> +}
> +
> +static int lt8912_video_on(struct lt8912 *lt)
> +{
> + int ret;
> +
> + ret = lt8912_video_setup(lt);
> + if (ret < 0)
> + goto end;
> +
> + ret = lt8912_write_dds_config(lt);
> + if (ret < 0)
> + goto end;
> +
> + ret = lt8912_write_rxlogicres_config(lt);
> + if (ret < 0)
> + goto end;
> +
> + ret = lt8912_write_lvds_config(lt);
> + if (ret < 0)
> + goto end;
> +
> +end:
> + return ret;
> +}
> +
> +static enum drm_connector_status
> +lt8912_connector_detect(struct drm_connector *connector, bool force)
> +{
> + struct lt8912 *lt = connector_to_lt8912(connector);
> +
> + return drm_bridge_detect(lt->hdmi_port);
> +}
> +
> +static const struct drm_connector_funcs lt8912_connector_funcs = {
> + .detect = lt8912_connector_detect,
> + .fill_modes = drm_helper_probe_single_connector_modes,
> + .destroy = drm_connector_cleanup,
> + .reset = drm_atomic_helper_connector_reset,
> + .atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> + .atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> +};
> +
> +static enum drm_mode_status
> +lt8912_connector_mode_valid(struct drm_connector *connector,
> + struct drm_display_mode *mode)
> +{
> + if (mode->clock > 150000)
> + return MODE_CLOCK_HIGH;
> +
> + if (mode->hdisplay > 1920)
> + return MODE_BAD_HVALUE;
> +
> + if (mode->vdisplay > 1080)
> + return MODE_BAD_VVALUE;
> +
> + return MODE_OK;
> +}
> +
> +static int lt8912_connector_get_modes(struct drm_connector *connector)
> +{
> + struct edid *edid;
> + int ret, num = 0;
> + struct lt8912 *lt = connector_to_lt8912(connector);
> + u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> +
> + edid = drm_bridge_get_edid(lt->hdmi_port, connector);

Memory leak, edid is never free'd.

> + if (edid) {
> + drm_connector_update_edid_property(connector, edid);
> + num = drm_add_edid_modes(connector, edid);
> + } else
> + return ret;
> +
> + ret = drm_display_info_set_bus_formats(&connector->display_info,
> + &bus_format, 1);

Bad indentation.

> + if (ret)
> + return ret;
> +
> + return num;
> +}
> +
> +static const struct drm_connector_helper_funcs lt8912_connector_helper_funcs = {
> + .get_modes = lt8912_connector_get_modes,
> + .mode_valid = lt8912_connector_mode_valid,
> +};
> +
> +static void lt8912_bridge_mode_set(struct drm_bridge *bridge,
> + const struct drm_display_mode *mode,
> + const struct drm_display_mode *adj)
> +{
> + struct lt8912 *lt = bridge_to_lt8912(bridge);
> +
> + drm_display_mode_to_videomode(adj, &lt->mode);
> +}
> +
> +static void lt8912_bridge_enable(struct drm_bridge *bridge)
> +{
> + struct lt8912 *lt = bridge_to_lt8912(bridge);
> +
> + lt8912_video_on(lt);
> +}
> +
> +static int lt8912_attach_dsi(struct lt8912 *lt)
> +{
> + struct device *dev = lt->dev;
> + struct mipi_dsi_host *host;
> + struct mipi_dsi_device *dsi;
> + int ret = -1;
> + const struct mipi_dsi_device_info info = { .type = "lt8912",
> + .channel = 0,
> + .node = NULL,
> + };
> +
> + host = of_find_mipi_dsi_host_by_node(lt->host_node);
> + if (!host) {
> + dev_err(dev, "failed to find dsi host\n");
> + return -EPROBE_DEFER;
> + }
> +
> + dsi = mipi_dsi_device_register_full(host, &info);
> + if (IS_ERR(dsi)) {
> + ret = PTR_ERR(dsi);
> + dev_err(dev, "failed to create dsi device (%d)\n", ret);
> + goto err_dsi_device;
> + }
> +
> + lt->dsi = dsi;
> +
> + dsi->lanes = lt->data_lanes;
> + dsi->format = MIPI_DSI_FMT_RGB888;
> +
> + dsi->mode_flags = MIPI_DSI_MODE_VIDEO |
> + MIPI_DSI_MODE_VIDEO_BURST |
> + MIPI_DSI_MODE_LPM |
> + MIPI_DSI_MODE_EOT_PACKET;

Maybe align the 3 last lines with where the 1st one starts.

> +
> + ret = mipi_dsi_attach(dsi);
> + if (ret < 0) {
> + dev_err(dev, "failed to attach dsi to host\n");
> + goto err_dsi_attach;
> + }
> +
> + return 0;
> +
> +err_dsi_attach:
> + mipi_dsi_device_unregister(dsi);
> +err_dsi_device:
> + return ret;
> +}
> +
> +static void lt8912_detach_dsi(struct lt8912 *lt)
> +{
> + mipi_dsi_detach(lt->dsi);
> + mipi_dsi_device_unregister(lt->dsi);
> +}
> +
> +static int lt8912_bridge_init(struct drm_bridge *bridge)
> +{
> + int ret;
> + struct lt8912 *lt = bridge_to_lt8912(bridge);
> + struct drm_connector *connector = &lt->connector;
> +
> +
> + if (lt->hdmi_port->ops & DRM_BRIDGE_OP_DETECT) {
> + connector->polled = DRM_CONNECTOR_POLL_HPD;
> + } else {
> + connector->polled = DRM_CONNECTOR_POLL_CONNECT |
> + DRM_CONNECTOR_POLL_DISCONNECT;

Bad indentation.

> + }
> +
> +
> + ret = drm_connector_init(bridge->dev, connector,
> + &lt8912_connector_funcs,
> + lt->hdmi_port->type);
> + if (ret)
> + goto exit;
> +
> + drm_connector_helper_add(connector, &lt8912_connector_helper_funcs);
> +
> + connector->dpms = DRM_MODE_DPMS_OFF;
> + drm_connector_attach_encoder(connector, bridge->encoder);
> +
> +
> + ret = lt8912_hard_power_on(lt);
> + if (ret)
> + goto exit;
> +
> + ret = lt8912_soft_power_on(lt);
> +
> +exit:
> + return ret;
> +}
> +
> +static int lt8912_bridge_attach(struct drm_bridge *bridge,
> + enum drm_bridge_attach_flags flags)

Bad indentation.

> +{
> + struct lt8912 *lt = bridge_to_lt8912(bridge);
> + int ret;
> +
> + /* No need to check the return of this function */
> + drm_bridge_attach(lt->bridge.encoder,
> + lt->hdmi_port,
> + &lt->bridge,
> + flags);

Bad indentation.

> +
> + if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)) {
> + ret = lt8912_bridge_init(bridge);
> + if (ret) {
> + dev_err(lt->dev, "Failed to init bridge ! (%d)\n", ret);
> + return ret;
> + }
> + }
> +
> + ret = lt8912_attach_dsi(lt);
> + if (ret)
> + return ret;
> +
> + lt->is_attached = true;
> +
> + return ret;
> +}
> +
> +static void lt8912_bridge_detach(struct drm_bridge *bridge)
> +{
> + struct lt8912 *lt = bridge_to_lt8912(bridge);
> +
> + if (lt->is_attached) {
> + lt8912_detach_dsi(lt);
> + lt8912_hard_power_off(lt);
> + }
> +}
> +
> +static const struct drm_bridge_funcs lt8912_bridge_funcs = {
> + .attach = lt8912_bridge_attach,
> + .detach = lt8912_bridge_detach,
> + .mode_set = lt8912_bridge_mode_set,
> + .enable = lt8912_bridge_enable,

Have a look at the documentation around in drm_bridge_funcs[1], some
additional functions have to be implemented. I think you can look at
lt9611[2] & lt9611uxc[3] for inspiration.

[1] https://dri.freedesktop.org/docs/drm/gpu/drm-kms-helpers.html#bridge-operations
[2] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/bridge/lontium-lt9611.c#L947
[3] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/bridge/lontium-lt9611uxc.c#L542


> +};
> +
> +static int lt8912_parse_dt(struct lt8912 *lt)
> +{
> + struct gpio_desc *gp_reset;
> + struct device *dev = lt->dev;
> + int ret = 0;
> + struct device_node *port_node;
> + struct device_node *endpoint;
> +
> + gp_reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH);
> + if (IS_ERR(gp_reset)) {
> + ret = PTR_ERR(gp_reset);
> + if (ret != -EPROBE_DEFER)
> + dev_err(dev, "Failed to get reset gpio: %d\n", ret);
> + return ret;
> + }
> + lt->gp_reset = gp_reset;
> +
> +
> + endpoint = of_graph_get_endpoint_by_regs(dev->of_node, 0, -1);
> + if (IS_ERR(endpoint)) {
> + ret = PTR_ERR(endpoint);
> + goto end;
> + }
> +
> + lt->data_lanes = of_property_count_u32_elems(endpoint, "data-lanes");
> + of_node_put(endpoint);
> +
> + lt->host_node = of_graph_get_remote_node(dev->of_node, 0, -1);
> + if (!lt->host_node) {
> + dev_err(lt->dev, "%s: Failed to get remote port\n", __func__);
> + ret = -ENODEV;
> + goto end;
> + }
> +
> + port_node = of_graph_get_remote_node(dev->of_node, 1, -1);
> + if (!port_node) {
> + dev_err(lt->dev, "%s: Failed to get connector port\n", __func__);
> + ret = -ENODEV;
> + goto err_free_host_node;
> + }
> +
> + lt->hdmi_port = of_drm_find_bridge(port_node);
> + if (IS_ERR(lt->hdmi_port)) {
> + dev_err(lt->dev, "%s: Failed to get hdmi port\n", __func__);
> + ret = PTR_ERR(lt->hdmi_port);
> + of_node_put(lt->host_node);
> + goto end;
> + }
> +
> + if (!of_device_is_compatible(port_node, "hdmi-connector")) {
> + dev_err(lt->dev, "%s: Failed to get hdmi port\n", __func__);
> + ret = -EINVAL;
> + }
> +
> + of_node_put(port_node);
> +
> +end:
> + return ret;
> +
> +err_free_host_node:
> + of_node_put(lt->host_node);
> + return ret;
> +}
> +
> +static int lt8912_put_dt(struct lt8912 *lt)
> +{
> + of_node_put(lt->host_node);
> + return 0;
> +}
> +
> +static int lt8912_probe(struct i2c_client *client,
> + const struct i2c_device_id *id)
> +{
> + static struct lt8912 *lt;
> + int ret = 0;
> + struct device *dev = &client->dev;
> +
> + lt = devm_kzalloc(dev, sizeof(struct lt8912), GFP_KERNEL);
> + if (!lt)
> + return -ENOMEM;
> +
> + lt->dev = dev;
> + lt->i2c_client[0] = client;

The i2c_client that is created from the DT address and passed into
lt8912_probe will be overwritten by the i2c clients created in
lt8912_init_i2c before it is ever used.

A related issue is that this device has two I2C addresses, which
doesn't fit super neatly into the I2C driver model[1]. Since both
addresses can't be provided by the DT, method one doesn't fit this
driver. Method 2 doesn't fit well either, since the I2C bus isn't
internal to the device. And 3&4 are not applicable. I'd say the two
options are #1 splitting this driver, #2 keeping it like it is. I'm
leaning towards #2 since both addresses correspond to a physical chip.

[1] https://www.kernel.org/doc/html/latest/i2c/instantiating-devices.html

> +
> + ret = lt8912_parse_dt(lt);
> + if (ret)
> + goto err_dt_parse;
> +
> + ret = lt8912_init_i2c(lt);
> + if (ret)
> + goto err_i2c;
> +
> + i2c_set_clientdata(client, lt);
> +
> + lt->bridge.funcs = &lt8912_bridge_funcs;
> + lt->bridge.of_node = dev->of_node;
> + drm_bridge_add(&lt->bridge);
> +
> + return 0;
> +
> +err_i2c:
> + lt8912_put_dt(lt);
> +err_dt_parse:
> + return ret;
> +}
> +
> +static int lt8912_remove(struct i2c_client *client)
> +{
> + struct lt8912 *lt = i2c_get_clientdata(client);
> +
> + lt8912_bridge_detach(&lt->bridge);
> + drm_bridge_remove(&lt->bridge);
> + lt8912_free_i2c(lt);
> + lt8912_put_dt(lt);
> +
> + return 0;
> +}
> +
> +static const struct of_device_id lt8912_dt_match[] = {
> + {.compatible = "lontium,lt8912"},
> + {}
> +};
> +MODULE_DEVICE_TABLE(of, lt8912_dt_match);
> +
> +static const struct i2c_device_id lt8912_id[] = {
> + {"lt8912", 0},
> + {},
> +};
> +MODULE_DEVICE_TABLE(i2c, lt8912_id);
> +
> +static struct i2c_driver lt8912_i2c_driver = {
> + .driver = {
> + .name = "lt8912",
> + .of_match_table = lt8912_dt_match,
> + .owner = THIS_MODULE,

The .owner assignment is redundant as it is later re-assigned in[1].

module_i2c_driver -> i2c_add_driver -> i2c_register_driver

[1] https://elixir.bootlin.com/linux/latest/source/drivers/i2c/i2c-core-base.c#L1796

> + },
> + .probe = lt8912_probe,
> + .remove = lt8912_remove,
> + .id_table = lt8912_id,
> +};
> +module_i2c_driver(lt8912_i2c_driver);
> +
> +MODULE_AUTHOR("Adrien Grassein <adrien.grassein@xxxxxxxxx>");
> +MODULE_DESCRIPTION("lt8912 drm driver");
> +MODULE_LICENSE("GPL v2");
> --
> 2.25.1
>