Re: [RESEND PATCH v5 2/2] drm/bridge: hx8837: add a Himax HX8837 display controller driver

Hello Sam,

On Fri, Oct 16, 2020 at 10:07:34PM +0200, Sam Ravnborg wrote:

Hi Lubomir.

On Sat, Sep 26, 2020 at 02:07:19AM +0200, Lubomir Rintel wrote:

...

Himax HX8837 is used to drive the LCD panel on OLPC platforms.

It controls the panel backlight and is able to refresh it when the LCD controller (and the rest of the plaform) is powered off.

It also converts regular RGB color data from the LCDC so that it looks reasonable on the OLPC LCD panel with a monochromatic layer on top of a layer that can either reflect light (b/w sunlight readable mode) or light pattern of red, green and blue pixels.

At this point, the driver is rather basic. The self-refresh mode is not supported. There's no way of independently controlling the color swizzling, antialiasing or b/w conversion, but it probably isn't too useful either.

There's another driver for the same hardware on OLPC XO-1.5 and XO-1.75 in drivers/staging/olpc_dcon. The display on that hardware doesn't utilize DRM, so this driver doesn't replace the other one yet.

Signed-off-by: Lubomir Rintel lkundrak@v3.sk

A little feedback follows.

Sam

...

---

Changes since v3:

• Added this patch, in place of a driver derived from drivers/staging/olpc_dcon. Compared to the previous one this implements the bare minimum, without the fancy stuff such as self-refresh that need more work/thinking.

drivers/gpu/drm/bridge/Kconfig | 13 ++ drivers/gpu/drm/bridge/Makefile | 1 + drivers/gpu/drm/bridge/himax-hx8837.c | 325 ++++++++++++++++++++++++++ 3 files changed, 339 insertions(+) create mode 100644 drivers/gpu/drm/bridge/himax-hx8837.c

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig index ef91646441b16..6a923dd56c1d5 100644 --- a/drivers/gpu/drm/bridge/Kconfig +++ b/drivers/gpu/drm/bridge/Kconfig @@ -48,6 +48,19 @@ config DRM_DISPLAY_CONNECTOR on ARM-based platforms. Saying Y here when this driver is not needed will not cause any issue.

+config DRM_HIMAX_HX8837

•    tristate "HiMax HX8837 OLPC Display Controller"
  

• depends on OF
• depends on OLPC || ARCH_MMP || COMPILE_TEST
• select DRM_KMS_HELPER

•    select BACKLIGHT_LCD_SUPPORT
  

•    select BACKLIGHT_CLASS_DEVICE
  

•    help
  

•      Enable support for HiMax HX8837 Display Controller as found in the
  

•      OLPC XO laptops.
  

•      If your laptop doesn't have green ears, say "N"
  

There is a mixture of tabs and spaces for indent - use tabs only (and tabs + 2 spaces for the help text).

...

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 2b3aff104e466..21f72df3260db 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_HIMAX_HX8837) += himax-hx8837.o

Please add in alphabetical order.

...

obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o obj-$(CONFIG_DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW) += megachips-stdpxxxx-ge-b850v3-fw.o diff --git a/drivers/gpu/drm/bridge/himax-hx8837.c b/drivers/gpu/drm/bridge/himax-hx8837.c new file mode 100644 index 0000000000000..1e97fcb8ce505 --- /dev/null +++ b/drivers/gpu/drm/bridge/himax-hx8837.c @@ -0,0 +1,325 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/*

• • HiMax HX8837 Display Controller Driver
• • Datasheet: http://wiki.laptop.org/images/0/09/DCON_datasheet_HX8837-A.pdf
• • Copyright (C) 2020 Lubomir Rintel
• */

+#include <linux/gpio/consumer.h> +#include <linux/module.h> +#include <linux/regmap.h>

+#include <drm/drm_atomic_helper.h> +#include <drm/drm_panel.h> +#include <drm/drm_bridge.h> +#include <drm/drm_of.h> +#include <drm/drm_print.h> +#include <drm/drm_probe_helper.h>

In blocks are good but please add them in alphabetical order.

...

+#define bridge_to_hx8837_priv(x) \

• container_of(x, struct hx8837_priv, bridge)

+/* DCON registers */ +enum {

• DCON_REG_ID = 0x00,
• DCON_REG_MODE = 0x01,
• DCON_REG_HRES = 0x02,
• DCON_REG_HTOTAL = 0x03,
• DCON_REG_HSYNC_WIDTH = 0x04,
• DCON_REG_VRES = 0x05,
• DCON_REG_VTOTAL = 0x06,
• DCON_REG_VSYNC_WIDTH = 0x07,
• DCON_REG_TIMEOUT = 0x08,
• DCON_REG_SCAN_INT = 0x09,
• DCON_REG_BRIGHT = 0x0a,
• DCON_REG_MEM_OPT_A = 0x41,
• DCON_REG_MEM_OPT_B = 0x42,

+};

+/* DCON_REG_MODE */ +enum {

• MODE_PASSTHRU = BIT(0),
• MODE_SLEEP = BIT(1),
• MODE_SLEEP_AUTO = BIT(2),
• MODE_BL_ENABLE = BIT(3),
• MODE_BLANK = BIT(4),
• MODE_CSWIZZLE = BIT(5),
• MODE_COL_AA = BIT(6),
• MODE_MONO_LUMA = BIT(7),
• MODE_SCAN_INT = BIT(8),
• MODE_CLOCKDIV = BIT(9),
• MODE_DEBUG = BIT(14),
• MODE_SELFTEST = BIT(15),

+};

+struct hx8837_priv {

• struct regmap *regmap;
• struct gpio_desc *load_gpio;
• struct drm_bridge *panel_bridge;
• struct drm_panel *panel;

No need for the panel pointer - use a local variable in the probe function

...

• struct drm_bridge bridge;

+};

+static int hx8837_bridge_attach(struct drm_bridge *bridge,

• 		enum drm_bridge_attach_flags flags)
  

+{

• struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
• return drm_bridge_attach(bridge->encoder, priv->panel_bridge,

• 		 bridge, flags);
  

+}

+static enum drm_mode_status hx8837_bridge_mode_valid(

• 		struct drm_bridge *bridge,
  

• 		const struct drm_display_info *info,
  

• 		const struct drm_display_mode *mode)
  

+{

• if (mode->hdisplay > 0xffff)

• return MODE_BAD_HVALUE;
  

• if (mode->htotal > 0xffff)

• return MODE_BAD_HVALUE;
  

• if (mode->hsync_start - mode->hdisplay > 0xff)

• return MODE_HBLANK_WIDE;
  

• if (mode->hsync_end - mode->hsync_start > 0xff)

• return MODE_HSYNC_WIDE;
  

• if (mode->vdisplay > 0xffff)

• return MODE_BAD_VVALUE;
  

• if (mode->vtotal > 0xffff)

• return MODE_BAD_VVALUE;
  

• if (mode->vsync_start - mode->vdisplay > 0xff)

• return MODE_VBLANK_WIDE;
  

• if (mode->vsync_end - mode->vsync_start > 0xff)

• return MODE_VSYNC_WIDE;
  

• return MODE_OK;

+}

+static void hx8837_bridge_disable(struct drm_bridge *bridge) +{

• struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
• int ret;
• ret = gpiod_direction_output(priv->load_gpio, 0);
• if (ret)

• DRM_ERROR("error enabling the dcon load: %d\n", ret);
  

The driver uses both dev_xxx() and DRM_XXX for logging. Please stick to one way to do logging - I prefer for bridge drivers the dev_* variants.

...

• ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,

• 			       MODE_PASSTHRU |
  

• 			       MODE_SLEEP,
  

• 			       MODE_PASSTHRU |
  

• 			       MODE_SLEEP);
  

• if (ret)

• DRM_ERROR("error disabling the dcon: %d\n", ret);
  

+}

+static void hx8837_bridge_enable(struct drm_bridge *bridge) +{

• struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
• int ret;
• ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,

• 			       MODE_PASSTHRU |
  

• 			       MODE_SLEEP |
  

• 			       MODE_SLEEP_AUTO |
  

• 			       MODE_BLANK |
  

• 			       MODE_SCAN_INT |
  

• 			       MODE_CLOCKDIV |
  

• 			       MODE_DEBUG |
  

• 			       MODE_SELFTEST,
  

• 			       MODE_PASSTHRU);
  

• if (ret)

• DRM_ERROR("error enabling the dcon: %d\n", ret);
  

• ret = gpiod_direction_output(priv->load_gpio, 1);
• if (ret)

• DRM_ERROR("error enabling the dcon load: %d\n", ret);
  

+}

+static void hx8837_bridge_mode_set(struct drm_bridge *bridge,

• 	   const struct drm_display_mode *mode,
  

• 	   const struct drm_display_mode *adjusted_mode)
  

+{

• struct hx8837_priv *priv = bridge_to_hx8837_priv(bridge);
• regmap_write(priv->regmap, DCON_REG_HRES, mode->hdisplay);
• regmap_write(priv->regmap, DCON_REG_HTOTAL, mode->htotal);
• regmap_write(priv->regmap, DCON_REG_HSYNC_WIDTH,

• 	(mode->hsync_start - mode->hdisplay) << 8 |
  

• 	(mode->hsync_end - mode->hsync_start));
  

• regmap_write(priv->regmap, DCON_REG_VRES, mode->vdisplay);
• regmap_write(priv->regmap, DCON_REG_VTOTAL, mode->vtotal);
• regmap_write(priv->regmap, DCON_REG_VSYNC_WIDTH,

• 	(mode->vsync_start - mode->vdisplay) << 8 |
  

• 	(mode->vsync_end - mode->vsync_start));
  

+}

+static const struct drm_bridge_funcs hx8837_bridge_funcs = {

• .attach = hx8837_bridge_attach,
• .mode_valid = hx8837_bridge_mode_valid,
• .disable = hx8837_bridge_disable,
• .enable = hx8837_bridge_enable,
• .mode_set = hx8837_bridge_mode_set,

+};

+static int hx8837_bl_update_status(struct backlight_device *bl) +{

• struct hx8837_priv *priv = bl_get_data(bl);
• unsigned int val;
• int ret;
• ret = regmap_update_bits(priv->regmap, DCON_REG_BRIGHT,

• 			       0x000f,
  

• 			       bl->props.brightness);
  

Use backlight_get_brightness() to get the brightness. This will also make sure 0 is returned when backlight is off so the logic a few lines down is correct.

I'm not sure I understand this one. I'm wondering if you could help me out with it before I follow up with v4.

Currently I read in the current brightness level in probe() (which prevents struct backlight_properties, below, from being const) and the nthe brightness is entirely in control of the driver via update_status().

What would I need get_brightness() for? We know that whatever the driver set is the current level. It doesn't seem to be called on backlight device registration so it doesn't make the readin in probe() unnecessary either.

...

• if (ret) {

• dev_err(&bl->dev, "error setting the backlight: %d\n", ret);
  

• return ret;
  

• }
• if (bl->props.brightness)

• val = MODE_CSWIZZLE | MODE_COL_AA;
  

• else

• val = MODE_MONO_LUMA;
  

• ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,

• 			       MODE_CSWIZZLE |
  

• 			       MODE_COL_AA |
  

• 			       MODE_MONO_LUMA,
  

• 			       val);
  

• if (ret) {

• dev_err(&bl->dev, "error setting color mode: %d\n", ret);
  

• return ret;
  

• }
• return 0;

+}

+static const struct backlight_ops hx8837_bl_ops = {

• .update_status = hx8837_bl_update_status,

+};

+static const struct regmap_config hx8837_regmap_config = {

• .reg_bits = 8,
• .val_bits = 16,
• .max_register = 0x4c,
• .val_format_endian = REGMAP_ENDIAN_LITTLE,

+};

+static int hx8837_probe(struct i2c_client *client,

• 	const struct i2c_device_id *id)
  

+{

• struct backlight_properties bl_props = {

• .type = BACKLIGHT_RAW,
  

• .max_brightness = 0xf,
  

• };

Make it const Maybe use a constant for the max value as it is also used as a mask later.

...

• struct device *dev = &client->dev;
• struct backlight_device *bl;
• struct hx8837_priv *priv;
• unsigned int val;
• int ret;
• priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
• if (!priv)

• return -ENOMEM;
  

• dev_set_drvdata(dev, priv);
• priv->load_gpio = devm_gpiod_get(dev, "load", GPIOD_ASIS);
• if (IS_ERR(priv->load_gpio))

• return PTR_ERR(priv->load_gpio);
  

• ret = drm_of_find_panel_or_bridge(dev->of_node, 1, -1,

• 			  &priv->panel, NULL);
  

• if (ret)

• return ret;
  

• if (priv->panel->backlight) {

• dev_err(dev, "the panel already has a backlight controller\n");
  

• return -ENODEV;
  

• }
• priv->panel_bridge = devm_drm_panel_bridge_add(dev, priv->panel);
• if (IS_ERR(priv->panel_bridge))

• return PTR_ERR(priv->panel_bridge);
  

• priv->regmap = devm_regmap_init_i2c(client, &hx8837_regmap_config);
• if (IS_ERR(priv->regmap)) {

• dev_err(dev, "regmap init failed\n");
  

• return PTR_ERR(priv->regmap);
  

• }
• ret = regmap_read(priv->regmap, DCON_REG_ID, &val);
• if (ret < 0) {

• dev_err(dev, "error reading the model id: %d\n", ret);
  

• return ret;
  

• }
• if ((val & 0xff00) != 0xdc00) {

• dev_err(dev, "the device is not a hx8837\n");
  

• return -ENODEV;
  

• }
• ret = regmap_read(priv->regmap, DCON_REG_BRIGHT, &val);
• if (ret < 0) {

• dev_err(&bl->dev, "error getting the backlight: %d\n", ret);
  

• return ret;
  

• }
• bl_props.brightness = val & 0xf;
• bl = devm_backlight_device_register(dev, dev_name(dev), dev, priv,

• 			    &hx8837_bl_ops, &bl_props);
  

• if (IS_ERR(bl)) {

• dev_err(dev, "failed to register backlight\n");
  

• return PTR_ERR(bl);
  

• }
• priv->panel->backlight = bl;
• INIT_LIST_HEAD(&priv->bridge.list);
• priv->bridge.funcs = &hx8837_bridge_funcs;
• priv->bridge.of_node = dev->of_node;
• drm_bridge_add(&priv->bridge);
• dev_info(dev, "HiMax HX8837 Display Controller Driver\n");
• return 0;

+}

+static int hx8837_remove(struct i2c_client *client) +{

• struct device *dev = &client->dev;
• struct hx8837_priv *priv = dev_get_drvdata(dev);
• drm_bridge_remove(&priv->bridge);

...

• priv->panel->backlight = NULL;

I cannot see why this is needed. IF this is needed we have a bug in the core stuff we need to fix.

...

• return 0;

+}

+static const struct of_device_id hx8837_dt_ids[] = {

• { .compatible = "himax,hx8837", },
• { }

We often see { /* sentinel */ }, in these cases.

...

+}; +MODULE_DEVICE_TABLE(of, hx8837_dt_ids);

+static const struct i2c_device_id hx8837_ids[] = {

• { "hx8837", 0 },
• { }

Likewise

...

+}; +MODULE_DEVICE_TABLE(i2c, hx8837_ids);

+static struct i2c_driver hx8837_driver = {

• .probe = hx8837_probe,
• .remove = hx8837_remove,
• .driver = {

• .name = "hx8837",
  

• .of_match_table = of_match_ptr(hx8837_dt_ids),
  

• },
• .id_table = hx8837_ids,

+};

+module_i2c_driver(hx8837_driver);

+MODULE_AUTHOR("Lubomir Rintel lkundrak@v3.sk"); +MODULE_DESCRIPTION("HiMax HX8837 Display Controller Driver"); +MODULE_LICENSE("GPL");

Thanks Lubo