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

From: Sam Ravnborg
Date: Fri Oct 16 2020 - 16:07:43 EST

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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@xxxxx>

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.

> + 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@xxxxx>");
> +MODULE_DESCRIPTION("HiMax HX8837 Display Controller Driver");
> +MODULE_LICENSE("GPL");
> --
> 2.26.2
>
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