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Date:   Sat, 31 Oct 2020 09:01:37 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Lubomir Rintel <lkundrak@...sk>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v6 2/2] drm/bridge: hx8837: add a Himax HX8837 display
 controller driver

Hi Lubomir.

On Fri, Oct 30, 2020 at 04:08:00AM +0100, 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@...sk>
> 
> ---
> Changes since v5:
> (All based on feedback from Sam Ravnborg)
> - Fix indentation in Kconfig
> - Sort #includes
> - Use a constant for max brightness instead of a literal
> - Remove struct drm_panel from priv data
> - Use dev_err() instead of DRM_ERROR
> - Replace direct use of backlight props.brightness with
>   backlight_get_brightness()
> - Document sentinels with { /* sentinel */ }
> - Remove unsetting of panel->backlight

Thanks, I missed a few things during the last round, so here is a few
more comments. Only very trivial things but lets get them fixed before
we add the driver to drm-misc-next.

	Sam

> 
> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index ef91646441b16..881780719af7c 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
Unknown symbol - "git grep BACKLIGHT_LCD_SUPPORT" only turned up one
unrelated hit.

> +	select BACKLIGHT_CLASS_DEVICE
Please use a depends - using select on a symbol with a prompt is always
wrong. Yeah, I know you then need to enable backlight to see this
driver. Sorry, but this is the best we can do now.
Many other drivers can cope with depends here.

> +	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"
I like this last comment :-)

> +
>  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
>  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..f472e16cc331d
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/himax-hx8837.c
> @@ -0,0 +1,330 @@
> +// 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 <drm/drm_atomic_helper.h>
> +#include <drm/drm_bridge.h>
> +#include <drm/drm_of.h>
> +#include <drm/drm_panel.h>
> +#include <drm/drm_print.h>
drm_print.h is no longer used and should be dropped.

> +#include <drm/drm_probe_helper.h>
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +
> +#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),
> +};
> +
> +/* DCON_REG_BRIGHT */
> +enum {
> +	BRIGHT_MASK		= GENMASK(7, 0),
> +};
> +
> +struct hx8837_priv {
> +	struct device *dev;
> +	struct regmap *regmap;
> +	struct gpio_desc *load_gpio;
> +
> +	struct drm_bridge *panel_bridge;
> +	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)
> +		dev_err(priv->dev, "error enabling the dcon load: %d\n", ret);
I assume this is disabling the dcon load - so text needs an update

> +
> +	ret = regmap_update_bits(priv->regmap, DCON_REG_MODE,
> +					       MODE_PASSTHRU |
> +					       MODE_SLEEP,
> +					       MODE_PASSTHRU |
> +					       MODE_SLEEP);
> +	if (ret)
> +		dev_err(priv->dev, "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)
> +		dev_err(priv->dev, "error enabling the dcon: %d\n", ret);
> +
> +	ret = gpiod_direction_output(priv->load_gpio, 1);
> +	if (ret)
> +		dev_err(priv->dev, "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,
> +					       BRIGHT_MASK,
> +					       backlight_get_brightness(bl));
> +	if (ret) {
> +		dev_err(&bl->dev, "error setting the backlight: %d\n", ret);
> +		return ret;
> +	}
> +
> +	if (backlight_get_brightness(bl))
> +		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 = BRIGHT_MASK,
> +	};
I have recently learned we shall also always set the scale.
This is missing in many drivers - but please do it here.

> +	struct device *dev = &client->dev;
> +	struct backlight_device *bl;
> +	struct hx8837_priv *priv;
> +	struct drm_panel *panel;
> +	unsigned int val;
> +	int ret;
> +
> +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	dev_set_drvdata(dev, priv);
> +	priv->dev = dev;
> +
> +	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, &panel, NULL);
> +	if (ret)
> +		return ret;
> +
> +	if (panel->backlight) {
> +		dev_err(dev, "the panel already has a backlight controller\n");
> +		return -ENODEV;
> +	}
> +
> +	priv->panel_bridge = devm_drm_panel_bridge_add(dev, 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");
regmap_init_i2c failed?

> +		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);
> +	}
> +
> +	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");
Debug - not needed
> +	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);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id hx8837_dt_ids[] = {
> +	{ .compatible = "himax,hx8837", },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, hx8837_dt_ids);
> +
> +static const struct i2c_device_id hx8837_ids[] = {
> +	{ "hx8837", 0 },
> +	{ /* sentinel */ }
> +};
> +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@...sk>");
> +MODULE_DESCRIPTION("HiMax HX8837 Display Controller Driver");
> +MODULE_LICENSE("GPL");
> -- 
> 2.28.0

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