Date:	Fri, 5 Jun 2015 14:19:39 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Heiko Schocher <hs@...x.de>
Cc:	linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/panel: add lg4573 driver

On Wed, May 06, 2015 at 09:49:33AM +0200, Heiko Schocher wrote:
> The patch adds LG4573 parallel RGB panel driver with SPI control interface.
> The driver uses drm_panel framework.

This should be obvious by the location of the driver. Can you instead
provide information about the type or resolution of the panel?

>  .../devicetree/bindings/panel/lg,lg4573.txt        |  42 +++
>  drivers/gpu/drm/panel/Kconfig                      |   8 +
>  drivers/gpu/drm/panel/Makefile                     |   1 +
>  drivers/gpu/drm/panel/panel-lg4573.c               | 367 +++++++++++++++++++++
>  4 files changed, 418 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/panel/lg,lg4573.txt
>  create mode 100644 drivers/gpu/drm/panel/panel-lg4573.c
> 
> diff --git a/Documentation/devicetree/bindings/panel/lg,lg4573.txt b/Documentation/devicetree/bindings/panel/lg,lg4573.txt
> new file mode 100644
> index 0000000..55f495d
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/panel/lg,lg4573.txt
> @@ -0,0 +1,42 @@
> +LG LG4573 TFT liquid crystal display with SPI control bus

Please capitalize "Liquid Crystal Display".

> +
> +Required properties:
> +  - compatible: "lg4573"

This is missing the vendor prefix.

> +  - reg: address of the panel on SPI bus

"on the"

> +  - display-timings: timings for the connected panel according to [1]

The timings are already implied by the compatible value, so there's no
need to list them in DT.

> +The panel must obey rules for SPI slave device specified in document [2].
> +
> +Optional properties:
> +  - power-on-delay: delay after turning regulators on [ms]

How is this a board-specific property? I'd assume that the same panel
always requires the same delay. Perhaps if this is board-specific it
really should be in the corresponding regulator's
regulator-enable-ramp-delay? Then again the binding doesn't describe any
regulators, so what exactly is this delay used for?

> +
> +[1]: Documentation/devicetree/bindings/video/display-timing.txt
> +[2]: Documentation/devicetree/bindings/spi/spi-bus.txt
> +
> +Example:
> +
> +	lcd_panel: display@0 {
> +		#address-cells = <1>;
> +		#size-cells = <1>;
> +		compatible = "lg,lg4573";
> +		spi-max-frequency = <10000000>;
> +		reset-gpios = <&gpio2 11 0>;

This isn't documented above.

> +		reg = <0>;
> +		power-on-delay = <10>;
> +		display-timings {
> +			480x800p57 {
> +				native-mode;
> +				clock-frequency = <27000027>;
> +				hactive = <480>;
> +				vactive = <800>;
> +				hfront-porch = <10>;
> +				hback-porch = <59>;
> +				hsync-len = <10>;
> +				vback-porch = <15>;
> +				vfront-porch = <15>;
> +				vsync-len = <15>;
> +				hsync-active = <1>;
> +				vsync-active = <1>;
> +			};
> +		};
> +	};
> diff --git a/drivers/gpu/drm/panel/Kconfig b/drivers/gpu/drm/panel/Kconfig
> index 6d64c7b..29c3407 100644
> --- a/drivers/gpu/drm/panel/Kconfig
> +++ b/drivers/gpu/drm/panel/Kconfig
> @@ -23,6 +23,14 @@ config DRM_PANEL_LD9040
>  	depends on OF && SPI
>  	select VIDEOMODE_HELPERS
>  
> +config DRM_PANEL_LG4573
> +	tristate "LG4573 RGB/SPI panel"

I'd like to get into the habit of prefixing the panels with a vendor
prefix, so this should become something like:

	config DRM_PANEL_LG_LG4573
		tristate "LG LG4573 RGB/SPI panel"

I have a local patch that converts existing boards, so with this
conversion it'd fit right it.

> diff --git a/drivers/gpu/drm/panel/Makefile b/drivers/gpu/drm/panel/Makefile
> index 4b2a043..715b95d 100644
> --- a/drivers/gpu/drm/panel/Makefile
> +++ b/drivers/gpu/drm/panel/Makefile
> @@ -1,4 +1,5 @@
>  obj-$(CONFIG_DRM_PANEL_SIMPLE) += panel-simple.o
>  obj-$(CONFIG_DRM_PANEL_LD9040) += panel-ld9040.o
> +obj-$(CONFIG_DRM_PANEL_LG4573) += panel-lg4573.o

Similarly for filenames, this would become: panel-lg-lg4573.c

>  obj-$(CONFIG_DRM_PANEL_S6E8AA0) += panel-s6e8aa0.o
>  obj-$(CONFIG_DRM_PANEL_SHARP_LQ101R1SX01) += panel-sharp-lq101r1sx01.o
> diff --git a/drivers/gpu/drm/panel/panel-lg4573.c b/drivers/gpu/drm/panel/panel-lg4573.c
> new file mode 100644
> index 0000000..9d5e5a5
> --- /dev/null
> +++ b/drivers/gpu/drm/panel/panel-lg4573.c
> @@ -0,0 +1,367 @@
> +/*
> + *
> + * Copyright (C) 2015 Heiko Schocher <hs@...x.de>
> + *
> + * from:
> + * drivers/gpu/drm/panel/panel-ld9040.c
> + * ld9040 AMOLED LCD drm_panel driver.
> + *
> + * Copyright (c) 2014 Samsung Electronics Co., Ltd
> + * Derived from drivers/video/backlight/ld9040.c
> + *
> + * Andrzej Hajda <a.hajda@...sung.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> +*/
> +
> +#include <drm/drmP.h>
> +#include <drm/drm_panel.h>
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/regulator/consumer.h>
> +#include <linux/spi/spi.h>
> +
> +#include <video/mipi_display.h>
> +#include <video/of_videomode.h>
> +#include <video/videomode.h>
> +
> +struct lg4573 {
> +	struct device *dev;
> +	struct drm_panel panel;

Might be a slight optimization to put panel first in the structure.

> +	u32 power_on_delay;
> +	struct videomode vm;
> +};
> +
> +static inline struct lg4573 *panel_to_lg4573(struct drm_panel *panel)
> +{
> +	return container_of(panel, struct lg4573, panel);
> +}
> +
> +static int lg4573_spi_write_u16(struct lg4573 *ctx, u16 data)
> +{
> +	struct spi_device *spi = to_spi_device(ctx->dev);
> +	struct spi_transfer xfer = {
> +		.len		= 2,

No need for this padding. A single space will do.

> +	};
> +	struct spi_message msg;
> +	u16 temp = htons(data);

htons() always has this association to network programming. Perhaps it'd
be better to use cpu_to_be16() here?

> +
> +	dev_dbg(ctx->dev, "writing data: %x\n", data);
> +	xfer.tx_buf = &temp;
> +	spi_message_init(&msg);
> +	spi_message_add_tail(&xfer, &msg);
> +
> +	return spi_sync(spi, &msg);
> +}
> +
> +static void lg4573_spi_write_u16_array(struct lg4573 *ctx, u16 *buff, int size)

size should be of type size_t. Or in this case it's really a count, so
perhaps rename to count and make it unsigned int.

> +{
> +	int idx;

Then this would become unsigned int as well. And a more idiomatic name
would be i.

> +
> +	for (idx = 0; idx < size; idx++)
> +		lg4573_spi_write_u16(ctx, buff[idx]);
> +}

You completely ignore errors.

> +static void lg4573_display_on(struct lg4573 *ctx)
> +{
> +	static u16 sleep_out = 0x7011;
> +	static u16 display_on = 0x7029;

These seem to be (0x70 << 8 | MIPI_DCS_EXIT_SLEEP) and (0x70 << 8 |
MIPI_DCS_SET_DISPLAY_ON). Perhaps that 0x70 just means it's followed by
a MIPI DCS command, so I'm thinking perhaps you should add a function
such as lg4573_spi_write_dcs() which only takes the DCS command to avoid
all the repetition.

> +
> +	lg4573_spi_write_u16(ctx, sleep_out);
> +	msleep(ctx->power_on_delay);
> +	lg4573_spi_write_u16(ctx, display_on);
> +}

This also ignores errors. And the post-regulator delay is used here but
I don't see any regulators being powered up. According to the MIPI DCS
specification there needs to be a delay of 5 ms after the EXIT_SLEEP
command and any other command (120 ms if the command is ENTER_SLEEP).
Perhaps that's what you're after here? It would mean that the delay is
not board-specific and hence doesn't belong in DT.

> +static int lg4573_display_off(struct lg4573 *ctx)
> +{
> +	static u16 display_off = 0x7028;
> +	static u16 sleep_in	= 0x7010;

More standard DCS commands. Also unnecessary tab, it should be a single
space instead.

> +
> +	lg4573_spi_write_u16(ctx, display_off);
> +	msleep(ctx->power_on_delay);
> +	lg4573_spi_write_u16(ctx, sleep_in);
> +	return 0;
> +}

Also it's weird that this function returns a value. It always returns 0
so there's no point, really. You should perhaps think about propagating
any errors from the SPI write.

> +
> +static void lg4573_display_mode_settings(struct lg4573 *ctx)
> +{
> +	static u16 display_mode_settings[] = {
> +	  0x703A,
[...]
> +	  0x7200,
> +	};

Please make use of the 78/80 columns. Also, I don't suppose it'd be
possible to obtain symbolic names for these magic numbers? More of the
same below.

> +static void lg4573_init(struct lg4573 *ctx)
> +{
> +	dev_dbg(ctx->dev, "initializing LCD\n");
> +
> +	lg4573_display_mode_settings(ctx);
> +	lg4573_power_settings(ctx);
> +	lg4573_gamma_settings(ctx);
> +}
> +
> +static int lg4573_power_on(struct lg4573 *ctx)
> +{
> +	msleep(ctx->power_on_delay);
> +	lg4573_display_on(ctx);
> +	return 0;
> +}
> +
> +static int lg4573_disable(struct drm_panel *panel)
> +{
> +	struct lg4573 *ctx = panel_to_lg4573(panel);
> +
> +	return lg4573_display_off(ctx);
> +}
> +
> +static int lg4573_enable(struct drm_panel *panel)
> +{
> +	struct lg4573 *ctx = panel_to_lg4573(panel);
> +	int ret;
> +
> +	lg4573_init(ctx);
> +
> +	ret = lg4573_power_on(ctx);
> +
> +	return ret;
> +}

I think these should all propagate errors.

> +static int lg4573_get_modes(struct drm_panel *panel)
> +{
> +	struct drm_connector *connector = panel->connector;
> +	struct lg4573 *ctx = panel_to_lg4573(panel);
> +	struct drm_display_mode *mode;
> +
> +	mode = drm_mode_create(connector->dev);
> +	if (!mode) {
> +		DRM_ERROR("failed to create a new display mode\n");
> +		return 0;
> +	}
> +
> +	drm_display_mode_from_videomode(&ctx->vm, mode);
> +
> +	mode->type = DRM_MODE_TYPE_DRIVER | DRM_MODE_TYPE_PREFERRED;
> +	drm_mode_probed_add(connector, mode);
> +
> +	return 1;
> +}

You can either use a hard-coded mode or use display timings along with
the helpers to convert the timings to a default mode. No need to parse
the information from DT.

> +static const struct drm_panel_funcs lg4573_drm_funcs = {
> +	.disable = lg4573_disable,
> +	.enable = lg4573_enable,
> +	.get_modes = lg4573_get_modes,
> +};
> +
> +static int lg4573_parse_dt(struct lg4573 *ctx)
> +{
> +	struct device *dev = ctx->dev;
> +	struct device_node *np = dev->of_node;
> +	int ret;
> +
> +	ret = of_get_videomode(np, &ctx->vm, 0);
> +	if (ret < 0)
> +		return ret;
> +
> +	of_property_read_u32(np, "power-on-delay", &ctx->power_on_delay);
> +
> +	return 0;
> +}
> +
> +static int lg4573_probe(struct spi_device *spi)
> +{
> +	struct device *dev = &spi->dev;
> +	struct lg4573 *ctx;
> +	int ret;
> +
> +	ctx = devm_kzalloc(dev, sizeof(struct lg4573), GFP_KERNEL);
> +	if (!ctx)
> +		return -ENOMEM;
> +
> +	spi_set_drvdata(spi, ctx);
> +	ctx->dev = dev;
> +
> +	ret = lg4573_parse_dt(ctx);
> +	if (ret < 0)
> +		return ret;
> +
> +	spi->bits_per_word = 8;
> +	ret = spi_setup(spi);
> +	if (ret < 0) {
> +		dev_err(dev, "spi setup failed.\n");

You might want to include the error code in the message. Also "SPI".

> +static const struct of_device_id lg4573_of_match[] = {
> +	{ .compatible = "lg,lg4573" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, lg4573_of_match);
> +
> +static struct spi_driver lg4573_driver = {
> +	.probe		= lg4573_probe,
> +	.remove		= lg4573_remove,
> +	.driver = {
> +		.name	= "lg4573",
> +		.owner	= THIS_MODULE,
> +		.of_match_table = lg4573_of_match,
> +	},

No need for the padding. It's not consistent anyway.

Thierry

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