Date:   Tue, 20 Mar 2018 15:00:06 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>
Cc:     architt@...eaurora.org, a.hajda@...sung.com, airlied@...ux.ie,
        horms@...ge.net.au, magnus.damm@...il.com, geert@...ux-m68k.org,
        niklas.soderlund@...natech.se, sergei.shtylyov@...entembedded.com,
        robh+dt@...nel.org, mark.rutland@....com,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/3] drm: bridge: Add thc63lvd1024 LVDS decoder driver

Hi Jacopo,

Thank you for the patch.

On Friday, 16 March 2018 17:16:38 EET Jacopo Mondi wrote:
> Add DRM bridge driver for Thine THC63LVD1024 LVDS to digital parallel
> output converter.
> 
> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
> Reviewed-by: Andrzej Hajda <a.hajda@...sung.com>
> Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
> ---
>  drivers/gpu/drm/bridge/Kconfig        |   6 +
>  drivers/gpu/drm/bridge/Makefile       |   1 +
>  drivers/gpu/drm/bridge/thc63lvd1024.c | 255 +++++++++++++++++++++++++++++++
>  3 files changed, 262 insertions(+)
>  create mode 100644 drivers/gpu/drm/bridge/thc63lvd1024.c

I'm aware that you started with a generic driver and then moved to a chip-
specific driver and that it caused issues. I however believe it was a good 
design, but we can make the driver generic later when a second similar chip 
will need to be supported.

> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> index 3b99d5a..5815a20 100644
> --- a/drivers/gpu/drm/bridge/Kconfig
> +++ b/drivers/gpu/drm/bridge/Kconfig
> @@ -92,6 +92,12 @@ config DRM_SII9234
>  	  It is an I2C driver, that detects connection of MHL bridge
>  	  and starts encapsulation of HDMI signal.
> 
> +config DRM_THINE_THC63LVD1024
> +	tristate "Thine THC63LVD1024 LVDS decoder bridge"
> +	depends on OF
> +	---help---
> +	  Thine THC63LVD1024 LVDS/parallel converter driver.
> +
>  config DRM_TOSHIBA_TC358767
>  	tristate "Toshiba TC358767 eDP bridge"
>  	depends on OF
> diff --git a/drivers/gpu/drm/bridge/Makefile
> b/drivers/gpu/drm/bridge/Makefile index 373eb28..fd90b16 100644
> --- a/drivers/gpu/drm/bridge/Makefile
> +++ b/drivers/gpu/drm/bridge/Makefile
> @@ -8,6 +8,7 @@ obj-$(CONFIG_DRM_PARADE_PS8622) += parade-ps8622.o
>  obj-$(CONFIG_DRM_SIL_SII8620) += sil-sii8620.o
>  obj-$(CONFIG_DRM_SII902X) += sii902x.o
>  obj-$(CONFIG_DRM_SII9234) += sii9234.o
> +obj-$(CONFIG_DRM_THINE_THC63LVD1024) += thc63lvd1024.o
>  obj-$(CONFIG_DRM_TOSHIBA_TC358767) += tc358767.o
>  obj-$(CONFIG_DRM_ANALOGIX_DP) += analogix/
>  obj-$(CONFIG_DRM_I2C_ADV7511) += adv7511/
> diff --git a/drivers/gpu/drm/bridge/thc63lvd1024.c
> b/drivers/gpu/drm/bridge/thc63lvd1024.c new file mode 100644
> index 0000000..02a54c2
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/thc63lvd1024.c
> @@ -0,0 +1,255 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * THC63LVD1024 LVDS to parallel data DRM bridge driver.
> + *
> + * Copyright (C) 2018 Jacopo Mondi <jacopo+renesas@...ndi.org>
> + */
> +
> +#include <drm/drmP.h>
> +#include <drm/drm_bridge.h>
> +#include <drm/drm_panel.h>
> +
> +#include <linux/gpio/consumer.h>
> +#include <linux/of_graph.h>
> +#include <linux/regulator/consumer.h>
> +
> +enum {

Please name the enumeration.

> +	THC63_LVDS_IN0,
> +	THC63_LVDS_IN1,
> +	THC63_DIGITAL_OUT0,
> +	THC63_DIGITAL_OUT1,

Strictly speaking LVDS is digital too. Maybe THC63_RGB_OUT* ?

> +};
> +
> +static const char * const thc63_reg_names[] = {
> +	"vcc", "lvcc", "pvcc", "cvcc",
> +};
> +
> +struct thc63_dev {
> +	struct device *dev;
> +
> +	struct regulator *vccs[ARRAY_SIZE(thc63_reg_names)];
> +
> +	struct gpio_desc *pdwn;
> +	struct gpio_desc *oe;
> +
> +	struct drm_bridge bridge;
> +	struct drm_bridge *next;
> +};
> +
> +static inline struct thc63_dev *to_thc63(struct drm_bridge *bridge)
> +{
> +	return container_of(bridge, struct thc63_dev, bridge);
> +}
> +
> +static int thc63_attach(struct drm_bridge *bridge)
> +{
> +	struct thc63_dev *thc63 = to_thc63(bridge);
> +
> +	return drm_bridge_attach(bridge->encoder, thc63->next, bridge);
> +}
> +
> +static void thc63_enable(struct drm_bridge *bridge)
> +{
> +	struct thc63_dev *thc63 = to_thc63(bridge);
> +	struct regulator *vcc;
> +	int i;
> + 
> +	for (i = 0; i < ARRAY_SIZE(thc63->vccs); i++) {
> +		vcc = thc63->vccs[i];
> +		if (!vcc)
> +			continue;
> +
> +		if (regulator_enable(vcc))

You can operate on thc63->vccs[i] directly without a local variable, here and 
below in the functions that handle regulators.

> +			goto error_vcc_enable;
> +	}

I thought about proposing usage of the regulators bulk API but it doesn't 
support optional regulators :-( If you agree with my proposal to make all 
regulators mandatory, please consider the bulk API to simplify power supply 
handling. If on the other hand you agree with my proposal to keep the vcc 
supply only, it won't matter.

> +	if (thc63->pdwn)
> +		gpiod_set_value(thc63->pdwn, 0);
> +
> +	if (thc63->oe)
> +		gpiod_set_value(thc63->oe, 1);
> +
> +	return;
> +
> +error_vcc_enable:
> +	dev_err(thc63->dev, "Failed to enable regulator %s\n",
> +		thc63_reg_names[i]);

I'd move the error message right before the goto.

> +	for (i = i - 1; i >= 0; i--) {
> +		vcc = thc63->vccs[i];
> +		if (!vcc)
> +			continue;
> +
> +		regulator_disable(vcc);
> +	}
> +}
> +
> +static void thc63_disable(struct drm_bridge *bridge)
> +{
> +	struct thc63_dev *thc63 = to_thc63(bridge);
> +	struct regulator *vcc;
> +	int i;
> +
> +	if (thc63->oe)
> +		gpiod_set_value(thc63->oe, 0);
> +
> +	if (thc63->pdwn)
> +		gpiod_set_value(thc63->pdwn, 1);
> +
> +	for (i = ARRAY_SIZE(thc63->vccs) - 1; i >= 0; i--) {
> +		vcc = thc63->vccs[i];
> +		if (!vcc)
> +			continue;
> +
> +		if (regulator_disable(vcc))
> +			dev_dbg(thc63->dev,
> +				"Failed to disable regulator %s\n",
> +				thc63_reg_names[i]);
> +	}
> +}
> +
> +struct drm_bridge_funcs thc63_bridge_func = {

static const

> +	.attach	= thc63_attach,
> +	.enable = thc63_enable,
> +	.disable = thc63_disable,
> +};
> +
> +static int thc63_parse_dt(struct thc63_dev *thc63)
> +{
> +	struct device_node *thc63_out;
> +	struct device_node *remote;
> +	int ret = 0;
> +
> +	thc63_out = of_graph_get_endpoint_by_regs(thc63->dev->of_node,
> +						  THC63_DIGITAL_OUT0, -1);
> +	if (!thc63_out) {
> +		dev_err(thc63->dev, "Missing endpoint in Port@%u\n",
> +			THC63_DIGITAL_OUT0);
> +		return -ENODEV;
> +	}
> +
> +	remote = of_graph_get_remote_port_parent(thc63_out);

	of_node_put(thc63_out);

here, it will simplify error handling.

> +	if (!remote) {
> +		dev_err(thc63->dev, "Endpoint in Port@%u unconnected\n",
> +			THC63_DIGITAL_OUT0);
> +		ret = -ENODEV;
> +		goto error_put_out_node;
> +	}
> +
> +	if (!of_device_is_available(remote)) {
> +		dev_err(thc63->dev, "Port@%u remote endpoint is disabled\n",
> +			THC63_DIGITAL_OUT0);
> +		ret = -ENODEV;
> +		goto error_put_remote_node;
> +	}
> +
> +	thc63->next = of_drm_find_bridge(remote);
> +	if (!thc63->next)
> +		ret = -EPROBE_DEFER;

You can add a return 0 here (and a goto in the previous check. Going through 
error labels in the non-error case is confusing. As a result you can avoid 
initializing ret to 0.

> +error_put_remote_node:
> +	of_node_put(remote);
> +error_put_out_node:
> +	of_node_put(thc63_out);
> +
> +	return ret;
> +}
> +
> +static int thc63_gpio_init(struct thc63_dev *thc63)
> +{
> +	thc63->oe = devm_gpiod_get_optional(thc63->dev, "oe", GPIOD_OUT_LOW);
> +	if (IS_ERR(thc63->oe)) {
> +		dev_err(thc63->dev, "Unable to get \"oe-gpios\"\n");

You can add the error code to the message, it could be helpful.

> +		return PTR_ERR(thc63->oe);
> +	}
> +
> +	thc63->pdwn = devm_gpiod_get_optional(thc63->dev, "pdwn",
> +					      GPIOD_OUT_HIGH);
> +	if (IS_ERR(thc63->pdwn)) {
> +		dev_err(thc63->dev, "Unable to get \"pdwn-gpios\"\n");

Same here.

> +		return PTR_ERR(thc63->pdwn);
> +	}
> +
> +	return 0;
> +}
> +
> +static int thc63_regulator_init(struct thc63_dev *thc63)
> +{
> +	struct regulator **reg;
> +	int i;

i is never negative, you can make it an unsigned int.

> +	reg = &thc63->vccs[0];
> +	for (i = 0; i < ARRAY_SIZE(thc63->vccs); i++, reg++) {
> +		*reg = devm_regulator_get_optional(thc63->dev,
> +						   thc63_reg_names[i]);
> +		if (IS_ERR(*reg)) {
> +			if (PTR_ERR(*reg) == -EPROBE_DEFER)
> +				return -EPROBE_DEFER;
> +			*reg = NULL;
> +		}
> +	}

Wouldn't the following be simpler ?

	for (i = 0; i < ARRAY_SIZE(thc63->vccs); i++) {
		struct regulator *reg;

		reg = devm_regulator_get_optional(thc63->dev,
						   thc63_reg_names[i]);
		if (IS_ERR(reg)) {
			if (PTR_ERR(reg) == -EPROBE_DEFER)
				return -EPROBE_DEFER;
			reg = NULL;
		}

		thc63->vccs[i] = reg;
	}

> +	return 0;
> +}
> +
> +static int thc63_probe(struct platform_device *pdev)
> +{
> +	struct thc63_dev *thc63;
> +	int ret;
> +
> +	thc63 = devm_kzalloc(&pdev->dev, sizeof(*thc63), GFP_KERNEL);
> +	if (!thc63)
> +		return -ENOMEM;
> +
> +	thc63->dev = &pdev->dev;
> +	platform_set_drvdata(pdev, thc63);
> +
> +	ret = thc63_regulator_init(thc63);
> +	if (ret)
> +		return ret;
> +
> +	ret = thc63_gpio_init(thc63);
> +	if (ret)
> +		return ret;
> +
> +	ret = thc63_parse_dt(thc63);
> +	if (ret)
> +		return ret;
> +
> +	thc63->bridge.driver_private = thc63;
> +	thc63->bridge.of_node = pdev->dev.of_node;
> +	thc63->bridge.funcs = &thc63_bridge_func;
> +
> +	drm_bridge_add(&thc63->bridge);
> +
> +	return 0;
> +}
> +
> +static int thc63_remove(struct platform_device *pdev)
> +{
> +	struct thc63_dev *thc63 = platform_get_drvdata(pdev);
> +
> +	drm_bridge_remove(&thc63->bridge);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id thc63_match[] = {
> +	{ .compatible = "thine,thc63lvd1024", },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, thc63_match);
> +
> +static struct platform_driver thc63_driver = {
> +	.probe	= thc63_probe,
> +	.remove	= thc63_remove,
> +	.driver	= {
> +		.name		= "thc63lvd1024",
> +		.of_match_table	= thc63_match,
> +	},
> +};
> +module_platform_driver(thc63_driver);
> +
> +MODULE_AUTHOR("Jacopo Mondi <jacopo@...ndi.org>");
> +MODULE_DESCRIPTION("Thine THC63LVD1024 LVDS decoder DRM bridge driver");
> +MODULE_LICENSE("GPL v2");

-- 
Regards,

Laurent Pinchart

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