RE: [PATCH v3 2/7] drm/bridge: Repurpose lvds-encoder.c

[Fabrizio Castro <fabrizio.castro@bp.renesas.com>]

Hello Laurent,

Thank you for your feedback!

> From: devicetree-owner@vger.kernel.org <devicetree-owner@vger.kernel.org> On Behalf Of Laurent Pinchart
> Sent: 07 November 2019 20:35
> Subject: Re: [PATCH v3 2/7] drm/bridge: Repurpose lvds-encoder.c
> 
> Hi Fabrizio,
> 
> Thank you for the patch.
> 
> On Thu, Nov 07, 2019 at 08:10:58PM +0000, Fabrizio Castro wrote:
> > lvds-encoder.c implementation is also suitable for LVDS decoders,
> > not just LVDS encoders.
> > Instead of creating a new driver for addressing support for
> > transparent LVDS decoders, repurpose lvds-encoder.c for the greater
> > good.
> >
> > Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
> >
> > ---
> > v2->v3:
> > * No change
> > v1->v2:
> > * No change
> > ---
> >  drivers/gpu/drm/bridge/Kconfig        |   8 +-
> >  drivers/gpu/drm/bridge/Makefile       |   2 +-
> >  drivers/gpu/drm/bridge/lvds-codec.c   | 131 ++++++++++++++++++++++++++++
> >  drivers/gpu/drm/bridge/lvds-encoder.c | 155 ----------------------------------
> >  4 files changed, 136 insertions(+), 160 deletions(-)
> 
> It would help if you added the -M1 option to git-format-patch to detect
> the rename, the result would be easier to review.

Will do, thank you for the hint

> 
> >  create mode 100644 drivers/gpu/drm/bridge/lvds-codec.c
> >  delete mode 100644 drivers/gpu/drm/bridge/lvds-encoder.c
> >
> > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> > index 3436297..9e75ca4e 100644
> > --- a/drivers/gpu/drm/bridge/Kconfig
> > +++ b/drivers/gpu/drm/bridge/Kconfig
> > @@ -45,14 +45,14 @@ config DRM_DUMB_VGA_DAC
> >  	  Support for non-programmable RGB to VGA DAC bridges, such as ADI
> >  	  ADV7123, TI THS8134 and THS8135 or passive resistor ladder DACs.
> >
> > -config DRM_LVDS_ENCODER
> > -	tristate "Transparent parallel to LVDS encoder support"
> > +config DRM_LVDS_CODEC
> > +	tristate "Transparent LVDS encoders and decoders support"
> >  	depends on OF
> >  	select DRM_KMS_HELPER
> >  	select DRM_PANEL_BRIDGE
> >  	help
> > -	  Support for transparent parallel to LVDS encoders that don't require
> > -	  any configuration.
> > +	  Support for transparent LVDS encoders and LVDS decoders that don't
> > +	  require any configuration.
> >
> >  config DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW
> >  	tristate "MegaChips stdp4028-ge-b850v3-fw and stdp2690-ge-b850v3-fw"
> > diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
> > index 4934fcf..8a9178a 100644
> > --- a/drivers/gpu/drm/bridge/Makefile
> > +++ b/drivers/gpu/drm/bridge/Makefile
> > @@ -2,7 +2,7 @@
> >  obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
> >  obj-$(CONFIG_DRM_CDNS_DSI) += cdns-dsi.o
> >  obj-$(CONFIG_DRM_DUMB_VGA_DAC) += dumb-vga-dac.o
> > -obj-$(CONFIG_DRM_LVDS_ENCODER) += lvds-encoder.o
> > +obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o
> >  obj-$(CONFIG_DRM_MEGACHIPS_STDPXXXX_GE_B850V3_FW) += megachips-stdpxxxx-ge-b850v3-fw.o
> >  obj-$(CONFIG_DRM_NXP_PTN3460) += nxp-ptn3460.o
> >  obj-$(CONFIG_DRM_PARADE_PS8622) += parade-ps8622.o
> > diff --git a/drivers/gpu/drm/bridge/lvds-codec.c b/drivers/gpu/drm/bridge/lvds-codec.c
> > new file mode 100644
> > index 0000000..d57a8eb
> > --- /dev/null
> > +++ b/drivers/gpu/drm/bridge/lvds-codec.c
> > @@ -0,0 +1,131 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Copyright (C) 2019 Renesas Electronics Corporation
> > + * Copyright (C) 2016 Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > + */
> > +
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/of_device.h>
> > +#include <linux/of_graph.h>
> > +#include <linux/platform_device.h>
> > +
> > +#include <drm/drm_bridge.h>
> > +#include <drm/drm_panel.h>
> > +
> > +struct lvds_codec {
> > +	struct drm_bridge bridge;
> > +	struct drm_bridge *panel_bridge;
> > +	struct gpio_desc *powerdown_gpio;
> > +};
> > +
> > +static int lvds_codec_attach(struct drm_bridge *bridge)
> > +{
> > +	struct lvds_codec *lvds_codec = container_of(bridge,
> > +						     struct lvds_codec, bridge);
> > +
> > +	return drm_bridge_attach(bridge->encoder, lvds_codec->panel_bridge,
> > +				 bridge);
> > +}
> > +
> > +static void lvds_codec_enable(struct drm_bridge *bridge)
> > +{
> > +	struct lvds_codec *lvds_codec = container_of(bridge,
> > +						     struct lvds_codec, bridge);
> > +
> > +	if (lvds_codec->powerdown_gpio)
> > +		gpiod_set_value_cansleep(lvds_codec->powerdown_gpio, 0);
> > +}
> > +
> > +static void lvds_codec_disable(struct drm_bridge *bridge)
> > +{
> > +	struct lvds_codec *lvds_codec = container_of(bridge,
> > +						     struct lvds_codec, bridge);
> > +
> > +	if (lvds_codec->powerdown_gpio)
> > +		gpiod_set_value_cansleep(lvds_codec->powerdown_gpio, 1);
> > +}
> > +
> > +static struct drm_bridge_funcs funcs = {
> > +	.attach = lvds_codec_attach,
> > +	.enable = lvds_codec_enable,
> > +	.disable = lvds_codec_disable,
> > +};
> > +
> > +static int lvds_codec_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct device_node *panel_node;
> > +	struct drm_panel *panel;
> > +	struct lvds_codec *lvds_codec;
> > +
> > +	lvds_codec = devm_kzalloc(dev, sizeof(*lvds_codec), GFP_KERNEL);
> > +	if (!lvds_codec)
> > +		return -ENOMEM;
> > +
> > +	lvds_codec->powerdown_gpio = devm_gpiod_get_optional(dev, "powerdown",
> > +							     GPIOD_OUT_HIGH);
> > +	if (IS_ERR(lvds_codec->powerdown_gpio))
> > +		return PTR_ERR(lvds_codec->powerdown_gpio);
> 
> The driver had an error message here, any reason it got removed ?

I am quoting from https://www.spinics.net/lists/devicetree/msg318602.html :
"I know it was there already, but this seems a bit unusual for the
minimal gain of having a printout in the very unlikely case the
gpiod_get() operations fails. I would just return PTR_ERR()."

I am OK with reinstating it, just let me know what you want me to do here.

> 
> > +
> > +	panel_node = of_graph_get_remote_node(dev->of_node, 1, 0);
> > +	if (!panel_node) {
> > +		dev_dbg(dev, "panel DT node not found\n");
> > +		return -ENXIO;
> > +	}
> > +
> > +	panel = of_drm_find_panel(panel_node);
> > +	of_node_put(panel_node);
> > +	if (IS_ERR(panel)) {
> > +		dev_dbg(dev, "panel not found, deferring probe\n");
> > +		return PTR_ERR(panel);
> > +	}
> > +
> > +	lvds_codec->panel_bridge = devm_drm_panel_bridge_add(dev, panel);
> 
> This was devm_drm_panel_bridge_add_typed(), do you think there's a risk
> of breaking userspace ? Of course as noted in the documentation of
> devm_drm_panel_bridge_add_typed() the right solution is to fix panel
> drivers, but I'm still slightly worried.

Things break when the panel doesn't define connector_type, leading to the below
check from devm_drm_panel_bridge_add:
if (WARN_ON(panel->connector_type == DRM_MODE_CONNECTOR_Unknown))        
    return NULL;

Please advise on the best course of action here.

> 
> Actually, could you split this patch in two, with a patch that only
> renames the driver (and the symbols internally) without any functional
> change, and another patch that performs the modifications ? That would
> be much easier to review and discuss.

Will do

> 
> > +	if (IS_ERR(lvds_codec->panel_bridge))
> > +		return PTR_ERR(lvds_codec->panel_bridge);
> > +
> > +	/* The panel_bridge bridge is attached to the panel's of_node,
> > +	 * but we need a bridge attached to our of_node for our user
> > +	 * to look up.
> > +	 */
> > +	lvds_codec->bridge.of_node = dev->of_node;
> > +	lvds_codec->bridge.funcs = &funcs;
> > +	drm_bridge_add(&lvds_codec->bridge);
> > +
> > +	platform_set_drvdata(pdev, lvds_codec);
> > +
> > +	return 0;
> > +}
> > +
> > +static int lvds_codec_remove(struct platform_device *pdev)
> > +{
> > +	struct lvds_codec *lvds_codec = platform_get_drvdata(pdev);
> > +
> > +	drm_bridge_remove(&lvds_codec->bridge);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id lvds_codec_match[] = {
> > +	{ .compatible = "lvds-encoder"  },
> > +	{ .compatible = "thine,thc63lvdm83d" },
> > +	{ .compatible = "lvds-decoder" },
> > +	{},
> > +};
> > +MODULE_DEVICE_TABLE(of, lvds_codec_match);
> > +
> > +static struct platform_driver lvds_codec_driver = {
> > +	.probe	= lvds_codec_probe,
> > +	.remove	= lvds_codec_remove,
> > +	.driver		= {
> > +		.name		= "lvds-codec",
> > +		.of_match_table	= lvds_codec_match,
> > +	},
> > +};
> > +module_platform_driver(lvds_codec_driver);
> > +
> > +MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
> > +MODULE_DESCRIPTION("Driver for transparent LVDS encoders and LVDS decoders");
> 
> Maybe "LVDS encoders and decoders" ?
> 
> > +MODULE_LICENSE("GPL");
> 
> [snip]
> 
> --
> Regards,
> 
> Laurent Pinchart