Re: [PATCH v2 2/2] drm/bridge: anx7688: Add anx7688 bridge driver support

[Andrzej Hajda <a.hajda@samsung.com>]

On 13.02.2020 15:54, Enric Balletbo i Serra wrote:
> From: Nicolas Boichat <drinkcat@chromium.org>
>
> ANX7688 is a HDMI to DP converter (as well as USB-C port controller),
> that has an internal microcontroller.
>
> The only reason a Linux kernel driver is necessary is to reject
> resolutions that require more bandwidth than what is available on
> the DP side. DP bandwidth and lane count are reported by the bridge
> via 2 registers on I2C.
>
> Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
> Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
> ---
>
> Changes in v2:
> - Move driver to drivers/gpu/drm/bridge/analogix.
> - Make the driver OF only so we can reduce the ifdefs.
> - Update the Copyright to 2020.
> - Use probe_new so we can get rid of the i2c_device_id table.
>
>  drivers/gpu/drm/bridge/analogix/Kconfig       |  12 ++
>  drivers/gpu/drm/bridge/analogix/Makefile      |   1 +
>  .../drm/bridge/analogix/analogix-anx7688.c    | 188 ++++++++++++++++++
>  3 files changed, 201 insertions(+)
>  create mode 100644 drivers/gpu/drm/bridge/analogix/analogix-anx7688.c
>
> diff --git a/drivers/gpu/drm/bridge/analogix/Kconfig b/drivers/gpu/drm/bridge/analogix/Kconfig
> index e1fa7d820373..af7c2939403c 100644
> --- a/drivers/gpu/drm/bridge/analogix/Kconfig
> +++ b/drivers/gpu/drm/bridge/analogix/Kconfig
> @@ -11,6 +11,18 @@ config DRM_ANALOGIX_ANX6345
>  	  ANX6345 transforms the LVTTL RGB output of an
>  	  application processor to eDP or DisplayPort.
>  
> +config DRM_ANALOGIX_ANX7688
> +	tristate "Analogix ANX7688 bridge"
> +	depends on OF
> +	select DRM_KMS_HELPER
> +	select REGMAP_I2C
> +	help
> +	  ANX7688 is an ultra-low power 4k Ultra-HD (4096x2160p60)
> +	  mobile HD transmitter designed for portable devices. The
> +	  ANX7688 converts HDMI 2.0 to DisplayPort 1.3 Ultra-HD
> +	  including an intelligent crosspoint switch to support
> +	  USB Type-C.
> +
>  config DRM_ANALOGIX_ANX78XX
>  	tristate "Analogix ANX78XX bridge"
>  	select DRM_ANALOGIX_DP
> diff --git a/drivers/gpu/drm/bridge/analogix/Makefile b/drivers/gpu/drm/bridge/analogix/Makefile
> index 97669b374098..27cd73635c8c 100644
> --- a/drivers/gpu/drm/bridge/analogix/Makefile
> +++ b/drivers/gpu/drm/bridge/analogix/Makefile
> @@ -1,5 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  analogix_dp-objs := analogix_dp_core.o analogix_dp_reg.o analogix-i2c-dptx.o
>  obj-$(CONFIG_DRM_ANALOGIX_ANX6345) += analogix-anx6345.o
> +obj-$(CONFIG_DRM_ANALOGIX_ANX7688) += analogix-anx7688.o
>  obj-$(CONFIG_DRM_ANALOGIX_ANX78XX) += analogix-anx78xx.o
>  obj-$(CONFIG_DRM_ANALOGIX_DP) += analogix_dp.o
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix-anx7688.c b/drivers/gpu/drm/bridge/analogix/analogix-anx7688.c
> new file mode 100644
> index 000000000000..10a7cd0f9126
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/analogix/analogix-anx7688.c
> @@ -0,0 +1,188 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * ANX7688 HDMI->DP bridge driver
> + *
> + * Copyright 2020 Google LLC
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +#include <linux/regmap.h>
> +#include <drm/drm_bridge.h>
> +
> +/* Register addresses */
> +#define VENDOR_ID_REG 0x00
> +#define DEVICE_ID_REG 0x02
> +
> +#define FW_VERSION_REG 0x80
> +
> +#define DP_BANDWIDTH_REG 0x85
> +#define DP_LANE_COUNT_REG 0x86
> +
> +#define VENDOR_ID 0x1f29
> +#define DEVICE_ID 0x7688
> +
> +/* First supported firmware version (0.85) */
> +#define MINIMUM_FW_VERSION 0x0085
> +
> +struct anx7688 {
> +	struct drm_bridge bridge;
> +	struct i2c_client *client;
> +	struct regmap *regmap;
> +
> +	bool filter;
> +};
> +
> +static inline struct anx7688 *bridge_to_anx7688(struct drm_bridge *bridge)
> +{
> +	return container_of(bridge, struct anx7688, bridge);
> +}
> +
> +static bool anx7688_bridge_mode_fixup(struct drm_bridge *bridge,
> +				      const struct drm_display_mode *mode,
> +				      struct drm_display_mode *adjusted_mode)
> +{
> +	struct anx7688 *anx7688 = bridge_to_anx7688(bridge);
> +	int totalbw, requiredbw;
> +	u8 dpbw, lanecount;
> +	u8 regs[2];
> +	int ret;
> +
> +	if (!anx7688->filter)
> +		return true;
> +
> +	/* Read both regs 0x85 (bandwidth) and 0x86 (lane count). */
> +	ret = regmap_bulk_read(anx7688->regmap, DP_BANDWIDTH_REG, regs, 2);
> +	if (ret < 0) {
> +		dev_err(&anx7688->client->dev,
> +			"Failed to read bandwidth/lane count\n");
> +		return false;
> +	}
> +	dpbw = regs[0];
> +	lanecount = regs[1];


Are these values hw invariant? Or they are result of cable probe/training?

In 1st case this code should go rather to mode_valid.


> +
> +	/* Maximum 0x19 bandwidth (6.75 Gbps Turbo mode), 2 lanes */
> +	if (dpbw > 0x19 || lanecount > 2) {
> +		dev_err(&anx7688->client->dev,
> +			"Invalid bandwidth/lane count (%02x/%d)\n",
> +			dpbw, lanecount);
> +		return false;
> +	}
> +
> +	/* Compute available bandwidth (kHz) */
> +	totalbw = dpbw * lanecount * 270000 * 8 / 10;
> +
> +	/* Required bandwidth (8 bpc, kHz) */
> +	requiredbw = mode->clock * 8 * 3;
> +
> +	dev_dbg(&anx7688->client->dev,
> +		"DP bandwidth: %d kHz (%02x/%d); mode requires %d Khz\n",
> +		totalbw, dpbw, lanecount, requiredbw);
> +
> +	if (totalbw == 0) {
> +		dev_warn(&anx7688->client->dev,
> +			 "Bandwidth/lane count are 0, not rejecting modes\n");
> +		return true;
> +	}
> +
> +	return totalbw >= requiredbw;
> +}
> +
> +static const struct drm_bridge_funcs anx7688_bridge_funcs = {
> +	.mode_fixup = anx7688_bridge_mode_fixup,
> +};
> +
> +static const struct regmap_config anx7688_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +};
> +
> +static int anx7688_i2c_probe(struct i2c_client *client)
> +{
> +	struct device *dev = &client->dev;
> +	struct anx7688 *anx7688;
> +	u16 vendor, device;
> +	u16 fwversion;
> +	u8 buffer[4];
> +	int ret;
> +
> +	anx7688 = devm_kzalloc(dev, sizeof(*anx7688), GFP_KERNEL);
> +	if (!anx7688)
> +		return -ENOMEM;
> +
> +	anx7688->bridge.of_node = dev->of_node;
> +	anx7688->client = client;
> +	i2c_set_clientdata(client, anx7688);
> +
> +	anx7688->regmap = devm_regmap_init_i2c(client, &anx7688_regmap_config);
> +
> +	/* Read both vendor and device id (4 bytes). */
> +	ret = regmap_bulk_read(anx7688->regmap, VENDOR_ID_REG, buffer, 4);
> +	if (ret) {
> +		dev_err(dev, "Failed to read chip vendor/device id\n");
> +		return ret;
> +	}
> +
> +	vendor = (u16)buffer[1] << 8 | buffer[0];
> +	device = (u16)buffer[3] << 8 | buffer[2];


Here we have little endian, and...


> +	if (vendor != VENDOR_ID || device != DEVICE_ID) {
> +		dev_err(dev, "Invalid vendor/device id %04x/%04x\n",
> +			vendor, device);
> +		return -ENODEV;
> +	}
> +
> +	ret = regmap_bulk_read(anx7688->regmap, FW_VERSION_REG, buffer, 2);
> +	if (ret) {
> +		dev_err(&client->dev, "Failed to read firmware version\n");
> +		return ret;
> +	}
> +
> +	fwversion = (u16)buffer[0] << 8 | buffer[1];


...here big endian.

Is it correct?


Overall driver looks OK.

Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>

 --
Regards
Andrzej


> +	dev_info(dev, "ANX7688 firwmare version %02x.%02x\n",
> +		 buffer[0], buffer[1]);
> +
> +	/* FW version >= 0.85 supports bandwidth/lane count registers */
> +	if (fwversion >= MINIMUM_FW_VERSION) {
> +		anx7688->filter = true;
> +	} else {
> +		/* Warn, but not fail, for backwards compatibility. */
> +		dev_warn(dev,
> +			 "Old ANX7688 FW version (%02x.%02x), not filtering\n",
> +			 buffer[0], buffer[1]);
> +	}
> +
> +	anx7688->bridge.funcs = &anx7688_bridge_funcs;
> +	drm_bridge_add(&anx7688->bridge);
> +
> +	return 0;
> +}
> +
> +static int anx7688_i2c_remove(struct i2c_client *client)
> +{
> +	struct anx7688 *anx7688 = i2c_get_clientdata(client);
> +
> +	drm_bridge_remove(&anx7688->bridge);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id anx7688_match_table[] = {
> +	{ .compatible = "analogix,anx7688", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, anx7688_match_table);
> +
> +static struct i2c_driver anx7688_driver = {
> +	.probe_new = anx7688_i2c_probe,
> +	.remove = anx7688_i2c_remove,
> +	.driver = {
> +		.name = "anx7688",
> +		.of_match_table = anx7688_match_table,
> +	},
> +};
> +
> +module_i2c_driver(anx7688_driver);
> +
> +MODULE_DESCRIPTION("ANX7688 HDMI->DP bridge driver");
> +MODULE_AUTHOR("Nicolas Boichat <drinkcat@chromium.org>");
> +MODULE_LICENSE("GPL");