Hi Sam,

Le lun. 27 juil. 2020 à 22:31, Sam Ravnborg [off-list ref] a 
écrit :

Hi Paul.

On Mon, Jul 27, 2020 at 06:46:10PM +0200, Paul Cercueil wrote:

quoted

 This driver will register a DBI host driver for panels connected 
over
 SPI.

So this is actually a MIPI DBI host driver.

I personally would love to have added mipi_ in the names - to make it
all more explicit.
But maybe that just because I get confused on all the acronyms.

I can rename the driver and move it out of drm/bridge/, no problem.

Some details in the following. Will try to find some more time so I 
can
grasp the full picture. The following was just my low-level notes for
now.

	Sam

quoted

 DBI types c1 and c3 are supported. C1 is a SPI protocol with 9 bits 
per
 word, with the data/command information in the 9th (MSB) bit. C3 is 
a
 SPI protocol with 8 bits per word, with the data/command information
 carried by a separate GPIO.

We did not have any define to distingush between DBI_C1 and DBI_c3:
+/* MIPI bus types */
+#define MIPI_DEVICE_TYPE_DSI           BIT(0)
+#define MIPI_DEVICE_TYPE_DBI_SPI_MODE1 BIT(1)
+#define MIPI_DEVICE_TYPE_DBI_SPI_MODE2 BIT(2)
+#define MIPI_DEVICE_TYPE_DBI_SPI_MODE3 BIT(3)
+#define MIPI_DEVICE_TYPE_DBI_M6800     BIT(4)
+#define MIPI_DEVICE_TYPE_DBI_I8080     BIT(5)

Is this on purpose?

I understand the confusion. Here SPI_MODE1/3 actually mean SPI_C1/3. I 
will rename them.

I had assumed the host should tell what it supports and the device 
should
tell what it wanted.
So if the host did not support DBI_C3 and device wants it - then we
could give up early.

Well that's exactly what's done here - just with badly named macros :)

quoted

 Signed-off-by: Paul Cercueil [off-list ref]
 ---
  drivers/gpu/drm/bridge/Kconfig   |   8 +
  drivers/gpu/drm/bridge/Makefile  |   1 +
  drivers/gpu/drm/bridge/dbi-spi.c | 261 
+++++++++++++++++++++++++++++++

This is no bridge driver - so does not belong in the bridge
directory.
gpu/drm/drm_mipi_dbi_spi.c?

quoted

  3 files changed, 270 insertions(+)
  create mode 100644 drivers/gpu/drm/bridge/dbi-spi.c

 diff --git a/drivers/gpu/drm/bridge/Kconfig 
b/drivers/gpu/drm/bridge/Kconfig
 index c7f0dacfb57a..ed38366847c1 100644
 --- a/drivers/gpu/drm/bridge/Kconfig
 +++ b/drivers/gpu/drm/bridge/Kconfig
 @@ -219,6 +219,14 @@ config DRM_TI_TPD12S015
  	  Texas Instruments TPD12S015 HDMI level shifter and ESD 
protection
  	  driver.

 +config DRM_MIPI_DBI_SPI
 +	tristate "SPI host support for MIPI DBI"
 +	depends on OF && SPI
 +	select DRM_MIPI_DSI
 +	select DRM_MIPI_DBI
 +	help
 +	  Driver to support DBI over SPI.
 +
  source "drivers/gpu/drm/bridge/analogix/Kconfig"

  source "drivers/gpu/drm/bridge/adv7511/Kconfig"
 diff --git a/drivers/gpu/drm/bridge/Makefile 
b/drivers/gpu/drm/bridge/Makefile
 index 7d7c123a95e4..c2c522c2774f 100644
 --- a/drivers/gpu/drm/bridge/Makefile
 +++ b/drivers/gpu/drm/bridge/Makefile
 @@ -20,6 +20,7 @@ obj-$(CONFIG_DRM_I2C_ADV7511) += adv7511/
  obj-$(CONFIG_DRM_TI_SN65DSI86) += ti-sn65dsi86.o
  obj-$(CONFIG_DRM_TI_TFP410) += ti-tfp410.o
  obj-$(CONFIG_DRM_TI_TPD12S015) += ti-tpd12s015.o
 +obj-$(CONFIG_DRM_MIPI_DBI_SPI) += dbi-spi.o

mipi_dbi_spi.o would be nice...

quoted

  obj-$(CONFIG_DRM_NWL_MIPI_DSI) += nwl-dsi.o

  obj-y += analogix/
 diff --git a/drivers/gpu/drm/bridge/dbi-spi.c 
b/drivers/gpu/drm/bridge/dbi-spi.c
 new file mode 100644
 index 000000000000..1060b8f95fba
 --- /dev/null
 +++ b/drivers/gpu/drm/bridge/dbi-spi.c
 @@ -0,0 +1,261 @@
 +// SPDX-License-Identifier: GPL-2.0-or-later
 +/*
 + * MIPI Display Bus Interface (DBI) SPI support
 + *
 + * Copyright 2016 Noralf Trønnes
 + * Copyright 2020 Paul Cercueil [off-list ref]
 + */
 +
 +#include <linux/gpio/consumer.h>
 +#include <linux/module.h>
 +#include <linux/spi/spi.h>
 +
 +#include <drm/drm_mipi_dbi.h>
 +#include <drm/drm_mipi_dsi.h>
 +
 +#include <video/mipi_display.h>
 +
 +struct dbi_spi {
 +	struct mipi_dsi_host host;

It is very confusing that the mipi_dbi_spi driver uses a dsi_host.
It clashes in my head - and then reviewing it not easy.

 From now on read all "mipi_dsi_*" as a MIPI DSI/DBI API. Renaming the 
API means a treewide patchset that touches many many files...

quoted

 +	struct mipi_dsi_host_ops host_ops;

const?

quoted

 +
 +	struct spi_device *spi;
 +	struct gpio_desc *dc;
 +	struct mutex cmdlock;
 +
 +	unsigned int current_bus_type;
 +
 +	/**
 +	 * @tx_buf9: Buffer used for Option 1 9-bit conversion
 +	 */
 +	void *tx_buf9;
 +
 +	/**
 +	 * @tx_buf9_len: Size of tx_buf9.
 +	 */
 +	size_t tx_buf9_len;
 +};
 +
 +static inline struct dbi_spi *host_to_dbi_spi(struct mipi_dsi_host 
*host)
 +{
 +	return container_of(host, struct dbi_spi, host);
 +}
 +
 +static ssize_t dbi_spi1_transfer(struct mipi_dsi_host *host,
 +				 const struct mipi_dsi_msg *msg)
 +{
 +	struct dbi_spi *dbi = host_to_dbi_spi(host);
 +	struct spi_device *spi = dbi->spi;
 +	struct spi_transfer tr = {
 +		.bits_per_word = 9,
 +	};
 +	const u8 *src8 = msg->tx_buf;
 +	struct spi_message m;
 +	size_t max_chunk, chunk;
 +	size_t len = msg->tx_len;
 +	bool cmd_byte = true;
 +	unsigned int i;
 +	u16 *dst16;
 +	int ret;
 +
 +	tr.speed_hz = mipi_dbi_spi_cmd_max_speed(spi, len);
 +	dst16 = dbi->tx_buf9;
 +
 +	max_chunk = min(dbi->tx_buf9_len / 2, len);

Hmm, this looks not right. We limit the max_chunk to 8K here.
We learned the other day that we count in bytes.
OR did I miss something?

We want to extend 8-bit values into 16-bit values, and we have a 
X-bytes output buffer for that, so the maximum input buffer size we can 
use is (X/2).

This code is the original algorithm in drm_mipi_dbi.c, I didn't change 
anything here (safe for the fix that was merged a couple of days ago to 
drm-misc-fixes).

quoted

 +
 +	spi_message_init_with_transfers(&m, &tr, 1);
 +	tr.tx_buf = dst16;
 +
 +	while (len) {
 +		chunk = min(len, max_chunk);
 +
 +		for (i = 0; i < chunk; i++) {
 +			dst16[i] = *src8++;
 +
 +			/* Bit 9: 0 means command, 1 means data */
 +			if (!cmd_byte)
 +				dst16[i] |= BIT(9);
 +
 +			cmd_byte = false;
 +		}
 +
 +		tr.len = chunk * 2;
 +		len -= chunk;
 +
 +		ret = spi_sync(spi, &m);
 +		if (ret)
 +			return ret;
 +	}
 +
 +	return 0;
 +}
 +
 +static ssize_t dbi_spi3_transfer(struct mipi_dsi_host *host,
 +				 const struct mipi_dsi_msg *msg)
 +{
 +	struct dbi_spi *dbi = host_to_dbi_spi(host);
 +	struct spi_device *spi = dbi->spi;
 +	const u8 *buf = msg->tx_buf;
 +	unsigned int bpw = 8;
 +	u32 speed_hz;
 +	ssize_t ret;
 +
 +	/* for now we only support sending messages, not receiving */
 +	if (msg->rx_len)
 +		return -EINVAL;
 +
 +	gpiod_set_value_cansleep(dbi->dc, 0);
 +
 +	speed_hz = mipi_dbi_spi_cmd_max_speed(spi, 1);
 +	ret = mipi_dbi_spi_transfer(spi, speed_hz, 8, buf, 1);
 +	if (ret || msg->tx_len == 1)
 +		return ret;
 +
 +	if (buf[0] == MIPI_DCS_WRITE_MEMORY_START)
 +		bpw = 16;
 +
 +	gpiod_set_value_cansleep(dbi->dc, 1);
 +	speed_hz = mipi_dbi_spi_cmd_max_speed(spi, msg->tx_len - 1);
 +
 +	ret = mipi_dbi_spi_transfer(spi, speed_hz, bpw,
 +				    &buf[1], msg->tx_len - 1);
 +	if (ret)
 +		return ret;
 +
 +	return msg->tx_len;
 +}
 +
 +static ssize_t dbi_spi_transfer(struct mipi_dsi_host *host,
 +				const struct mipi_dsi_msg *msg)
 +{
 +	struct dbi_spi *dbi = host_to_dbi_spi(host);
 +
 +	switch (dbi->current_bus_type) {
 +	case MIPI_DEVICE_TYPE_DBI_SPI_MODE1:
 +		return dbi_spi1_transfer(host, msg);
 +	case MIPI_DEVICE_TYPE_DBI_SPI_MODE3:
 +		return dbi_spi3_transfer(host, msg);
 +	default:
 +		dev_err(&dbi->spi->dev, "Unknown transfer type\n");
 +		return -EINVAL;
 +	}
 +}
 +
 +static int dbi_spi_attach(struct mipi_dsi_host *host,
 +			  struct mipi_dsi_device *dsi)
 +{
 +	struct dbi_spi *dbi = host_to_dbi_spi(host);
 +
 +	dbi->current_bus_type = dsi->bus_type;
 +
 +	if (dbi->current_bus_type == MIPI_DEVICE_TYPE_DBI_SPI_MODE1) {
 +		dbi->tx_buf9_len = SZ_16K;
 +
 +		dbi->tx_buf9 = kmalloc(dbi->tx_buf9_len, GFP_KERNEL);
 +		if (!dbi->tx_buf9)
 +			return -ENOMEM;
 +	}
 +
 +	return 0;
 +}
 +
 +static int dbi_spi_detach(struct mipi_dsi_host *host,
 +			  struct mipi_dsi_device *dsi)
 +{
 +	struct dbi_spi *dbi = host_to_dbi_spi(host);
 +
 +	kfree(dbi->tx_buf9);
 +	dbi->tx_buf9_len = 0;
 +
 +	return 0; /* Nothing to do */
 +}
 +
 +static void dbi_spi_host_unregister(void *d)
 +{
 +	mipi_dsi_host_unregister(d);
 +}
 +
 +static int dbi_spi_probe(struct spi_device *spi)
 +{
 +	struct device *dev = &spi->dev;
 +	struct mipi_dsi_device_info info = { };
 +	struct mipi_dsi_device *dsi;
 +	struct dbi_spi *dbi;
 +	int ret;
 +
 +	dbi = devm_kzalloc(dev, sizeof(*dbi), GFP_KERNEL);
 +	if (!dbi)
 +		return -ENOMEM;
 +
 +	dbi->host.dev = dev;
 +	dbi->host.ops = &dbi->host_ops;
 +	dbi->spi = spi;
 +	spi_set_drvdata(spi, dbi);
 +
 +	dbi->dc = devm_gpiod_get_optional(dev, "dc", GPIOD_OUT_LOW);
 +	if (IS_ERR(dbi->dc)) {
 +		dev_err(dev, "Failed to get gpio 'dc'\n");
 +		return PTR_ERR(dbi->dc);
 +	}
 +
 +	if (spi_is_bpw_supported(spi, 9))
 +		dbi->host.bus_types |= MIPI_DEVICE_TYPE_DBI_SPI_MODE1;
 +	if (dbi->dc)
 +		dbi->host.bus_types |= MIPI_DEVICE_TYPE_DBI_SPI_MODE3;
 +
 +	if (!dbi->host.bus_types) {
 +		dev_err(dev, "Neither Type1 nor Type3 are supported\n");
 +		return -EINVAL;
 +	}
 +
 +	dbi->host_ops.transfer = dbi_spi_transfer;
 +	dbi->host_ops.attach = dbi_spi_attach;
 +	dbi->host_ops.detach = dbi_spi_detach;
 +
 +	mutex_init(&dbi->cmdlock);
 +
 +	ret = mipi_dsi_host_register(&dbi->host);
 +	if (ret) {
 +		dev_err(dev, "Unable to register DSI host\n");
 +		return ret;
 +	}
 +
 +	ret = devm_add_action_or_reset(dev, dbi_spi_host_unregister, 
&dbi->host);
 +	if (ret)
 +		return ret;
 +
 +	/*
 +	 * Register our own node as a MIPI DSI device.
 +	 * This ensures that the panel driver will be probed.
 +	 */
 +	info.channel = 0;
 +	info.node = of_node_get(dev->of_node);
 +
 +	dsi = mipi_dsi_device_register_full(&dbi->host, &info);
 +	if (IS_ERR(dsi)) {
 +		dev_err(dev, "Failed to add DSI device\n");
 +		return PTR_ERR(dsi);
 +	}
 +
 +	return 0;
 +}
 +
 +static const struct of_device_id dbi_spi_of_match[] = {
 +	{ .compatible = "adafruit,yx240qv29" },
 +	{ .compatible = "leadtek,ltk035c5444t-spi" },
 +	{ }

Would it be better with a fall-back compatible like:
mipi,dbi-spi.
So the nodes must includes this compatible to be registered with
this driver?

Ideally, it would be perfect, but unfortunately we cannot do that.

If a node has the following:
compatible = "adafruit,yx240qv29", "mipi-dbi-spi";

Then Linux will probe only with the first compatible string since it 
has a driver for it. It will use the fallback string only if no driver 
matches the first string.

-Paul

quoted

 +};
 +MODULE_DEVICE_TABLE(of, dbi_spi_of_match);
 +
 +static struct spi_driver dbi_spi_driver = {
 +	.driver = {
 +		.name = "dbi-spi",
 +		.of_match_table = dbi_spi_of_match,
 +	},
 +	.probe = dbi_spi_probe,
 +};
 +module_spi_driver(dbi_spi_driver);
 +
 +MODULE_DESCRIPTION("DBI SPI bus driver");
 +MODULE_AUTHOR("Paul Cercueil [off-list ref]");
 +MODULE_LICENSE("GPL");
 --
 2.27.0