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Date: Mon, 27 Jul 2020 23:10:30 +0200
From: Paul Cercueil <paul@crapouillou.net>
Subject: Re: [PATCH 3/6] drm/bridge: Add SPI DBI host driver
To: Sam Ravnborg <sam@ravnborg.org>
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Hi Sam,

Le lun. 27 juil. 2020 =E0 22:31, Sam Ravnborg <sam@ravnborg.org> a =

=E9crit :
> Hi Paul.
> =

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

>>  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 :)

>> =

>>  Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>  ---
>>   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?
> =

>>   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-$(CONFIG_DRM_I2C_ADV7511) +=3D adv7511/
>>   obj-$(CONFIG_DRM_TI_SN65DSI86) +=3D ti-sn65dsi86.o
>>   obj-$(CONFIG_DRM_TI_TFP410) +=3D ti-tfp410.o
>>   obj-$(CONFIG_DRM_TI_TPD12S015) +=3D ti-tpd12s015.o
>>  +obj-$(CONFIG_DRM_MIPI_DBI_SPI) +=3D dbi-spi.o
> mipi_dbi_spi.o would be nice...
> =

>>   obj-$(CONFIG_DRM_NWL_MIPI_DSI) +=3D nwl-dsi.o
>> =

>>   obj-y +=3D 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 Tr=F8nnes
>>  + * Copyright 2020 Paul Cercueil <paul@crapouillou.net>
>>  + */
>>  +
>>  +#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...

> =

>>  +	struct mipi_dsi_host_ops host_ops;
> const?
>>  +
>>  +	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 =3D host_to_dbi_spi(host);
>>  +	struct spi_device *spi =3D dbi->spi;
>>  +	struct spi_transfer tr =3D {
>>  +		.bits_per_word =3D 9,
>>  +	};
>>  +	const u8 *src8 =3D msg->tx_buf;
>>  +	struct spi_message m;
>>  +	size_t max_chunk, chunk;
>>  +	size_t len =3D msg->tx_len;
>>  +	bool cmd_byte =3D true;
>>  +	unsigned int i;
>>  +	u16 *dst16;
>>  +	int ret;
>>  +
>>  +	tr.speed_hz =3D mipi_dbi_spi_cmd_max_speed(spi, len);
>>  +	dst16 =3D dbi->tx_buf9;
>>  +
>>  +	max_chunk =3D 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).

> =

>>  +
>>  +	spi_message_init_with_transfers(&m, &tr, 1);
>>  +	tr.tx_buf =3D dst16;
>>  +
>>  +	while (len) {
>>  +		chunk =3D min(len, max_chunk);
>>  +
>>  +		for (i =3D 0; i < chunk; i++) {
>>  +			dst16[i] =3D *src8++;
>>  +
>>  +			/* Bit 9: 0 means command, 1 means data */
>>  +			if (!cmd_byte)
>>  +				dst16[i] |=3D BIT(9);
>>  +
>>  +			cmd_byte =3D false;
>>  +		}
>>  +
>>  +		tr.len =3D chunk * 2;
>>  +		len -=3D chunk;
>>  +
>>  +		ret =3D 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 =3D host_to_dbi_spi(host);
>>  +	struct spi_device *spi =3D dbi->spi;
>>  +	const u8 *buf =3D msg->tx_buf;
>>  +	unsigned int bpw =3D 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 =3D mipi_dbi_spi_cmd_max_speed(spi, 1);
>>  +	ret =3D mipi_dbi_spi_transfer(spi, speed_hz, 8, buf, 1);
>>  +	if (ret || msg->tx_len =3D=3D 1)
>>  +		return ret;
>>  +
>>  +	if (buf[0] =3D=3D MIPI_DCS_WRITE_MEMORY_START)
>>  +		bpw =3D 16;
>>  +
>>  +	gpiod_set_value_cansleep(dbi->dc, 1);
>>  +	speed_hz =3D mipi_dbi_spi_cmd_max_speed(spi, msg->tx_len - 1);
>>  +
>>  +	ret =3D 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 =3D 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 =3D host_to_dbi_spi(host);
>>  +
>>  +	dbi->current_bus_type =3D dsi->bus_type;
>>  +
>>  +	if (dbi->current_bus_type =3D=3D MIPI_DEVICE_TYPE_DBI_SPI_MODE1) {
>>  +		dbi->tx_buf9_len =3D SZ_16K;
>>  +
>>  +		dbi->tx_buf9 =3D 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 =3D host_to_dbi_spi(host);
>>  +
>>  +	kfree(dbi->tx_buf9);
>>  +	dbi->tx_buf9_len =3D 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 =3D &spi->dev;
>>  +	struct mipi_dsi_device_info info =3D { };
>>  +	struct mipi_dsi_device *dsi;
>>  +	struct dbi_spi *dbi;
>>  +	int ret;
>>  +
>>  +	dbi =3D devm_kzalloc(dev, sizeof(*dbi), GFP_KERNEL);
>>  +	if (!dbi)
>>  +		return -ENOMEM;
>>  +
>>  +	dbi->host.dev =3D dev;
>>  +	dbi->host.ops =3D &dbi->host_ops;
>>  +	dbi->spi =3D spi;
>>  +	spi_set_drvdata(spi, dbi);
>>  +
>>  +	dbi->dc =3D 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 |=3D MIPI_DEVICE_TYPE_DBI_SPI_MODE1;
>>  +	if (dbi->dc)
>>  +		dbi->host.bus_types |=3D 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 =3D dbi_spi_transfer;
>>  +	dbi->host_ops.attach =3D dbi_spi_attach;
>>  +	dbi->host_ops.detach =3D dbi_spi_detach;
>>  +
>>  +	mutex_init(&dbi->cmdlock);
>>  +
>>  +	ret =3D mipi_dsi_host_register(&dbi->host);
>>  +	if (ret) {
>>  +		dev_err(dev, "Unable to register DSI host\n");
>>  +		return ret;
>>  +	}
>>  +
>>  +	ret =3D 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 =3D 0;
>>  +	info.node =3D of_node_get(dev->of_node);
>>  +
>>  +	dsi =3D 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[] =3D {
>>  +	{ .compatible =3D "adafruit,yx240qv29" },
>>  +	{ .compatible =3D "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 =3D "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

> =

>>  +};
>>  +MODULE_DEVICE_TABLE(of, dbi_spi_of_match);
>>  +
>>  +static struct spi_driver dbi_spi_driver =3D {
>>  +	.driver =3D {
>>  +		.name =3D "dbi-spi",
>>  +		.of_match_table =3D dbi_spi_of_match,
>>  +	},
>>  +	.probe =3D dbi_spi_probe,
>>  +};
>>  +module_spi_driver(dbi_spi_driver);
>>  +
>>  +MODULE_DESCRIPTION("DBI SPI bus driver");
>>  +MODULE_AUTHOR("Paul Cercueil <paul@crapouillou.net>");
>>  +MODULE_LICENSE("GPL");
>>  --
>>  2.27.0


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