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SubjectRe: [PATCH 3/6] drm/bridge: Add SPI DBI host driver
Hi Sam,

Le lun. 27 juil. 2020 à 22:31, Sam Ravnborg <sam@ravnborg.org> a
écrit :
> 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-$(CONFIG_DRM_I2C_ADV7511) += adv7511/
>> obj-$(CONFIG_DRM_TI_SN65DSI86) += ti-sn65dsi86.o
>> obj-$(CONFIG_DRM_TI_TFP410) += ti-tfp410.o
>> obj-$(CONFIG_DRM_TI_TPD12S015) += ti-tpd12s015.o
>> +obj-$(CONFIG_DRM_MIPI_DBI_SPI) += dbi-spi.o
> mipi_dbi_spi.o would be nice...
>
>> obj-$(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 <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 = 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).

>
>> +
>> + 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

>
>> +};
>> +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 <paul@crapouillou.net>");
>> +MODULE_LICENSE("GPL");
>> --
>> 2.27.0


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