drivers/gpu/drm/sitronix/st7571-i2c.c

Source file repositories/reference/linux-study-clean/drivers/gpu/drm/sitronix/st7571-i2c.c

File Facts

System
Linux kernel
Corpus path
drivers/gpu/drm/sitronix/st7571-i2c.c
Extension
.c
Size
4558 bytes
Lines
159
Domain
Driver Families
Bucket
drivers/gpu
Inferred role
Driver Families: implementation source
Status
source implementation candidate

Why This File Exists

Repeatable hardware-adapter layer. Deep compatibility for every driver is out of scope; this atlas records patterns, probe lifecycles, bus glue, IRQ/DMA usage, and links back to core abstractions.

Dependency Surface

Detected Declarations

Annotated Snippet

struct st7571_i2c_transport {
	struct i2c_client *client;

	/*
	 * Depending on the hardware design, the acknowledge signal may be hard to
	 * recognize as a valid logic "0" level.
	 * Therefor, ignore NAK if possible to stay compatible with most hardware designs
	 * and off-the-shelf panels out there.
	 *
	 * From section 6.4 MICROPOCESSOR INTERFACE section in the datasheet:
	 *
	 * "By connecting SDA_OUT to SDA_IN externally, the SDA line becomes fully
	 * I2C interface compatible.
	 * Separating acknowledge-output from serial data
	 * input is advantageous for chip-on-glass (COG) applications. In COG
	 * applications, the ITO resistance and the pull-up resistor will form a
	 * voltage  divider, which affects acknowledge-signal level. Larger ITO
	 * resistance will raise the acknowledged-signal level and system cannot
	 * recognize this level as a valid logic “0” level. By separating SDA_IN from
	 * SDA_OUT, the IC can be used in a mode that ignores the acknowledge-bit.
	 * For applications which check acknowledge-bit, it is necessary to minimize
	 * the ITO resistance of the SDA_OUT trace to guarantee a valid low level."
	 *
	 */
	bool ignore_nak;
};

static int st7571_i2c_regmap_write(void *context, const void *data, size_t count)
{
	struct st7571_i2c_transport *t = context;
	int ret;

	struct i2c_msg msg = {
		.addr = t->client->addr,
		.flags = t->ignore_nak ? I2C_M_IGNORE_NAK : 0,
		.len = count,
		.buf = (u8 *)data
	};

	ret = i2c_transfer(t->client->adapter, &msg, 1);

	/*
	 * Unfortunately, there is no way to check if the transfer failed because of
	 * a NAK or something else as I2C bus drivers use different return values for NAK.
	 *
	 * However, if the transfer fails and ignore_nak is set, we know it is an error.
	 */
	if (ret < 0 && t->ignore_nak)
		return ret;

	return 0;
}

/* The st7571 driver does not read registers but regmap expects a .read */
static int st7571_i2c_regmap_read(void *context, const void *reg_buf,
				  size_t reg_size, void *val_buf, size_t val_size)
{
	return -EOPNOTSUPP;
}

static const struct regmap_bus st7571_i2c_regmap_bus = {
	.read = st7571_i2c_regmap_read,
	.write = st7571_i2c_regmap_write,
};

static const struct regmap_config st7571_i2c_regmap_config = {
	.reg_bits = 8,
	.val_bits = 8,
	.use_single_write = true,
};

static int st7571_i2c_probe(struct i2c_client *client)
{
	struct st7571_device *st7571;
	struct st7571_i2c_transport *t;
	struct regmap *regmap;

	t = devm_kzalloc(&client->dev, sizeof(*t), GFP_KERNEL);
	if (!t)
		return -ENOMEM;

	t->client = client;

	/*
	 * The hardware design could make it hard to detect a NAK on the I2C bus.
	 * If the adapter does not support protocol mangling do
	 * not set the I2C_M_IGNORE_NAK flag at the expense * of possible
	 * cruft in the logs.
	 */
	if (i2c_check_functionality(client->adapter, I2C_FUNC_PROTOCOL_MANGLING))

Annotation

Implementation Notes