nmk_i2c_xfer(9)

🌸 NAME 🌸

okay so bestie, nmk_i2c_xfer(9) — from the Kernel API Manual — is literally the I2C transfer function used by the kernel framework. iconic. 💖

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✨ SYNOPSIS ✨

int nmk_i2c_xfer (struct i2c_adapter *i2c_adap , struct i2c_msg msgs[] ,
int num_msgs );

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🎀 ARGUMENTS 🎀

• i2c_adap — adapter pointer to the controller, aka the whole vibe check for which controller we're talking to. 🦋
• msgs — pointer to data to be written. yes, that's the description; no cap. 💅
• num_msgs — number of messages to be executed. slay the count. ✨

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🦋 DESCRIPTION 🦋

this is the function called by the generic kernel i2c_transfer or i2c_smbus...() API calls. and lowkey important: this code is protected by the semaphore set in the kernel i2c_transfer function. periodt. 👑

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💅 NOTE 💅

💖 READ TRANSFER 💖

we impose a restriction, bestie: the first message has to be the index message for any read transaction. fr fr. 😭

• a no index is coded as '0',
• 2byte big endian index is coded as '3' !!! msg[0].buf holds the actual index.

this is compatible with generic messages of smbus emulator that send a one byte index.

example: an I2C transaction to read 2 bytes from index 0:

idx = 0; msg[0].addr = client->addr; msg[0].flags = 0x0; msg[0].len = 1; msg[0].buf = idx;

msg[1].addr = client->addr; msg[1].flags = I2C_M_RD; msg[1].len = 2;
msg[1].buf = rd_buff i2c_transfer(adap, msg, 2);

🦋 WRITE TRANSFER 🦋

the I2C standard interface interprets all data as payload. if you want to emulate an SMBUS write transaction, put the index as first byte(or first and second) in the payload. 🎀

example: an I2C transaction to write 2 bytes from index 1:

wr_buff[0] = 0x1; wr_buff[1] = 0x23; wr_buff[2] = 0x46; msg[0].flags = 0x0; msg[0].len = 3; msg[0].buf = wr_buff; i2c_transfer(adap, msg, 1);

to read or write a block of data (multiple bytes) using SMBUS emulation, please use the i2c_smbus_read_i2c_block_data or i2c_smbus_write_i2c_block_data API. that's the move. 💅✨

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👑 SEE ALSO 👑

kernel file ./drivers/i2c/busses/i2c-nomadik.c struct i2c_vendor_data(9), struct i2c_nmk_client(9), struct nmk_i2c_dev(9), flush_i2c_fifo(9), disable_all_interrupts(9), clear_all_interrupts(9), init_hw(9), load_i2c_mcr_reg(9), setup_i2c_controller(9), read_i2c(9), write_i2c(9), nmk_i2c_xfer_one(9), disable_interrupts(9), i2c_irq_handler(9). go read, bestie. 🌈

🫶 source/version: ./drivers/i2c/busses · date: October 2026 · page: nmk_i2c_xfer(9) — bye bestie, go slay those transfers 💖✨