linux/drivers/gpu/drm/drm_scdc_helper.c

/*
 * Copyright (c) 2015 NVIDIA Corporation. All rights reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sub license,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial portions
 * of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#include <linux/slab.h>

#include <drm/drm_scdc_helper.h>

/**
 * DOC: scdc helpers
 *
 * Status and Control Data Channel (SCDC) is a mechanism introduced by the
 * HDMI 2.0 specification. It is a point-to-point protocol that allows the
 * HDMI source and HDMI sink to exchange data. The same I2C interface that
 * is used to access EDID serves as the transport mechanism for SCDC.
 */

#define SCDC_I2C_SLAVE_ADDRESS 0x54

/**
 * drm_scdc_read - read a block of data from SCDC
 * @adapter: I2C controller
 * @offset: start offset of block to read
 * @buffer: return location for the block to read
 * @size: size of the block to read
 *
 * Reads a block of data from SCDC, starting at a given offset.
 *
 * Returns:
 * 0 on success, negative error code on failure.
 */
ssize_t drm_scdc_read(struct i2c_adapter *adapter, u8 offset, void *buffer,
		      size_t size)
{
	int ret;
	struct i2c_msg msgs[2] = {
		{
			.addr = SCDC_I2C_SLAVE_ADDRESS,
			.flags = 0,
			.len = 1,
			.buf = &offset,
		}, {
			.addr = SCDC_I2C_SLAVE_ADDRESS,
			.flags = I2C_M_RD,
			.len = size,
			.buf = buffer,
		}
	};

	ret = i2c_transfer(adapter, msgs, ARRAY_SIZE(msgs));
	if (ret < 0)
		return ret;
	if (ret != ARRAY_SIZE(msgs))
		return -EPROTO;

	return 0;
}
EXPORT_SYMBOL(drm_scdc_read);

/**
 * drm_scdc_write - write a block of data to SCDC
 * @adapter: I2C controller
 * @offset: start offset of block to write
 * @buffer: block of data to write
 * @size: size of the block to write
 *
 * Writes a block of data to SCDC, starting at a given offset.
 *
 * Returns:
 * 0 on success, negative error code on failure.
 */
ssize_t drm_scdc_write(struct i2c_adapter *adapter, u8 offset,
		       const void *buffer, size_t size)
{
	struct i2c_msg msg = {
		.addr = SCDC_I2C_SLAVE_ADDRESS,
		.flags = 0,
		.len = 1 + size,
		.buf = NULL,
	};
	void *data;
	int err;

	data = kmalloc(1 + size, GFP_TEMPORARY);
	if (!data)
		return -ENOMEM;

	msg.buf = data;

	memcpy(data, &offset, sizeof(offset));
	memcpy(data + 1, buffer, size);

	err = i2c_transfer(adapter, &msg, 1);

	kfree(data);

	if (err < 0)
		return err;
	if (err != 1)
		return -EPROTO;

	return 0;
}
EXPORT_SYMBOL(drm_scdc_write);