drm: Add helper for DP++ adaptors

Add a helper which aids in the identification of DP dual mode
(aka. DP++) adaptors. There are several types of adaptors
specified: type 1 DVI, type 1 HDMI, type 2 DVI, type 2 HDMI

Type 1 adaptors have a max TMDS clock limit of 165MHz, type 2 adaptors
may go as high as 300MHz and they provide a register informing the
source device what the actual limit is. Supposedly also type 1 adaptors
may optionally implement this register. This TMDS clock limit is the
main reason why we need to identify these adaptors.

Type 1 adaptors provide access to their internal registers and the sink
DDC bus through I2C. Type 2 adaptors provide this access both via I2C
and I2C-over-AUX. A type 2 source device may choose to implement either
of these methods. If a source device implements the I2C-over-AUX
method, then the driver will obviously need specific support for such
adaptors since the port is driven like an HDMI port, but DDC
communication happes over the AUX channel.

This helper should be enough to identify the adaptor type (some
type 1 DVI adaptors may be a slight exception) and the maximum TMDS
clock limit. Another feature that may be available is control over
the TMDS output buffers on the adaptor, possibly allowing for some
power saving when the TMDS link is down.

Other user controllable features that may be available in the adaptors
are downstream i2c bus speed control when using i2c-over-aux, and
some control over the CEC pin. I chose not to provide any helper
functions for those since I have no use for them in i915 at this time.
The rest of the registers in the adaptor are mostly just information,
eg. IEEE OUI, hardware and firmware revision, etc.

v2: Pass adaptor type to helper functions to ease driver implementation
    Fix a bunch of typoes (Paulo)
    Add DRM_DP_DUAL_MODE_UNKNOWN for the case where we don't (yet) know
    the type (Paulo)
    Reject 0x00 and 0xff DP_DUAL_MODE_MAX_TMDS_CLOCK values (Paulo)
    Adjust drm_dp_dual_mode_detect() type2 vs. type1 detection to
    ease future LSPCON enabling
    Remove the unused DP_DUAL_MODE_LAST_RESERVED define
v3: Fix kernel doc function argument descriptions (Jani)
    s/NONE/UNKNOWN/ in drm_dp_dual_mode_detect() docs
    Add kernel doc for enum drm_dp_dual_mode_type
    Actually build the docs
    Fix more typoes
v4: Adjust code indentation of type2 adaptor detection (Shashank)
    Add debug messages for failurs cases (Shashank)
v5: EXPORT_SYMBOL(drm_dp_dual_mode_read) (Paulo)

Cc: stable@vger.kernel.org
Cc: Tore Anderson <tore@fud.no>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com> (v4)
Link: http://patchwork.freedesktop.org/patch/msgid/1462542412-25533-1-git-send-email-ville.syrjala@linux.intel.com

2 files changed, 367 insertions, 1 deletions

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 6eb94fc561dc..22228ef50f36 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -23,7 +23,7 @@ drm-$(CONFIG_AGP) += drm_agpsupport.o
 
 drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
 		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o \
-		drm_kms_helper_common.o
+		drm_kms_helper_common.o drm_dp_dual_mode_helper.o
 
 drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
 drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
new file mode 100644
index 000000000000..a7b2a751f6fe
--- /dev/null
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -0,0 +1,366 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ *
+ * 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, sublicense,
+ * 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 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 NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) 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/errno.h>
+#include <linux/export.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <drm/drm_dp_dual_mode_helper.h>
+#include <drm/drmP.h>
+
+/**
+ * DOC: dp dual mode helpers
+ *
+ * Helper functions to deal with DP dual mode (aka. DP++) adaptors.
+ *
+ * Type 1:
+ * Adaptor registers (if any) and the sink DDC bus may be accessed via I2C.
+ *
+ * Type 2:
+ * Adaptor registers and sink DDC bus can be accessed either via I2C or
+ * I2C-over-AUX. Source devices may choose to implement either of these
+ * access methods.
+ */
+
+#define DP_DUAL_MODE_SLAVE_ADDRESS 0x40
+
+/**
+ * drm_dp_dual_mode_read - Read from the DP dual mode adaptor register(s)
+ * @adapter: I2C adapter for the DDC bus
+ * @offset: register offset
+ * @buffer: buffer for return data
+ * @size: sizo of the buffer
+ *
+ * Reads @size bytes from the DP dual mode adaptor registers
+ * starting at @offset.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+ssize_t drm_dp_dual_mode_read(struct i2c_adapter *adapter,
+			      u8 offset, void *buffer, size_t size)
+{
+	struct i2c_msg msgs[] = {
+		{
+			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
+			.flags = 0,
+			.len = 1,
+			.buf = &offset,
+		},
+		{
+			.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
+			.flags = I2C_M_RD,
+			.len = size,
+			.buf = buffer,
+		},
+	};
+	int ret;
+
+	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_dp_dual_mode_read);
+
+/**
+ * drm_dp_dual_mode_write - Write to the DP dual mode adaptor register(s)
+ * @adapter: I2C adapter for the DDC bus
+ * @offset: register offset
+ * @buffer: buffer for write data
+ * @size: sizo of the buffer
+ *
+ * Writes @size bytes to the DP dual mode adaptor registers
+ * starting at @offset.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+ssize_t drm_dp_dual_mode_write(struct i2c_adapter *adapter,
+			       u8 offset, const void *buffer, size_t size)
+{
+	struct i2c_msg msg = {
+		.addr = DP_DUAL_MODE_SLAVE_ADDRESS,
+		.flags = 0,
+		.len = 1 + size,
+		.buf = NULL,
+	};
+	void *data;
+	int ret;
+
+	data = kmalloc(msg.len, GFP_TEMPORARY);
+	if (!data)
+		return -ENOMEM;
+
+	msg.buf = data;
+
+	memcpy(data, &offset, 1);
+	memcpy(data + 1, buffer, size);
+
+	ret = i2c_transfer(adapter, &msg, 1);
+
+	kfree(data);
+
+	if (ret < 0)
+		return ret;
+	if (ret != 1)
+		return -EPROTO;
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_write);
+
+static bool is_hdmi_adaptor(const char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN])
+{
+	static const char dp_dual_mode_hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] =
+		"DP-HDMI ADAPTOR\x04";
+
+	return memcmp(hdmi_id, dp_dual_mode_hdmi_id,
+		      sizeof(dp_dual_mode_hdmi_id)) == 0;
+}
+
+static bool is_type2_adaptor(uint8_t adaptor_id)
+{
+	return adaptor_id == (DP_DUAL_MODE_TYPE_TYPE2 |
+			      DP_DUAL_MODE_REV_TYPE2);
+}
+
+/**
+ * drm_dp_dual_mode_detect - Identify the DP dual mode adaptor
+ * @adapter: I2C adapter for the DDC bus
+ *
+ * Attempt to identify the type of the DP dual mode adaptor used.
+ *
+ * Note that when the answer is @DRM_DP_DUAL_MODE_UNKNOWN it's not
+ * certain whether we're dealing with a native HDMI port or
+ * a type 1 DVI dual mode adaptor. The driver will have to use
+ * some other hardware/driver specific mechanism to make that
+ * distinction.
+ *
+ * Returns:
+ * The type of the DP dual mode adaptor used
+ */
+enum drm_dp_dual_mode_type drm_dp_dual_mode_detect(struct i2c_adapter *adapter)
+{
+	char hdmi_id[DP_DUAL_MODE_HDMI_ID_LEN] = {};
+	uint8_t adaptor_id = 0x00;
+	ssize_t ret;
+
+	/*
+	 * Let's see if the adaptor is there the by reading the
+	 * HDMI ID registers.
+	 *
+	 * Note that type 1 DVI adaptors are not required to implemnt
+	 * any registers, and that presents a problem for detection.
+	 * If the i2c transfer is nacked, we may or may not be dealing
+	 * with a type 1 DVI adaptor. Some other mechanism of detecting
+	 * the presence of the adaptor is required. One way would be
+	 * to check the state of the CONFIG1 pin, Another method would
+	 * simply require the driver to know whether the port is a DP++
+	 * port or a native HDMI port. Both of these methods are entirely
+	 * hardware/driver specific so we can't deal with them here.
+	 */
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_HDMI_ID,
+				    hdmi_id, sizeof(hdmi_id));
+	if (ret)
+		return DRM_DP_DUAL_MODE_UNKNOWN;
+
+	/*
+	 * Sigh. Some (maybe all?) type 1 adaptors are broken and ack
+	 * the offset but ignore it, and instead they just always return
+	 * data from the start of the HDMI ID buffer. So for a broken
+	 * type 1 HDMI adaptor a single byte read will always give us
+	 * 0x44, and for a type 1 DVI adaptor it should give 0x00
+	 * (assuming it implements any registers). Fortunately neither
+	 * of those values will match the type 2 signature of the
+	 * DP_DUAL_MODE_ADAPTOR_ID register so we can proceed with
+	 * the type 2 adaptor detection safely even in the presence
+	 * of broken type 1 adaptors.
+	 */
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_ADAPTOR_ID,
+				    &adaptor_id, sizeof(adaptor_id));
+	if (ret == 0) {
+		if (is_type2_adaptor(adaptor_id)) {
+			if (is_hdmi_adaptor(hdmi_id))
+				return DRM_DP_DUAL_MODE_TYPE2_HDMI;
+			else
+				return DRM_DP_DUAL_MODE_TYPE2_DVI;
+		}
+	}
+
+	if (is_hdmi_adaptor(hdmi_id))
+		return DRM_DP_DUAL_MODE_TYPE1_HDMI;
+	else
+		return DRM_DP_DUAL_MODE_TYPE1_DVI;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_detect);
+
+/**
+ * drm_dp_dual_mode_max_tmds_clock - Max TMDS clock for DP dual mode adaptor
+ * @type: DP dual mode adaptor type
+ * @adapter: I2C adapter for the DDC bus
+ *
+ * Determine the max TMDS clock the adaptor supports based on the
+ * type of the dual mode adaptor and the DP_DUAL_MODE_MAX_TMDS_CLOCK
+ * register (on type2 adaptors). As some type 1 adaptors have
+ * problems with registers (see comments in drm_dp_dual_mode_detect())
+ * we don't read the register on those, instead we simply assume
+ * a 165 MHz limit based on the specification.
+ *
+ * Returns:
+ * Maximum supported TMDS clock rate for the DP dual mode adaptor in kHz.
+ */
+int drm_dp_dual_mode_max_tmds_clock(enum drm_dp_dual_mode_type type,
+				    struct i2c_adapter *adapter)
+{
+	uint8_t max_tmds_clock;
+	ssize_t ret;
+
+	/* native HDMI so no limit */
+	if (type == DRM_DP_DUAL_MODE_NONE)
+		return 0;
+
+	/*
+	 * Type 1 adaptors are limited to 165MHz
+	 * Type 2 adaptors can tells us their limit
+	 */
+	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
+		return 165000;
+
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
+				    &max_tmds_clock, sizeof(max_tmds_clock));
+	if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff) {
+		DRM_DEBUG_KMS("Failed to query max TMDS clock\n");
+		return 165000;
+	}
+
+	return max_tmds_clock * 5000 / 2;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_max_tmds_clock);
+
+/**
+ * drm_dp_dual_mode_get_tmds_output - Get the state of the TMDS output buffers in the DP dual mode adaptor
+ * @type: DP dual mode adaptor type
+ * @adapter: I2C adapter for the DDC bus
+ * @enabled: current state of the TMDS output buffers
+ *
+ * Get the state of the TMDS output buffers in the adaptor. For
+ * type2 adaptors this is queried from the DP_DUAL_MODE_TMDS_OEN
+ * register. As some type 1 adaptors have problems with registers
+ * (see comments in drm_dp_dual_mode_detect()) we don't read the
+ * register on those, instead we simply assume that the buffers
+ * are always enabled.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+int drm_dp_dual_mode_get_tmds_output(enum drm_dp_dual_mode_type type,
+				     struct i2c_adapter *adapter,
+				     bool *enabled)
+{
+	uint8_t tmds_oen;
+	ssize_t ret;
+
+	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) {
+		*enabled = true;
+		return 0;
+	}
+
+	ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN,
+				    &tmds_oen, sizeof(tmds_oen));
+	if (ret) {
+		DRM_DEBUG_KMS("Failed to query state of TMDS output buffers\n");
+		return ret;
+	}
+
+	*enabled = !(tmds_oen & DP_DUAL_MODE_TMDS_DISABLE);
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_get_tmds_output);
+
+/**
+ * drm_dp_dual_mode_set_tmds_output - Enable/disable TMDS output buffers in the DP dual mode adaptor
+ * @type: DP dual mode adaptor type
+ * @adapter: I2C adapter for the DDC bus
+ * @enable: enable (as opposed to disable) the TMDS output buffers
+ *
+ * Set the state of the TMDS output buffers in the adaptor. For
+ * type2 this is set via the DP_DUAL_MODE_TMDS_OEN register. As
+ * some type 1 adaptors have problems with registers (see comments
+ * in drm_dp_dual_mode_detect()) we avoid touching the register,
+ * making this function a no-op on type 1 adaptors.
+ *
+ * Returns:
+ * 0 on success, negative error code on failure
+ */
+int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type,
+				     struct i2c_adapter *adapter, bool enable)
+{
+	uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE;
+	ssize_t ret;
+
+	if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
+		return 0;
+
+	ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN,
+				     &tmds_oen, sizeof(tmds_oen));
+	if (ret) {
+		DRM_DEBUG_KMS("Failed to %s TMDS output buffers\n",
+			      enable ? "enable" : "disable");
+		return ret;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output);
+
+/**
+ * drm_dp_get_dual_mode_type_name - Get the name of the DP dual mode adaptor type as a string
+ * @type: DP dual mode adaptor type
+ *
+ * Returns:
+ * String representation of the DP dual mode adaptor type
+ */
+const char *drm_dp_get_dual_mode_type_name(enum drm_dp_dual_mode_type type)
+{
+	switch (type) {
+	case DRM_DP_DUAL_MODE_NONE:
+		return "none";
+	case DRM_DP_DUAL_MODE_TYPE1_DVI:
+		return "type 1 DVI";
+	case DRM_DP_DUAL_MODE_TYPE1_HDMI:
+		return "type 1 HDMI";
+	case DRM_DP_DUAL_MODE_TYPE2_DVI:
+		return "type 2 DVI";
+	case DRM_DP_DUAL_MODE_TYPE2_HDMI:
+		return "type 2 HDMI";
+	default:
+		WARN_ON(type != DRM_DP_DUAL_MODE_UNKNOWN);
+		return "unknown";
+	}
+}
+EXPORT_SYMBOL(drm_dp_get_dual_mode_type_name);