tools: Add a simple tool to read/write/decode dpcd registers

This tool serves as a wrapper around the constructs provided by the drm_dpcd_aux_dev kernel module by working on the /dev/drm_dp_aux[n] devices created by the kernel module.
It supports reading and writing dpcd registers on the connected aux channels.
In the follow-up patch, support for decoding these registers will be added to facilate debugging panel related issues.

v2: (Fixes by Rodrigo but no functional changes yet):
- Indentations, Typo, Missed spaces
- Removing mentioning to decode and spec that is not implemented yet.
- Add Makefile.sources back
- Missed s/printf/igt_warn

v3:
- Addres DK's review comments from v2 above.
- Squash Rodrigo's file handling unification patch.
- Make count, offset and device id optional.

v4:
- Better error handling and refactoring.

Suggested-by Dhinakaran Pandiyan <[email protected]>

Signed-off-by Tarun Vyas <[email protected]>

Signed-off-by Rodrigo Vivi <[email protected]>

---
 tools/Makefile.sources |   1 +
 tools/dpcd_reg.c       | 273
+++++++++++++++++++++++++++++++++++++++++++++++++ tools/meson.build      | 
 1 +
 3 files changed, 275 insertions(+)
 create mode 100644 tools/dpcd_reg.c

tools/Makefile.sources +1 -0

index abd23a0f..50706f41 100644
@@ -7,6 +7,7 @@ noinst_PROGRAMS =		\
 
 tools_prog_lists =		\
 	igt_stats		\
+	dpcd_reg		\
 	intel_audio_dump	\
 	intel_reg		\
 	intel_backlight		\

tools/dpcd_reg.c new file +5 -0

new file mode 100644
index 00000000..8419b9e5
@@ -0,0 +1,273 @@
+/*
+ * Copyright © 2018 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 (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 NONINFRINGEMENT. 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.
+ *
+ * DPCD register read/write tool
+ * This tool wraps around DRM_DP_AUX_DEV module to provide DPCD register read + * and write, so CONFIG_DRM_DP_AUX_DEV needs to be set.
+ */

tools/dpcd_reg.c new file +38 -0

+
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <limits.h>
+#include <stdbool.h>
+
+#define MAX_DP_OFFSET	0xfffff
+#define DRM_AUX_MINORS	256
+
+const char aux_dev[] = "/dev/drm_dp_aux";
+
+struct dpcd_data {
+	int devid;
+	int file_op;
+	uint32_t offset;
+	enum command {
+		INVALID = -1,
+		READ = 2,
+		WRITE,
+	} cmd;
+	size_t count;
+	uint8_t val;
+};
+
+static void print_usage(void)
+{
+	printf("Usage: dpcd_reg [OPTION ...] COMMAND\n\n");
+	printf("COMMAND is one of:\n");
+	printf("  read:		Read [count] bytes dpcd reg at an offset\n");
+	printf("  write:	Write a dpcd reg at an offset\n\n");
+	printf("Options for the above COMMANDS are\n");
+	printf(" --device=DEVID		Aux device id, as listed in

/dev/drm_dp_aux_dev[n]." + "Defaults to 0. Upper limit -

tools/dpcd_reg.c new file +3 -0

+	printf(" --offset=REG_ADDR	DPCD register offset in hex. Defaults to 0x0"
+					"Upper limit - 0xfffff\n");
+	printf(" --count=BYTES		For reads, specify number of bytes to be read

from" + " the offset. Defaults to 1\n");

tools/dpcd_reg.c new file +9 -0

+	printf(" --value		For writes, specify a hex value to be written"
+					"Upper limit - 0xff\n\n");
+
+	printf(" --help: print the usage\n");
+}
+
+static inline bool strtol_err_util(char *endptr, long *val)
+{
+	return (*endptr != '\0' || *val < 0 || (*val == LONG_MAX && errno ==

ERANGE)) \ + ? true : false;

tools/dpcd_reg.c new file +13 -0

+}
+
+static int parse_opts(struct dpcd_data *dpcd, int argc, char **argv)
+{
+	int ret, vflag = 0;
+	long temp;
+	char *endptr;
+
+	struct option longopts[] = {
+		{ "count",	required_argument,	NULL,		'c' },
+		{ "device",	required_argument,	NULL,		'd' },
+		{ "help",	no_argument,		NULL,		'h' },
+		{ "offset",	required_argument,	NULL,		'o' },

tools/dpcd_reg.c new file +15 -0

+				print_usage();
+				return ERANGE;
+			}
+			dpcd->devid = temp;
+			break;
+		case 'h':
+			printf("DPCD register read and write tool\n\n");
+			printf("This tool requires CONFIG_DRM_DP_AUX_CHARDEV\n"
+				"to be set in the kernel config.\n\n");
+			print_usage();
+			exit(EXIT_SUCCESS);
+		case 'o':
+			temp = strtol(optarg, &endptr, 16);
+			if (strtol_err_util(endptr, &temp) || temp > MAX_DP_OFFSET) {
+				fprintf(stderr, "--offset argument is

invalid/negative/out-of-range\n"); + print_usage();

tools/dpcd_reg.c new file +15 -0

+				print_usage();
+				return ERANGE;
+			}
+			dpcd->val = temp;
+			break;
+		/* Command parsing */
+		case 1:
+			if (strcmp(optarg, "read") == 0) {
+				temp = READ;
+			} else if (strcmp(optarg, "write") == 0) {
+				temp = WRITE;
+				dpcd->file_op = O_WRONLY;
+			} else {
+				fprintf(stderr, "Unrecognized command\n");
+				print_usage();

tools/dpcd_reg.c new file +31 -0

+		default:
+			fprintf(stderr, "Argument of  -%c is invalid\n", optopt);
+			print_usage();
+			return EXIT_FAILURE;
+		}
+	}
+
+	if ((dpcd->count + dpcd->offset) > (MAX_DP_OFFSET + 1)) {
+		fprintf(stderr, "Out of bounds. Count + Offset <= 0x100000\n");
+		return ERANGE;
+	}
+
+	if ((dpcd->cmd == WRITE) && (vflag != 'v')) {
+		fprintf(stderr, "Write value is missing\n");
+		print_usage();
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}
+
+static int dpcd_read(int fd, uint32_t offset, size_t count)
+{
+	int ret = EXIT_SUCCESS, pret, i;
+	uint8_t *buf = calloc(count, sizeof(uint8_t));
+
+	if (!buf) {
+		fprintf(stderr, "Can't allocate read buffer\n");
+		return ENOMEM;
+	}
+

tools/dpcd_reg.c new file +8 -0

+	for (i = 0; i < pret; i++)
+		printf(" %02x", *(buf + i));
+	printf("\n");
+
+out:
+	free(buf);
+	return ret;
+}

tools/dpcd_reg.c new file +28 -0

+	}
+
+	return ret;
+}
+
+int main(int argc, char **argv)
+{
+	char dev_name[20];
+	int ret, fd;
+
+	struct dpcd_data dpcd = {
+		.devid = 0,
+		.file_op = O_RDONLY,
+		.offset = 0x0,
+		.cmd = INVALID,
+		.count = 1,
+	};
+
+	if((ret = parse_opts(&dpcd, argc, argv)) != EXIT_SUCCESS)
+		return ret;
+
+	snprintf(dev_name, strlen(aux_dev) + 4, "%s%d", aux_dev, dpcd.devid);
+
+	fd = open(dev_name, dpcd.file_op);
+	if (fd < 0) {
+		fprintf(stderr, "Failed to open %s aux device - error: %s\n", dev_name,
+			strerror(errno));
+		return errno;

tools/dpcd_reg.c new file +11 -0

+	default:
+		fprintf(stderr, "Please specify a command: read/write.\n");
+		print_usage();
+		ret = EXIT_FAILURE;
+		break;
+	}
+
+	close(fd);
+
+	return ret;
+}

tools/meson.build +0 -0

index e4517d66..79f36aa9 100644