Re: [igt-dev] [PATCH i-g-t v3] tools: Add a simple tool to read/write/decode dpcd registers

Dhinakaran Pandiyan
2018-09-21T06:12:58Z

On Friday, September 14, 2018 4:57:02 PM PDT Tarun Vyas wrote:
> 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.
>
> Suggested-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
> Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
> tools/Makefile.sources | 1 +
> tools/dpcd_reg.c | 213
> +++++++++++++++++++++++++++++++++++++++++++++++++ tools/meson.build |
> 1 +
> 3 files changed, 215 insertions(+)
> create mode 100644 tools/dpcd_reg.c
>
> diff --git a/tools/Makefile.sources b/tools/Makefile.sources
> index abd23a0f..50706f41 100644
> --- a/tools/Makefile.sources
> +++ b/tools/Makefile.sources
> @@ -7,6 +7,7 @@ noinst_PROGRAMS = \
>
> tools_prog_lists = \
> igt_stats \
> + dpcd_reg \
> intel_audio_dump \
> intel_reg \
> intel_backlight \
> diff --git a/tools/dpcd_reg.c b/tools/dpcd_reg.c
> new file mode 100644
> index 00000000..cd9fed4f
> --- /dev/null
> +++ b/tools/dpcd_reg.c
> @@ -0,0 +1,213 @@
> +/*
> + * 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.
> + */
> +
> +#include "igt_core.h"
What's the dependency on igt_core here?

> +#include <errno.h>
> +#include <fcntl.h>
> +#include <limits.h>
> +
> +#define MAX_OFFSET 0xf02ff
I think we should be able to allow allow up to the max limit of 0xfffff (DP
1.4 section 2.9.3)

> +
> +const char aux_dev[] = "/dev/drm_dp_aux";
> +
> +static void print_usage(char *tool, int exit_code)
> +{
> + 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");
I think it would look better to print the above lines only when --help/-h was
passed. Move this under case 'h' ?

> + printf("Usage: %s [OPTION ...] COMMAND\n\n", tool);
> + 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\n");
> + printf(" --offset=REG_ADDR DPCD register offset in hex. Defaults to
> 0x00\n"); + printf(" --count=BYTES For reads, specify number of bytes to
> be read from" + "the offset. Defaults to 1\n");
> + printf(" --val For writes, specify a hex value to be written\n\n");
> +
> + printf(" --help: print the usage\n");
> +
> + exit(exit_code);
Modify the callers so that you don't have to exit from a print function.

> +}
> +
> +static int dpcd_read(int fd, const uint32_t offset, size_t count)
const is not needed as the arguments are passed by value.

> +{
> + int ret, i;
> + void *buf = calloc(count, sizeof(uint8_t));
uint8_t *buf ?

> +
> + if (!buf) {
> + fprintf(stderr, "Can't allocate read buffer\n");
> + return ENOMEM;
> + }
> +
> + ret = pread(fd, buf, count, offset);
> + if (ret != count) {
> + fprintf(stderr, "Failed to read - %s\n", strerror(errno));
Print ret too? If the number of bytes read were lower, errno won't be set.

> + ret = errno;
> + goto out;
> + } else
} else {

> + ret = EXIT_SUCCESS;
Intialize ret and get rid of the else block?

> +
> + printf("Read %zu byte(s) starting at offset %x\n\n", count, offset);
Print this debug message only if the expected number of bytes weren't read and
something like printf("Read %zu bytes, expected %zu\n");

printf("0x"); to clarify that the printed values are in hex.
> + for (i = 0; i < count; i++)
> + printf(" %02x", *(((uint8_t *)(buf)) + i));
You can avoid typecasting if you define the array as type uint8_t

> + printf("\n");
> +
> +out:
> + free(buf);
> + return ret;
> +}
> +
> +static int dpcd_write(int fd, const uint32_t offset, const uint8_t val)
const isn't needed.

> +{
> + int ret;
> +
> + ret = pwrite(fd, (const void *)&val, sizeof(uint8_t), offset);
> + if (ret < 0) {
> + fprintf(stderr, "Failed to write - %s\n", strerror(errno));
Same as above, print number of bytes written in case of error.

> + return errno;
> + } else
> + return EXIT_SUCCESS;
You could avoid 'else' here.

> +}
> +
> +int main(int argc, char **argv)
> +{
> + char dev_name[20];
> + int ret, devid, fd, vflag = 0;
> + uint32_t offset;
> + uint8_t val;
> + size_t count;
> + int file_op = O_RDONLY;
> +
> + enum command {
> + INV = -1,
> + READ = 2,
Any reason to not use the value compiler generates?

> + WRITE,
> + } cmd = INV;
> +
> + struct option longopts[] = {
> + { "count", required_argument, NULL, 'c' },
> + { "device", required_argument, NULL, 'd' },
> + { "help", no_argument, NULL, 'h' },
> + { "offset", required_argument, NULL, 'o' },
> + { "value", required_argument, &vflag, 'v' },
> + { 0 }
> + };
> +
> + devid = 0, count = 1, offset = 0x0;
> +
> + while ((ret = getopt_long(argc, argv, "-:c:d:h:o:", longopts, NULL)) !=
Any reason to leave out the option -v ? And '-h' shouldn't need an argument.

> -1) { + switch (ret) {
> + case 'c':
> + count = strtoul(optarg, NULL, 10);
With strtol() you should be able reject all negative args and make use of the
second argument to reject invalid numbers.

> + if (count == ULONG_MAX) {
> + fprintf(stderr, "Count argument too big\n");
> + exit(ERANGE);
> + }
> + break;
> + case 'd':
> + devid = strtoul(optarg, NULL, 10);
Same here, strtol() to reject negatives and use **endptr to fail on invalid
numbers.

> + if (devid == ULONG_MAX) {
> + fprintf(stderr, "Devid argument too big\n");

> + exit(ERANGE);
> + }
> + break;
> + case 'h':
> + print_usage(argv[0], EXIT_SUCCESS);
> + break;
> + case 'o':
> + offset = strtoul(optarg, NULL, 16);
Same comment as for 'd'. You might also want to check if errno is set.

> + if (offset > MAX_OFFSET) {
> + fprintf(stderr, "Offset should be <= 0xf02ff\n");
> + exit(ERANGE);
> + }
> + break;
> + case 0:
> + if (vflag == 'v' && optarg)
I didn't get why &vflag had to be used.

> + val = (uint8_t) strtoul(optarg, NULL, 16);
Reject values greater than 0xff?

> + break;
> + /* Command parsing */
> + case 1:
> + if (strcmp(optarg, "read") == 0) {
> + cmd = READ;
> + } else if (strcmp(optarg, "write") == 0) {
> + cmd = WRITE;
> + file_op = O_WRONLY;
> + }
> + break;
} else {
and exit here? or fall through to default block by re-arranging the blocks.

> + case ':':
> + fprintf(stderr, "The -%c option of %s requires an argument\n",
> + optopt, argv[0]);

Prints "The -c option of tools/dpcd_reg requires an argument", is that what
you intended? Skip printing the tool path?

> + print_usage(argv[0], EXIT_FAILURE);
> + case '?':
> + default:
> + fprintf(stderr, "%s - option %c is invalid\n", argv[0],
> + optopt);
> + print_usage(argv[0], EXIT_FAILURE);
> + }
> + }
> +
> + if ((count + offset) > (MAX_OFFSET + 1)) {
> + fprintf(stderr, "Out of bounds. Count + Offset <= 0xf0300\n");
> + exit(ERANGE);
> + }
> +
> + if ((cmd == WRITE) && (vflag != 'v')) {
> + fprintf(stderr, "Write value is missing\n");
> + print_usage(argv[0], EXIT_FAILURE);
> + }
> +
> + memset(dev_name, '\0', 20);
Not needed as snprintf includes the null byte,
> + snprintf(dev_name, strlen(aux_dev) + 3, "%s%d", aux_dev, devid);
Allows a max of 99 for devid, which should be okay but define a macro and
reject opt args greater than that?

> +
> + fd = open(dev_name, file_op);
> + if (fd < 0) {
> + fprintf(stderr, "Failed to open %s aux device - error: %s\n", dev_name,
> + strerror(errno));
> + return errno;
> + }
> +
> + switch (cmd) {
> + case READ:
> + ret = dpcd_read(fd, offset, count);
> + break;
> + case WRITE:
> + ret = dpcd_write(fd, offset, val);
> + break;
> + case INV:
INVALID is easier to understand

> + default:
> + fprintf(stderr, "Please specify a command: read/write. See usage\n");
Remove "See usage"

> + close(fd);
There's another close() below.

> + print_usage(argv[0], EXIT_FAILURE);
> + }
> +
> + close(fd);
> +
> + return ret;
> +}
> diff --git a/tools/meson.build b/tools/meson.build
> index e4517d66..79f36aa9 100644
> --- a/tools/meson.build
> +++ b/tools/meson.build
> @@ -36,6 +36,7 @@ tools_progs = [
> 'intel_watermark',
> 'intel_gem_info',
> 'intel_gvtg_test',
> + 'dpcd_reg',
> ]
> tool_deps = igt_deps

Thanks for working on this. The tool looks good overall,. just needs some
minor polishing.

-DK