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

Tarun Vyas
2018-09-21T20:36:07Z

On Thu, Sep 20, 2018 at 11:12:49PM -0700, Dhinakaran Pandiyan wrote:
> 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?
>
Forgot to remove it.
> > +#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)
>
Will modify.
> > +
> > +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' ?
>
Will do
> > + 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.
>
Will do.
> > +}
> > +
> > +static int dpcd_read(int fd, const uint32_t offset, size_t count)
> const is not needed as the arguments are passed by value.
>
Will remove it.
> > +{
> > + int ret, i;
> > + void *buf = calloc(count, sizeof(uint8_t));
> uint8_t *buf ?
>
Heh, yea.
> > +
> > + 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.
>
Ok
> > + ret = errno;
> > + goto out;
> > + } else
> } else {
>
> > + ret = EXIT_SUCCESS;
> Intialize ret and get rid of the else block?
>
Aye
> > +
> > + 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.
Will modify
> > + 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?
>
I wanted to init INVALID with an -ve value. Just following the trend from intel_reg.
> > + 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.
>
>
I didnt wan't to rely on initializing the *write value* with an invalid , so based on the vflag, we'll know if the write value was ever set or not and error out accordingly.
getopt_long will only complain if the user supplies --value option but no argument with it. If the user chooses to completely skip the --value option then we won't know.
> > -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.
>
Hmm, makes sense.
> > + 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.
>
My idea was to use the vflag to check if --value option was used at all or not.
> > + val = (uint8_t) strtoul(optarg, NULL, 16);
> Reject values greater than 0xff?
>
uint8_t cast should truncate everything, but yea, I'll explicitly check for anything > 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.
>
Alright
> > + 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?
>
Oh no, the %c is the format specifier. So, if count, devid, offset etc. are passed w/o an argument,
then this will print something like "The -v option of tools/dpcd_reg requires an argument",
for the value argument, in this case, or -d for the devid argument and so on.
> > + 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,
Ok.
> > + 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?
>
Will modify.
> > +
> > + 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
>
Right
> > + default:
> > + fprintf(stderr, "Please specify a command: read/write. See usage\n");
> Remove "See usage"
>
> > + close(fd);
> There's another close() below.
>
print_usage was exiting so the other close() wouldnt be called. But with the removal of exit from print_usage, this will change.
> > + 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.
>
Thanks for the review :)
> -DK