diff options
Diffstat (limited to 'libgamma_internal_parse_edid.c')
| -rw-r--r-- | libgamma_internal_parse_edid.c | 99 |
1 files changed, 99 insertions, 0 deletions
diff --git a/libgamma_internal_parse_edid.c b/libgamma_internal_parse_edid.c new file mode 100644 index 0000000..aa1b87c --- /dev/null +++ b/libgamma_internal_parse_edid.c @@ -0,0 +1,99 @@ +/* See LICENSE file for copyright and license details. */ +#include "common.h" + + +/* + * EDID structure revision 1.1: + * http://en.wikipedia.org/w/index.php?title=Extended_display_identification_data&oldid=46295569 + * + * EDID structure revision 1.3: + * http://en.wikipedia.org/wiki/Extended_display_identification_data + */ + + +/** + * Parse the EDID of a monitor + * + * @param this Instance of a data structure to fill with the information about the EDID; + * it must contain the EDID and its length + * @param fields OR:ed identifiers for the information about the EDID that should be parsed; + * fields that do not have to do with EDID are ignored + * @return Non-zero on error + */ +int +libgamma_internal_parse_edid(libgamma_crtc_information_t *restrict this, int32_t fields) +{ +#define __test_version(edid, major, minor_min, minor_max)\ + ((edid)[18] == (major) && (minor_min) <= (edid)[19] && (edid)[19] <= (minor_max)) +#define __m(value)\ + (this->edid[index++] != (value)) + + int error = 0, checksum = 0; + size_t i, index = 0; + + /* If the length of the EDID is not 128 bytes, we know that it is not of EDID + structure revision 1.0–1.3, and thus we do not support it. Additionally + this make sure we do not do segmentation violation on the next test. */ + if (this->edid_length != 128) + error = LIBGAMMA_EDID_LENGTH_UNSUPPORTED; + /* Check that the magic number of that of the EDID structure. */ + else if (__m(0x00) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0xFF) || __m(0x00)) + error = LIBGAMMA_EDID_WRONG_MAGIC_NUMBER; + /* Check that EDID structure revision 1.1–1.3 is used, those are the only + version we support. EDID structure revision 1.3 is also by far the most + commonly use revision and it is currently the newest revision. We know + that parsing works for both revision 1.1 and revision 1.3, because of + this we assume it is also correct for revision 1.2. However, we are not + assuming this for revision 1.0 which appeared in August 1994 and was + replaced by revision 1.1 in April 1996. */ + else if (!__test_version(this->edid, 1, 1, 3)) + error = LIBGAMMA_EDID_REVISION_UNSUPPORTED; + + /* If we have encountered an error, report it for the fields that require + the EDID to be parsed. Note that it is not stored for the EDID field + itself because it is not considered an error just because we do not + support the used version. */ + this->width_mm_edid_error = this->height_mm_edid_error = this->gamma_error = error; + + /* Retrieve the size of the viewport. This is done even if it is not + requested because it is not worth it branch. */ + this->width_mm_edid = (size_t)this->edid[21] * 10; + this->height_mm_edid = (size_t)this->edid[22] * 10; + + /* Retrieve the monitor's gamma characteristics. */ + if ((fields & LIBGAMMA_CRTC_INFO_GAMMA) && !error) { + if (this->edid[23] == 0xFF) { + /* If the gamma charactistics is FFh (3,55) it should be interpreted as not specified. */ + this->gamma_error = LIBGAMMA_GAMMA_NOT_SPECIFIED; + } else { + this->gamma_blue = (float)((int)this->edid[23] + 100) / 100.f; + this->gamma_red = this->gamma_green = this->gamma_blue; + } + } + + /* If not error has occurred, calculate and test the checksum. + It is not considered an error that the gamma characteristics + is left unspecified in the EDID. */ + if (!error) + for (i = 0; i < this->edid_length; i++) + checksum += (int)this->edid[i]; + /* The checksum should be zero. */ + if (checksum & 255) { + /* Store the error in all fields that require the EDID to be parsed, + as well as the EDID field itself. */ + error = LIBGAMMA_EDID_CHECKSUM_ERROR; + this->edid_error = this->width_mm_edid_error = this->height_mm_edid_error = error; + /* If the gamma characteristics is not specified, that is kept, + and the checksum error is augmented. */ + this->gamma_error = this->gamma_error == LIBGAMMA_GAMMA_NOT_SPECIFIED + ? LIBGAMMA_GAMMA_NOT_SPECIFIED_AND_EDID_CHECKSUM_ERROR : error; + } + + /* Return whether or not we encountered an error or if + the gamma characteristics was requested but is not + specified in the monitor's EDID. */ + return error | this->gamma_error; + +#undef __m +#undef __test_version +} |