On Thu, Aug 30, 2018 at 07:32:58PM -0700, abhinavk@codeaurora.org wrote:
Hello
During one of our internal tests, we ran into an issue where the calculated refresh rate for the mode using the drm_mode_vrefresh() API doesnt match the theoretical value due to rounding.
552 { DRM_MODE("640x480", DRM_MODE_TYPE_DRIVER, 31500, 640, 664, 553 704, 832, 0, 480, 489, 492, 520, 0, 554 DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC) }, /* 640x480@72Hz */
int drm_mode_vrefresh(const struct drm_display_mode *mode) { int refresh = 0;
if (mode->vrefresh > 0) refresh = mode->vrefresh; else if (mode->htotal > 0 && mode->vtotal > 0) { unsigned int num, den; num = mode->clock * 1000; den = mode->htotal * mode->vtotal; if (mode->flags & DRM_MODE_FLAG_INTERLACE) num *= 2; if (mode->flags & DRM_MODE_FLAG_DBLSCAN) den *= 2; if (mode->vscan > 1) den *= mode->vscan; refresh = DIV_ROUND_CLOSEST(num, den); } return refresh;} EXPORT_SYMBOL(drm_mode_vrefresh);
As per the math of this API, the vrefresh comes up to 72.8 fps ( 31500 * 1000 ) / (832 * 520) .
Hence this gets rounded to 73fps.
However as per the spec, this mode should have the vrefresh as 72fps.
Why should anyone care if it gets rounded differently?
So to satisfy that, we must round-down in this function. That might break other modes though.
Do you have any suggestions on how to fix-up this mode ? Shall we just directly specify the vrefresh in the edid_est_modes[] and drm_dmt_modes[] static array?
I can submit a PATCH based on the approach we agree on here.
Thanks
Abhinav _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel