From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: abhinavk@codeaurora.org
Cc: aravindh@codeaurora.org, seanpaul@chromium.org,
chandanu@codeaurora.org, dri-devel@lists.freedesktop.org
Subject: Re: Question on 640x480 @ 72fps
Date: Fri, 31 Aug 2018 14:06:27 +0300 [thread overview]
Message-ID: <20180831110627.GR5565@intel.com> (raw)
In-Reply-To: <8b761109203a732857b18811fb3f0212@codeaurora.org>
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
--
Ville Syrjälä
Intel
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
next prev parent reply other threads:[~2018-08-31 11:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-31 2:32 Question on 640x480 @ 72fps abhinavk
2018-08-31 11:06 ` Ville Syrjälä [this message]
2018-08-31 12:23 ` Sean Paul
2018-08-31 18:07 ` Abhinav Kumar
2018-09-03 7:45 ` Daniel Vetter
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180831110627.GR5565@intel.com \
--to=ville.syrjala@linux.intel.com \
--cc=abhinavk@codeaurora.org \
--cc=aravindh@codeaurora.org \
--cc=chandanu@codeaurora.org \
--cc=dri-devel@lists.freedesktop.org \
--cc=seanpaul@chromium.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.