linux-kernel - Re: [RFC][PATCH 1/2] drm/probe-helper: Add mode_valid check to drm_crtc_helper

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Date:   Tue, 14 Feb 2017 20:32:46 +0000
From:   Daniel Stone <daniel@...ishbar.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        Rob Clark <robdclark@...il.com>,
        Xinliang Liu <xinliang.liu@...aro.org>,
        Xinliang Liu <z.liuxinliang@...ilicon.com>,
        Rongrong Zou <zourongrong@...il.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        Archit Taneja <architt@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 1/2] drm/probe-helper: Add mode_valid check to drm_crtc_helper_funcs

Hi John,

On 14 February 2017 at 19:25, John Stultz <john.stultz@...aro.org> wrote:
> +static enum drm_mode_status
> +drm_connector_check_crtc_modes(struct drm_connector *connector,
> +                              struct drm_display_mode *mode)
> +{
> +       struct drm_device *dev = connector->dev;
> +       const struct drm_crtc_helper_funcs *crtc_funcs;
> +       struct drm_crtc *c;
> +
> +       if (mode->status != MODE_OK)
> +               return mode->status;
> +
> +       /* Check all the crtcs on a connector to make sure the mode is valid */
> +       drm_for_each_crtc(c, dev) {
> +               crtc_funcs = c->helper_private;
> +               if (crtc_funcs && crtc_funcs->mode_valid)
> +                       mode->status = crtc_funcs->mode_valid(c, mode);
> +               if (mode->status != MODE_OK)
> +                       break;
> +       }
> +       return mode->status;
> +}

Hm, that's unfortunate: it limits the mode list for every connector,
to those which are supported by every single CRTC. So if you have one
CRTC serving low-res LVDS, and another serving higher-res HDMI,
suddenly you can't get bigger modes on HDMI. The idea seems sound
enough, but a little more nuance might be good ...

Cheers,
Daniel