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    Subject[PATCH v3 14/16] drm/panel-simple-edp: Fix "prepare_to_enable" if panel doesn't handle HPD
    Date
    While cleaning up the descriptions of the delay for eDP panels I
    realized that we'd have a bug if any panels need the
    "prepare_to_enable" but HPD handling isn't happening in the panel
    driver. Let's put in a stopgap to at least make us not violate
    timings. This is not perfectly optimal but trying to do better is
    hard. At the moment only 2 panels specify this delay and only 30 ms is
    at stake. These panels are also currently hooked up with "hpd-gpios"
    so effectively this "fix" is just a theoretical fix and won't actually
    do anything for any devices currently supported in mainline.

    Signed-off-by: Douglas Anderson <dianders@chromium.org>
    ---

    Changes in v3:
    - Fix "prepare_to_enable" patch new for v3.

    drivers/gpu/drm/panel/panel-simple-edp.c | 24 ++++++++++++++++++++++--
    1 file changed, 22 insertions(+), 2 deletions(-)

    diff --git a/drivers/gpu/drm/panel/panel-simple-edp.c b/drivers/gpu/drm/panel/panel-simple-edp.c
    index 762589ef66c3..5d58dc25ddf5 100644
    --- a/drivers/gpu/drm/panel/panel-simple-edp.c
    +++ b/drivers/gpu/drm/panel/panel-simple-edp.c
    @@ -508,12 +508,32 @@ static int panel_edp_prepare(struct drm_panel *panel)
    static int panel_edp_enable(struct drm_panel *panel)
    {
    struct panel_edp *p = to_panel_edp(panel);
    + unsigned int delay;

    if (p->enabled)
    return 0;

    - if (p->desc->delay.enable)
    - msleep(p->desc->delay.enable);
    + delay = p->desc->delay.enable;
    +
    + /*
    + * If there is a "prepare_to_enable" delay then that's supposed to be
    + * the delay from HPD going high until we can turn the backlight on.
    + * However, we can only count this if HPD is handled by the panel
    + * driver, not if it goes to a dedicated pin on the controller.
    + * If we aren't handling the HPD pin ourselves then the best we
    + * can do is assume that HPD went high immediately before we were
    + * called (and link training took zero time).
    + *
    + * NOTE: if we ever end up in this "if" statement then we're
    + * guaranteed that the panel_edp_wait() call below will do no delay.
    + * It already handles that case, though, so we don't need any special
    + * code for it.
    + */
    + if (p->desc->delay.prepare_to_enable && !p->hpd_gpio && !p->no_hpd)
    + delay = max(delay, p->desc->delay.prepare_to_enable);
    +
    + if (delay)
    + msleep(delay);

    panel_edp_wait(p->prepared_time, p->desc->delay.prepare_to_enable);

    --
    2.33.0.259.gc128427fd7-goog
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