[PATCH v3 14/16] drm/panel-simple-edp: Fix "prepare_to_enable" if panel doesn't handle HPD

From: Douglas Anderson
Date: Wed Sep 01 2021 - 16:21:53 EST

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@xxxxxxxxxxxx>

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);