drm/rockchip: analogix_dp: Refuse to enable PSR if panel doesn't support it

There's no point in enabling PSR when the panel doesn't support it.

This also avoids a problem when PSR gets enabled when a CRTC is being
disabled, because sometimes in that situation the DSP_HOLD_VALID_INTR
interrupt on which we wait will never arrive. This was observed on
RK3288 with a panel without PSR (veyron-jaq Chromebook).

It's very easy to reproduce by running the kms_rmfb test in IGT a few
times.

Cc: Yakir Yang <ykk@rock-chips.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1474639600-30090-2-git-send-email-tomeu.vizoso@collabora.com

drivers/gpu/drm/rockchip/analogix_dp-rockchip.c

@@ -85,6 +85,9 @@ static void analogix_dp_psr_set(struct drm_encoder *encoder, bool enabled)
 	struct rockchip_dp_device *dp = to_dp(encoder);
 	unsigned long flags;
 
+	if (!analogix_dp_psr_supported(dp->dev))
+		return;
+
 	dev_dbg(dp->dev, "%s PSR...\n", enabled ? "Entry" : "Exit");
 
 	spin_lock_irqsave(&dp->psr_lock, flags);