[PATCH v3 09/12] drm/bridge: ti-sn65dsi86: Fail aux transfers right away if not powered

[Douglas Anderson <dianders@chromium.org>]

If the bridge (and panel) haven't been powered on then AUX transfers
just won't work. Let's just fail them instantly.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
If the patch ("drm/panel: panel-simple: Use runtime pm to avoid
excessive unprepare / prepare") is accepted then we could consider
actually powering the panel on instead of failing the
transfer. However, without that patch the overhead would just be too
much since we need to do several AUX transfers for a single EDID read
and powering up and down each time would just be too much.

Changes in v3:
- ("Fail aux transfers right away if not powered") split out for v3.

 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 543590801a8e..a76cac93cb46 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -896,6 +896,13 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	int ret;
 	u8 addr_len[SN_AUX_LENGTH_REG + 1 - SN_AUX_ADDR_19_16_REG];
 
+	/*
+	 * Things just won't work if the panel isn't powered. Return failure
+	 * right away.
+	 */
+	if (!pdata->pre_enabled)
+		return -EIO;
+
 	if (len > SN_AUX_MAX_PAYLOAD_BYTES)
 		return -EINVAL;
 
-- 
2.31.0.208.g409f899ff0-goog