[PATCH v2] drm/tegra: hdmi: Setup audio only if configured

[Thierry Reding]

From: Thierry Reding <treding at nvidia.com>

The audio configuration is only valid if the HDMI codec has been
properly set up. Do not attempt to set up audio before that happens
because it causes a division by zero.

Note that this is only problematic on Tegra20 and Tegra30. Later chips
implement the division instructions which return zero when dividing by
zero and don't throw an exception.

Fixes: db5adf4d6dce ("drm/tegra: hdmi: Fix audio to work with any pixel clock rate")
Reported-by: Marcel Ziswiler <marcel.ziswiler at toradex.com>
Signed-off-by: Thierry Reding <treding at nvidia.com>
---
Changes in v2:
- setup audio at ->enable() time if it has been configured, otherwise
  audio playback needs to be restarted after the display goes through
  a disable/enable cycle

 drivers/gpu/drm/tegra/hdmi.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/tegra/hdmi.c b/drivers/gpu/drm/tegra/hdmi.c
index 47c55974756d..d23c4bfde790 100644
--- a/drivers/gpu/drm/tegra/hdmi.c
+++ b/drivers/gpu/drm/tegra/hdmi.c
@@ -1260,9 +1260,15 @@ static void tegra_hdmi_encoder_enable(struct drm_encoder *encoder)
 
 	hdmi->dvi = !tegra_output_is_hdmi(output);
 	if (!hdmi->dvi) {
-		err = tegra_hdmi_setup_audio(hdmi);
-		if (err < 0)
-			hdmi->dvi = true;
+		/*
+		 * Make sure that the audio format has been configured before
+		 * enabling audio, otherwise we may try to divide by zero.
+		*/
+		if (hdmi->format.sample_rate > 0) {
+			err = tegra_hdmi_setup_audio(hdmi);
+			if (err < 0)
+				hdmi->dvi = true;
+		}
 	}
 
 	if (hdmi->config->has_hda)
-- 
2.21.0