[PATCH v4 3/5] drm/bridge: it6505: guard against zero channel count in audio infoframe

it6505->audio.channel_count is zero from allocation until either DP
link training has run once (it6505_variable_config()) or a valid
hw_params call has cached a channel count. it6505_enable_audio() can
be reached before either of those has happened, e.g. from the
audio-FIFO-error IRQ, which is unmasked unconditionally at poweron.
it6505_enable_audio_infoframe() then indexes the 8-entry
audio_info_ca[] table with channel_count - 1, an out-of-bounds stack
read when channel_count is still 0.

Bail out of it6505_enable_audio_infoframe() when channel_count is not
yet known instead of indexing with it.

While here, fix the debug print in it6505_audio_setup_hw_params(): on
the invalid-channel-count path it logged the previously cached
channel_count instead of the actually-rejected params->cea.channels.

Fixes: b5c84a9edcd4 ("drm/bridge: add it6505 driver")
Signed-off-by: Daniel Golle <[email protected]>
Reviewed-by: Chen-Yu Tsai <[email protected]>
---
v4: no changes

v3: new patch, split out to fix pre-existing bugs flagged by
    automated review of v2's audio series; needed before that series
    starts exercising the audio-FIFO-error IRQ path in a
    configuration where channel_count == 0 is actually reachable.

 drivers/gpu/drm/bridge/ite-it6505.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/ite-it6505.c b/drivers/gpu/drm/bridge/ite-it6505.c
index 2a8298ee6c03..443ea5579744 100644
--- a/drivers/gpu/drm/bridge/ite-it6505.c
+++ b/drivers/gpu/drm/bridge/ite-it6505.c
@@ -1575,6 +1575,9 @@ static void it6505_enable_audio_infoframe(struct it6505 *it6505)
 	struct device *dev = it6505->dev;
 	u8 audio_info_ca[] = { 0x00, 0x00, 0x01, 0x03, 0x07, 0x0B, 0x0F, 0x1F };
 
+	if (!it6505->audio.channel_count)
+		return;
+
 	DRM_DEV_DEBUG_DRIVER(dev, "infoframe channel_allocation:0x%02x",
 			     audio_info_ca[it6505->audio.channel_count - 1]);
 
@@ -2991,7 +2994,7 @@ static int __maybe_unused it6505_audio_setup_hw_params(struct it6505 *it6505,
 
 	if (params->cea.channels <= 1 || params->cea.channels > 8) {
 		DRM_DEV_DEBUG_DRIVER(dev, "channel number: %d not support",
-				     it6505->audio.channel_count);
+				     params->cea.channels);
 		return -EINVAL;
 	}
 
-- 
2.55.0