[PATCH v4] drm/connector: hdmi: Fix writing Dynamic Range Mastering infoframes

[Derek Foreman <derek.foreman@collabora.com>]

The largest infoframe we create is the DRM (Dynamic Range Mastering)
infoframe which is 26 bytes + a 4 byte header, for a total of 30
bytes.

With HDMI_MAX_INFOFRAME_SIZE set to 29 bytes, as it is now, we
allocate too little space to pack a DRM infoframe in
write_device_infoframe(), leading to an ENOSPC return from
hdmi_infoframe_pack(), and never calling the connector's
write_infoframe() vfunc.

Instead of having HDMI_MAX_INFOFRAME_SIZE defined in two places,
replace HDMI_MAX_INFOFRAME_SIZE with HDMI_INFOFRAME_SIZE(MAX) and make
MAX 27 bytes - which is defined by the HDMI specification to be the
largest infoframe payload.

Fixes: f378b77227bc ("drm/connector: hdmi: Add Infoframes generation")
Fixes: c602e4959a0c ("drm/connector: hdmi: Create Infoframe DebugFS entries")

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>
---
 drivers/gpu/drm/display/drm_hdmi_state_helper.c | 4 +---
 drivers/gpu/drm/drm_debugfs.c                   | 4 +---
 include/linux/hdmi.h                            | 9 +++++++++
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
index 7854820089ec..feb7a3a75981 100644
--- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c
+++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c
@@ -521,8 +521,6 @@ int drm_atomic_helper_connector_hdmi_check(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_atomic_helper_connector_hdmi_check);
 
-#define HDMI_MAX_INFOFRAME_SIZE		29
-
 static int clear_device_infoframe(struct drm_connector *connector,
 				  enum hdmi_infoframe_type type)
 {
@@ -563,7 +561,7 @@ static int write_device_infoframe(struct drm_connector *connector,
 {
 	const struct drm_connector_hdmi_funcs *funcs = connector->hdmi.funcs;
 	struct drm_device *dev = connector->dev;
-	u8 buffer[HDMI_MAX_INFOFRAME_SIZE];
+	u8 buffer[HDMI_INFOFRAME_SIZE(MAX)];
 	int ret;
 	int len;
 
diff --git a/drivers/gpu/drm/drm_debugfs.c b/drivers/gpu/drm/drm_debugfs.c
index 6b239a24f1df..9d3e6dd68810 100644
--- a/drivers/gpu/drm/drm_debugfs.c
+++ b/drivers/gpu/drm/drm_debugfs.c
@@ -520,8 +520,6 @@ static const struct file_operations drm_connector_fops = {
 	.write = connector_write
 };
 
-#define HDMI_MAX_INFOFRAME_SIZE		29
-
 static ssize_t
 audio_infoframe_read(struct file *filp, char __user *ubuf, size_t count, loff_t *ppos)
 {
@@ -579,7 +577,7 @@ static ssize_t _f##_read_infoframe(struct file *filp, \
 	struct drm_connector *connector; \
 	union hdmi_infoframe *frame; \
 	struct drm_device *dev; \
-	u8 buf[HDMI_MAX_INFOFRAME_SIZE]; \
+	u8 buf[HDMI_INFOFRAME_SIZE(MAX)]; \
 	ssize_t len = 0; \
 	\
 	connector = filp->private_data; \
diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
index 3bb87bf6bc65..455f855bc084 100644
--- a/include/linux/hdmi.h
+++ b/include/linux/hdmi.h
@@ -59,6 +59,15 @@ enum hdmi_infoframe_type {
 #define HDMI_DRM_INFOFRAME_SIZE    26
 #define HDMI_VENDOR_INFOFRAME_SIZE  4
 
+/*
+ * HDMI 1.3a table 5-14 states that the largest InfoFrame_length is 27,
+ * not including the packet header or checksum byte. We include the
+ * checksum byte in HDMI_INFOFRAME_HEADER_SIZE, so this should allow
+ * HDMI_INFOFRAME_SIZE(MAX) to be the largest buffer we could ever need
+ * for any HDMI infoframe.
+ */
+#define HDMI_MAX_INFOFRAME_SIZE    27
+
 #define HDMI_INFOFRAME_SIZE(type)	\
 	(HDMI_INFOFRAME_HEADER_SIZE + HDMI_ ## type ## _INFOFRAME_SIZE)
 
-- 
2.45.2