Re: [PATCH v3] drm/connector: hdmi: Fix writing Dynamic Range Mastering infoframes

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 27 Aug 2024, Maxime Ripard <mripard@kernel.org> wrote:
> Hi,
>
> On Mon, Aug 26, 2024 at 07:10:11AM GMT, Derek Foreman wrote:
>> 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 the same size as the DRM infoframe.
>> 
>> 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                            | 3 +++
>>  3 files changed, 5 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..3a442a59919e 100644
>> --- a/include/linux/hdmi.h
>> +++ b/include/linux/hdmi.h
>> @@ -59,6 +59,9 @@ enum hdmi_infoframe_type {
>>  #define HDMI_DRM_INFOFRAME_SIZE    26
>>  #define HDMI_VENDOR_INFOFRAME_SIZE  4
>>  
>> +/* The biggest infoframe size */
>> +#define HDMI_MAX_INFOFRAME_SIZE		HDMI_DRM_INFOFRAME_SIZE
>
> Thanks for that patch, it was definitely an oversight on my part. The
> spec defines the max size of an infoframe to be 30 bytes, so we should
> probably use that here?

Defining it like this allows the use of HDMI_INFOFRAME_SIZE(MAX) which
adds the header size. Having some macros include the header size and
some others not would be confusing, I think.

Or then the whole thing needs to be renamed.

BR,
Jani.

>
> Maxime

-- 
Jani Nikula, Intel