Re: [PATCH v2 1/2] video/hdmi: Introduce helpers for the HDMI audio infoframe payload

Hi Doug


On Tuesday, July 18, 2017 11:16 PM, Doug Anderson wrote:

Hi,

On Tue, Jul 18, 2017 at 4:20 AM, Chris Zhong [off-list ref] wrote:

quoted

The DP is using the same audio infoframe payload as hdmi, per DP 1.3
spec, but it has a different header. Provide a new interface here,
it just packs the payload.

Signed-off-by: Chris Zhong <redacted>
---

Changes in v2: None

  drivers/video/hdmi.c | 66 ++++++++++++++++++++++++++++++++++++++--------------
  include/linux/hdmi.h |  3 ++-
  2 files changed, 50 insertions(+), 19 deletions(-)

diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
index 1cf907e..e0b041e 100644
--- a/drivers/video/hdmi.c
+++ b/drivers/video/hdmi.c

@@ -240,6 +240,49 @@ int hdmi_audio_infoframe_init(struct hdmi_audio_infoframe *frame)
  EXPORT_SYMBOL(hdmi_audio_infoframe_init);

  /**
+ * hdmi_audio_infoframe_pack_payload() - write HDMI audio infoframe payload to
+ * binary buffer
+ * @frame: HDMI audio infoframe
+ * @buffer: destination buffer
+ * @size: size of buffer
+ *
+ * Packs the information contained in the @frame structure into a binary
+ * representation that can be written into the corresponding controller
+ * registers.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+ssize_t hdmi_audio_infoframe_pack_payload(struct hdmi_audio_infoframe *frame,
+                                         void *buffer, size_t size)
+{
+       unsigned char channels;
+       u8 *ptr = buffer;
+
+       if (size < frame->length)

You also need to return -ENOSPC if (size < 5).  That's because below
you always write 5 elements into this array.  I'll leave it to someone
with actual DRM experience to say whether they want a #define of some
sort here.  Probably they do since someone made a #define for
"HDMI_INFOFRAME_HEADER_SIZE".

Also: you don't use frame->length anywhere in this function and it
doesn't seem to be related with packing the payload.  Seems like you
shouldn't check it here.

Actually, I think it should be "if (size < HDMI_AUDIO_INFOFRAME_SIZE)"

quoted

+               return -ENOSPC;
+
+       memset(buffer, 0, size);

I don't think the memset belongs here.  It seems like all this
function is doing is setting up ptr[0] through ptr[4] and the memset()
doesn't belong with that, does it?

I think the length of payload is 10 Bytes(DB1~DB10), per audio infoframe 
Format,
but we only use the front 5 Bytes, the back 5 bytes must be 0. If we 
take the 10
bytes as a whole, it make sense.

quoted

@@ -256,22 +299,15 @@ EXPORT_SYMBOL(hdmi_audio_infoframe_init);
  ssize_t hdmi_audio_infoframe_pack(struct hdmi_audio_infoframe *frame,
                                   void *buffer, size_t size)
  {
-       unsigned char channels;
         u8 *ptr = buffer;
         size_t length;
+       int ret;

         length = HDMI_INFOFRAME_HEADER_SIZE + frame->length;

         if (size < length)
                 return -ENOSPC;

-       memset(buffer, 0, size);

It seems like the memset() belongs here, logically.  This function
deals with the whole buffer so it should be clearing it.

quoted

-
-       if (frame->channels >= 2)
-               channels = frame->channels - 1;
-       else
-               channels = 0;
-
         ptr[0] = frame->type;
         ptr[1] = frame->version;
         ptr[2] = frame->length;

@@ -279,16 +315,10 @@ ssize_t hdmi_audio_infoframe_pack(struct hdmi_audio_infoframe *frame,

         /* start infoframe payload */
         ptr += HDMI_INFOFRAME_HEADER_SIZE;
-
-       ptr[0] = ((frame->coding_type & 0xf) << 4) | (channels & 0x7);
-       ptr[1] = ((frame->sample_frequency & 0x7) << 2) |
-                (frame->sample_size & 0x3);
-       ptr[2] = frame->coding_type_ext & 0x1f;
-       ptr[3] = frame->channel_allocation;
-       ptr[4] = (frame->level_shift_value & 0xf) << 3;
-
-       if (frame->downmix_inhibit)
-               ptr[4] |= BIT(7);
+       ret = hdmi_audio_infoframe_pack_payload(frame, ptr,
+                                       size - HDMI_INFOFRAME_HEADER_SIZE);
+       if (ret)
+               return ret;

         hdmi_infoframe_set_checksum(buffer, length);

diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
index d271ff2..d93c709 100644
--- a/include/linux/hdmi.h
+++ b/include/linux/hdmi.h

@@ -272,7 +272,8 @@ struct hdmi_audio_infoframe {
  int hdmi_audio_infoframe_init(struct hdmi_audio_infoframe *frame);
  ssize_t hdmi_audio_infoframe_pack(struct hdmi_audio_infoframe *frame,
                                   void *buffer, size_t size);
-
+ssize_t hdmi_audio_infoframe_pack_payload(struct hdmi_audio_infoframe *frame,
+                                         void *buffer, size_t size);

nit: seems like you're changing whitespace here (there used to be a
blank line before the enum).

quoted

  enum hdmi_3d_structure {
         HDMI_3D_STRUCTURE_INVALID = -1,
         HDMI_3D_STRUCTURE_FRAME_PACKING = 0,
--
2.7.4

-- 
Chris Zhong