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

[Chris Zhong]

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 <zyw@xxxxxxxxxxxxxx> wrote:
> > 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 <zyw@xxxxxxxxxxxxxx>
> > ---
> >
> > 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)"

> > +               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.


> > @@ -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.
>
> > -
> > -       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).
>
> >   enum hdmi_3d_structure {
> >          HDMI_3D_STRUCTURE_INVALID = -1,
> >          HDMI_3D_STRUCTURE_FRAME_PACKING = 0,
> > --
> > 2.7.4

--
Chris Zhong