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

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Date:   Tue, 18 Jul 2017 08:16:07 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Chris Zhong <zyw@...k-chips.com>
Cc:     Sean Paul <seanpaul@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Mark yao <mark.yao@...k-chips.com>,
        Heiko Stübner <heiko@...ech.de>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Shashank Sharma <shashank.sharma@...el.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Thierry Reding <treding@...dia.com>,
        linux-fbdev@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] video/hdmi: Introduce helpers for the HDMI audio
 infoframe payload

Hi,

On Tue, Jul 18, 2017 at 4:20 AM, Chris Zhong <zyw@...k-chips.com> 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@...k-chips.com>
> ---
>
> 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.


> +               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?


> @@ -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
>