linux-kernel - Re: [PATCH v3 1/1] drm: sun4i: hdmi: Add support for sun4i HDMI encoder audio

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Date:   Mon, 3 Feb 2020 13:23:27 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Stefan Mavrodiev <stefan@...mex.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVERS FOR ALLWINNER A10" 
        <dri-devel@...ts.freedesktop.org>,
        "moderated list:ARM/Allwinner sunXi SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v3 1/1] drm: sun4i: hdmi: Add support for sun4i HDMI
 encoder audio

Hi,

On Thu, Jan 30, 2020 at 08:20:55AM +0200, Stefan Mavrodiev wrote:
> On 1/29/20 6:43 PM, Maxime Ripard wrote:
> > On Tue, Jan 28, 2020 at 04:06:42PM +0200, Stefan Mavrodiev wrote:
> > > diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> > > index 68d4644ac2dc..4cd35c97c503 100644
> > > --- a/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> > > +++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_enc.c
> > > @@ -23,6 +23,8 @@
> > >   #include <drm/drm_print.h>
> > >   #include <drm/drm_probe_helper.h>
> > >
> > > +#include <sound/soc.h>
> > > +
> > >   #include "sun4i_backend.h"
> > >   #include "sun4i_crtc.h"
> > >   #include "sun4i_drv.h"
> > > @@ -87,6 +89,10 @@ static void sun4i_hdmi_disable(struct drm_encoder *encoder)
> > >
> > >   	DRM_DEBUG_DRIVER("Disabling the HDMI Output\n");
> > >
> > > +#ifdef CONFIG_DRM_SUN4I_HDMI_AUDIO
> > > +	sun4i_hdmi_audio_destroy(hdmi);
> > > +#endif
> > > +
> > >   	val = readl(hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
> > >   	val &= ~SUN4I_HDMI_VID_CTRL_ENABLE;
> > >   	writel(val, hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
> > > @@ -114,6 +120,11 @@ static void sun4i_hdmi_enable(struct drm_encoder *encoder)
> > >   		val |= SUN4I_HDMI_VID_CTRL_HDMI_MODE;
> > >
> > >   	writel(val, hdmi->base + SUN4I_HDMI_VID_CTRL_REG);
> > > +
> > > +#ifdef CONFIG_DRM_SUN4I_HDMI_AUDIO
> > > +	if (hdmi->hdmi_audio && sun4i_hdmi_audio_create(hdmi))
> > > +		DRM_ERROR("Couldn't create the HDMI audio adapter\n");
> > > +#endif
> > I really don't think we should be creating / removing the audio card
> > at enable / disable time.
>
> For me it's unnatural to have sound card all the time, even when the HDMI
> is not plugged-in.

It's also a matter of being consistent: pretty much everyone else is
doing it:
  * vc4 (RaspberryPi)
    https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/vc4/vc4_hdmi.c#L1437

  * omap
    https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/omapdrm/dss/hdmi4.c#L620

  * sti
    https://elixir.bootlin.com/linux/v5.5.1/source/drivers/gpu/drm/sti/sti_hdmi.c#L1310

  * msm
    https://elixir.bootlin.com/linux/v5.5.1/source/drivers/gpu/drm/msm/hdmi/hdmi.c#L597

etc...

If we were to think about this at a more theorical level though, it's
pretty much the same case than having a sound card but no headphone
attached, or having a display engine but no display attached. In both
case, you register the driver before having a sink, you just let the
userspace know that there's nothing connected on the other end.

Maxime

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