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

From: Maxime Ripard <maxime@cerno.tech>
To: Stefan Mavrodiev <stefan@olimex.com>
Cc: Chen-Yu Tsai <wens@csie.org>, David Airlie <airlied@linux.ie>,
	Daniel Vetter <daniel@ffwll.ch>,
	open list <linux-kernel@vger.kernel.org>,
	"open list:DRM DRIVERS FOR ALLWINNER A10" 
	<dri-devel@lists.freedesktop.org>,
	"moderated list:ARM/Allwinner sunXi SoC support" 
	<linux-arm-kernel@lists.infradead.org>,
	linux-sunxi@googlegroups.com
Subject: Re: [PATCH v3 1/1] drm: sun4i: hdmi: Add support for sun4i HDMI encoder audio
Date: Mon, 3 Feb 2020 13:23:27 +0100	[thread overview]
Message-ID: <20200203122327.fviddfbkfn2bgycn@gilmour.lan> (raw)
In-Reply-To: <64676a4b-e149-146c-81b4-7fd5e792efc5@olimex.com>

[-- Attachment #1: Type: text/plain, Size: 2535 bytes --]

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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 228 bytes --]