From: Takashi Iwai <tiwai@suse.de>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Fabio Estevam <fabio.estevam@freescale.com>,
alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org,
dri-devel@lists.freedesktop.org, Jaroslav Kysela <perex@perex.cz>,
linux-rockchip@lists.infradead.org,
Mark Brown <broonie@kernel.org>, Yakir Yang <ykk@rock-chips.com>,
Andy Yan <andy.yan@rock-chips.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/9] drm: bridge/dw_hdmi-ahb-audio: add audio driver
Date: Mon, 10 Aug 2015 14:23:07 +0200 [thread overview]
Message-ID: <s5hegjb5o44.wl-tiwai@suse.de> (raw)
In-Reply-To: <20150810103921.GR7557@n2100.arm.linux.org.uk>
On Mon, 10 Aug 2015 12:39:21 +0200,
Russell King - ARM Linux wrote:
>
> On Mon, Aug 10, 2015 at 12:05:07PM +0200, Takashi Iwai wrote:
> > On Sat, 08 Aug 2015 18:10:06 +0200,
> > Russell King wrote:
> > > +static irqreturn_t snd_dw_hdmi_irq(int irq, void *data)
> > > +{
> > > + struct snd_dw_hdmi *dw = data;
> > > + struct snd_pcm_substream *substream;
> > > + unsigned stat;
> > > +
> > > + stat = readb_relaxed(dw->data.base + HDMI_IH_AHBDMAAUD_STAT0);
> > > + if (!stat)
> > > + return IRQ_NONE;
> > > +
> > > + writeb_relaxed(stat, dw->data.base + HDMI_IH_AHBDMAAUD_STAT0);
> > > +
> > > + substream = dw->substream;
> > > + if (stat & HDMI_IH_AHBDMAAUD_STAT0_DONE && substream) {
> > > + snd_pcm_period_elapsed(substream);
> > > + if (dw->substream)
> > > + dw_hdmi_start_dma(dw);
> > > + }
> >
> > Don't we need locking?
>
> Possibly.
>
> > In theory, the trigger can be issued while the irq is being handled.
>
> Well, we can't have a lock around the whole of the above, because that
> results in deadlock (as snd_pcm_period_elapsed() can end up calling into
> the trigger method.)
Yes, and a usual workaround is to unlock temporarily at calling
snd_pcm_period_elapsed(), then relock or call it at the end of
handler.
> I'm not happy to throw a spinlock around this
> because of the in-built format conversion (something else I'm really not
> happy about - which has to exist here because alsalib is soo painful
> to add custom sample reformatting to - such modules have to be built
> as part of alsalib itself rather than an add-on module.)
I admit that alsa-lib code is very horrible to follow -- but I guess
the change you'd need for iec958 plugin would be fairly small. We can
add a config option and let iec958 behaving slightly differently
depending on it.
Meanwhile, having an in-kernel workaround makes it much easier to
deploy, so I think it's OK to have this in driver for now.
> > > +static int dw_hdmi_trigger(struct snd_pcm_substream *substream, int cmd)
> > > +{
> > > + struct snd_dw_hdmi *dw = substream->private_data;
> > > + int ret = 0;
> > > +
> > > + switch (cmd) {
> > > + case SNDRV_PCM_TRIGGER_START:
> > > + dw->buf_offset = 0;
> > > + dw->substream = substream;
> > > + dw_hdmi_start_dma(dw);
> > > + dw_hdmi_audio_enable(dw->data.hdmi);
> > > + substream->runtime->delay = substream->runtime->period_size;
> > > + break;
> > > +
> > > + case SNDRV_PCM_TRIGGER_STOP:
> > > + dw_hdmi_stop_dma(dw);
> > > + dw_hdmi_audio_disable(dw->data.hdmi);
> > > + break;
> > > +
> > > + default:
> > > + ret = -EINVAL;
> > > + break;
> >
> > SNDRV_PCM_TRIGGER_SUSPEND may be passed at suspend, too.
>
> I think rather than adding code which would be difficult for me to test,
> I'd instead remove the suspend/resume callbacks, or at least disable them
> until someone can test that feature, or is willing to implement it.
That's fine.
> > > +static snd_pcm_uframes_t dw_hdmi_pointer(struct snd_pcm_substream *substream)
> > > +{
> > > + struct snd_pcm_runtime *runtime = substream->runtime;
> > > + struct snd_dw_hdmi *dw = substream->private_data;
> > > +
> > > + return bytes_to_frames(runtime, dw->buf_offset);
> >
> > So, this returns the offset that has been reformatted. Does the
> > hardware support any better position reporting? We may give the delay
> > from the driver if possible.
>
> Basically, no. Reading a 32-bit DMA position as separate bytes while
> DMA is active is racy.
>
> This is the best we can do, and the way we report the position has been
> arrived at after what's getting on for two years of testing with
> pulseaudio, vlc direct access & spdif pass-through, aplay, etc:
>
> Author: Russell King <rmk+kernel@arm.linux.org.uk>
> Date: Thu Nov 7 16:01:45 2013 +0000
>
> drm: bridge/dw_hdmi-ahb-audio: add audio driver
OK, then this is a driver with the low update granularity. Hopefully
we'll get some good API to indicate that in near future, as we've been
discussing about it for a while.
thanks,
Takashi
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next prev parent reply other threads:[~2015-08-10 12:23 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-08 16:02 [PATCH 00/12] dw-hdmi development Russell King - ARM Linux
2015-08-08 16:09 ` [PATCH 0/9] dw-hdmi audio support Russell King - ARM Linux
2015-08-08 16:10 ` [PATCH 1/9] drm: bridge/dw_hdmi-ahb-audio: add audio driver Russell King
2015-08-10 10:05 ` Takashi Iwai
2015-08-10 10:39 ` Russell King - ARM Linux
2015-08-10 12:23 ` Takashi Iwai [this message]
2015-08-10 16:49 ` Russell King - ARM Linux
2015-08-10 18:16 ` Mark Brown
2015-08-14 13:54 ` [PATCH v2 1/9] drm: bridge/dw_hdmi-ahb-audio: add audio driver David Airlie <airlied@linux.ie>, Sascha Hauer <s.hauer@pengutronix.de>, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Jaroslav Kysela <perex@perex.cz>, linux-rockchip@lists.infradead.org, Mark Brown <broonie@kernel.org>, Philipp Zabel <p.zabel@pengutronix.de>, Yakir Yang <ykk@rock-chips.com>, Andy Yan <andy.yan@rock-chips.com>, Jon Nettleton <jon.nettleton@gmail.com>, linux-arm-kernel@lists.infradead.org Russell King
2015-08-14 14:04 ` [PATCH v2 1/9] drm: bridge/dw_hdmi-ahb-audio: add audio driver Russell King
2015-08-14 14:34 ` [alsa-devel] " Takashi Iwai
2015-10-06 18:07 ` [PATCH " Fabio Estevam
2015-10-06 18:18 ` Russell King - ARM Linux
2015-10-06 18:45 ` Fabio Estevam
2015-10-06 18:54 ` Russell King - ARM Linux
2015-10-06 20:25 ` Fabio Estevam
2015-10-09 16:00 ` Russell King - ARM Linux
2015-10-09 16:02 ` Fabio Estevam
2015-10-09 16:11 ` Russell King - ARM Linux
2015-08-08 16:10 ` [PATCH 2/9] drm: bridge/dw_hdmi-ahb-audio: parse ELD from HDMI driver Russell King
2015-08-08 16:10 ` [PATCH 3/9] drm: bridge/dw_hdmi-ahb-audio: basic support for multi-channel PCM audio Russell King
2015-08-08 16:10 ` [PATCH 4/9] drm: bridge/dw_hdmi-ahb-audio: allow larger buffer sizes Russell King
2015-08-08 16:10 ` [PATCH 5/9] drm: bridge/dw_hdmi: avoid being recursive in N calculation Russell King
2015-09-04 17:50 ` Doug Anderson
2015-08-08 16:10 ` [PATCH 6/9] drm: bridge/dw_hdmi: adjust pixel clock values " Russell King
2015-09-04 18:21 ` Doug Anderson
2015-09-04 19:48 ` Doug Anderson
2015-09-04 21:24 ` Russell King - ARM Linux
2015-09-04 23:50 ` Doug Anderson
2015-09-05 0:27 ` Russell King - ARM Linux
2015-09-05 2:03 ` Doug Anderson
2015-09-05 8:31 ` Russell King - ARM Linux
2015-09-05 13:46 ` Doug Anderson
2015-09-05 14:01 ` Russell King - ARM Linux
2015-09-05 19:44 ` Doug Anderson
2015-09-05 8:34 ` Russell King - ARM Linux
2015-09-05 13:50 ` Doug Anderson
2015-08-08 16:10 ` [PATCH 7/9] drm: bridge/dw_hdmi: remove ratio support from ACR code Russell King
2015-09-04 18:24 ` Doug Anderson
2015-08-08 16:10 ` [PATCH 8/9] drm: bridge/dw_hdmi: replace CTS calculation for the ACR Russell King
2015-09-04 20:00 ` Doug Anderson
2015-08-08 16:10 ` [PATCH 9/9] drm: bridge/dw_hdmi-i2s-audio: add audio driver Russell King
2015-08-10 15:48 ` Russell King - ARM Linux
2015-08-10 16:26 ` Yakir Yang
2015-08-27 8:42 ` [PATCH 0/9] dw-hdmi audio support Philipp Zabel
2016-01-05 15:40 ` [alsa-devel] " Jean-Michel Hautbois
2016-01-05 15:54 ` Fabio Estevam
2016-01-05 16:04 ` Russell King - ARM Linux
2016-01-07 8:21 ` Jean-Michel Hautbois
2015-08-10 12:21 ` [PATCH 00/12] dw-hdmi development Thierry Reding
2015-08-18 10:37 ` Russell King - ARM Linux
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