Re: [PATCH v4 4/4] drm/i915: set proper N/CTS in modeset

[Jani Nikula <jani.nikula@linux.intel.com>]

On Wed, 12 Aug 2015, "Yang, Libin" <libin.yang@intel.com> wrote:
> Hi Jani,
>
>> -----Original Message-----
>> From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
>> Sent: Tuesday, August 11, 2015 4:14 PM
>> To: Yang, Libin; alsa-devel@alsa-project.org; tiwai@suse.de; intel-
>> gfx@lists.freedesktop.org; daniel.vetter@ffwll.ch
>> Subject: RE: [Intel-gfx] [PATCH v4 4/4] drm/i915: set proper N/CTS in
>> modeset
>> 
>> On Tue, 11 Aug 2015, "Yang, Libin" <libin.yang@intel.com> wrote:
>> > Hi Jani,
>> >
>> >> -----Original Message-----
>> >> From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
>> >> Sent: Tuesday, August 11, 2015 3:14 PM
>> >> To: Yang, Libin; alsa-devel@alsa-project.org; tiwai@suse.de; intel-
>> >> gfx@lists.freedesktop.org; daniel.vetter@ffwll.ch
>> >> Subject: RE: [Intel-gfx] [PATCH v4 4/4] drm/i915: set proper N/CTS in
>> >> modeset
>> >>
>> >> On Tue, 11 Aug 2015, "Yang, Libin" <libin.yang@intel.com> wrote:
>> >> > Hi Jani,
>> >> >
>> >> > Thanks for careful reviewing for all the patches, please
>> >> > see my comments.
>> >> >
>> >> >> -----Original Message-----
>> >> >> From: Jani Nikula [mailto:jani.nikula@linux.intel.com]
>> >> >> Sent: Monday, August 10, 2015 8:10 PM
>> >> >> To: Yang, Libin; alsa-devel@alsa-project.org; tiwai@suse.de; intel-
>> >> >> gfx@lists.freedesktop.org; daniel.vetter@ffwll.ch
>> >> >> Subject: Re: [Intel-gfx] [PATCH v4 4/4] drm/i915: set proper N/CTS
>> in
>> >> >> modeset
>> >> >>
>> >> >> On Mon, 10 Aug 2015, libin.yang@intel.com wrote:
>> >> >> > From: Libin Yang <libin.yang@intel.com>
>> >> >> >
>> >> >> > When modeset occurs and the TMDS frequency is set to some
>> >> >> > speical value, the N/CTS need to be set manually if audio
>> >> >> > is playing.
>> >> >>
>> >> >> When modeset occurs, we disable everything, and then re-enable
>> >> >> everything, and notify the audio driver every step of the way. IIUC
>> >> >> there should be no audio playing across the modeset, and when
>> the
>> >> >> modeset is complete and we've set the valid ELD, the audio driver
>> >> >> should
>> >> >> call the callback from the earlier patches to set the correct audio
>> >> >> rate.
>> >> >>
>> >> >> Why is this patch needed? Please enlighten me.
>> >> >
>> >> > Please image this scenario: when audio is playing, the gfx driver
>> >> > does the modeset. In this situation, after modeset, audio driver
>> >> > will do nothing and continue playing. And audio driver will not call
>> >> > set_ncts.
>> >>
>> >> Why does the audio driver not do anything here? Whenever there's
>> a
>> >> modeset, the graphics driver will disable audio and invalidate the
>> ELD,
>> >> which should cause an interrupt to notify the audio driver about
>> >> this. This is no different from a hot-unplug, in fact I can't see how
>> >> the audio driver could even detect whether there's been a hotplug
>> or
>> >> not
>> >> when there's a codec disable/enable.
>> >
>> > Yes, it will trigger an interrupt to audio driver when unplug
>> > and another interrupt for hotplug. But from audio driver,
>> > we will not stop the playing and resume the playing based
>> > on the hotplug or modeset. The audio is always playing during
>> > the hotplug/modeset.
>> 
>> But the whole display, and consequently ELD, might have changed
>> during
>> the hotplug, why do you assume you can just keep playing?! The
>> display
>> might even have changed from HDMI to DP or vice versa.
>
> The eld info changing will not impact the audio playing.
> Actually, you can image the monitor as a digital speaker, just
> like the headphone to the analog audio. Unplug the speaker
> will not impact on the audio playing. Of course , there is a
> little difference, when monitor hotplug, in the interrupt,
> we may change the codec configuration dynamically. 
>
> And audio driver supply the mechanism to stop the
> audio playing when hotplug if the HW requires.
>
>> 
>> We've also been putting a lot of effort into not depending on previous
>> state when enabling the outputs, for more reliability. We generally
>> don't do partial changes, we disable everything and then enable
>> again. And now you're suggesting we look at some register which for all
>> we know may have been valid for some other display?
>
> In the patch, it will not depend on previous state, I think. We
> read the register value which is based on the state after modeset.

Okay, let's have the patches cleaned up and see. It'll be easier and
quicker to solicit more review on that than this expanding thread.

Please find one more code comment below.

>
>> 
>> Timeout.
>> 
>> 
>> BR,
>> Jani.
>> 
>> 
>> >
>> >>
>> >> BR,
>> >> Jani.
>> >>
>> >>
>> >> >
>> >> >>
>> >> >> Also some comments in-line, provided you've convinced me first. ;)
>> >> >>
>> >> >> > Signed-off-by: Libin Yang <libin.yang@intel.com>
>> >> >> > ---
>> >> >> >  drivers/gpu/drm/i915/i915_reg.h    |  6 ++++++
>> >> >> >  drivers/gpu/drm/i915/intel_audio.c | 42
>> >> >> ++++++++++++++++++++++++++++++++++++++
>> >> >> >  2 files changed, 48 insertions(+)
>> >> >> >
>> >> >> > diff --git a/drivers/gpu/drm/i915/i915_reg.h
>> >> >> b/drivers/gpu/drm/i915/i915_reg.h
>> >> >> > index da2d128..85f3beb 100644
>> >> >> > --- a/drivers/gpu/drm/i915/i915_reg.h
>> >> >> > +++ b/drivers/gpu/drm/i915/i915_reg.h
>> >> >> > @@ -7030,6 +7030,12 @@ enum skl_disp_power_wells {
>> >> >> >
>> 	_HSW_AUD_DIG_CNVT_2)
>> >> >> >  #define DIP_PORT_SEL_MASK		0x3
>> >> >> >
>> >> >> > +#define _HSW_AUD_STR_DESC_1		0x65084
>> >> >> > +#define _HSW_AUD_STR_DESC_2		0x65184
>> >> >> > +#define AUD_STR_DESC(pipe)	_PIPE(pipe, \
>> >> >> > +
>> _HSW_AUD_STR_DESC_1,
>> >> >> 	\
>> >> >> > +
>> _HSW_AUD_STR_DESC_2)
>> >> >> > +
>> >> >> >  #define _HSW_AUD_EDID_DATA_A		0x65050
>> >> >> >  #define _HSW_AUD_EDID_DATA_B		0x65150
>> >> >> >  #define HSW_AUD_EDID_DATA(pipe) _PIPE(pipe, \
>> >> >> > diff --git a/drivers/gpu/drm/i915/intel_audio.c
>> >> >> b/drivers/gpu/drm/i915/intel_audio.c
>> >> >> > index eddf37f..082f96d 100644
>> >> >> > --- a/drivers/gpu/drm/i915/intel_audio.c
>> >> >> > +++ b/drivers/gpu/drm/i915/intel_audio.c
>> >> >> > @@ -235,6 +235,9 @@ static void
>> >> hsw_audio_codec_enable(struct
>> >> >> drm_connector *connector,
>> >> >> >  	const uint8_t *eld = connector->eld;
>> >> >> >  	uint32_t tmp;
>> >> >> >  	int len, i;
>> >> >> > +	int cvt_idx;
>> >> >> > +	int n_low, n_up, n;
>> >> >> > +	int base_rate, mul, div, rate;
>> >> >> >
>> >> >> >  	DRM_DEBUG_KMS("Enable audio codec on pipe %c, %u
>> bytes
>> >> >> ELD\n",
>> >> >> >  		      pipe_name(pipe), drm_eld_size(eld));
>> >> >> > @@ -267,6 +270,21 @@ static void
>> >> hsw_audio_codec_enable(struct
>> >> >> drm_connector *connector,
>> >> >> >  	tmp |= AUDIO_ELD_VALID(pipe);
>> >> >> >  	I915_WRITE(HSW_AUD_PIN_ELD_CP_VLD, tmp);
>> >> >> >
>> >> >> > +	if ((mode->clock == 297000) ||
>> >> >> > +		(mode->clock == DIV_ROUND_UP(297000 * 1000,
>> >> >> 1001))) {

Please abstract that condition into a helper and give it a helpful
name. That's repeated many times now, in this and negated forms, and I
want the compiler to ensure it's the same in each place.

Thanks,
Jani.

>> >> >> > +		tmp =
>> I915_READ(HSW_AUD_PIPE_CONN_SEL_CTRL);
>> >> >> > +		cvt_idx = (tmp >> pipe*8) & 0xff;
>> >> >> > +		tmp = I915_READ(AUD_STR_DESC(cvt_idx));
>> >> >> > +		base_rate = tmp & (1 << 14);
>> >> >> > +		if (base_rate == 0)
>> >> >> > +			rate = 48000;
>> >> >> > +		else
>> >> >> > +			rate = 44100;
>> >> >> > +		mul = (tmp & (0x7 << 11)) + 1;
>> >> >> > +		div = (tmp & (0x7 << 8)) + 1;
>> >> >> > +		rate = rate * mul / div;
>> >> >> > +	}
>> >> >>
>> >> >> This should be abstracted to a separate function.
>> >> >
>> >> > Yes. I will do it.
>> >> >
>> >> >>
>> >> >> > +
>> >> >> >  	/* Enable timestamps */
>> >> >> >  	tmp = I915_READ(HSW_AUD_CFG(pipe));
>> >> >> >  	tmp &= ~AUD_CONFIG_N_VALUE_INDEX;
>> >> >> > @@ -276,6 +294,30 @@ static void
>> >> hsw_audio_codec_enable(struct
>> >> >> drm_connector *connector,
>> >> >> >  		tmp |= AUD_CONFIG_N_VALUE_INDEX;
>> >> >> >  	else
>> >> >> >  		tmp |= audio_config_hdmi_pixel_clock(mode);
>> >> >> > +
>> >> >> > +	if ((mode->clock != 297000) &&
>> >> >> > +		(mode->clock != DIV_ROUND_UP(297000 * 1000,
>> >> >> 1001))) {
>> >> >> > +		tmp &= ~AUD_CONFIG_N_PROG_ENABLE;
>> >> >> > +	} else {
>> >> >> > +		for (i = 0; i < ARRAY_SIZE(aud_ncts); i++) {
>> >> >> > +			if ((rate == aud_ncts[i].sample_rate) &&
>> >> >> > +				(mode->clock ==
>> aud_ncts[i].clock)) {
>> >> >> > +				n = aud_ncts[i].n;
>> >> >> > +				break;
>> >> >> > +			}
>> >> >> > +		}
>> >> >> > +		if (n != 0) {
>> >> >> > +			tmp |= AUD_CONFIG_N_PROG_ENABLE;
>> >> >> > +			n_low = n & 0xfff;
>> >> >> > +			n_up = (n >> 12) & 0xff;
>> >> >> > +			tmp |= AUD_CONFIG_N_PROG_ENABLE;
>> >> >> > +			tmp &= ~AUD_CONFIG_UPPER_N_MASK;
>> >> >> > +			tmp |= (n_up <<
>> >> >> AUD_CONFIG_UPPER_N_SHIFT);
>> >> >> > +			tmp &=
>> ~AUD_CONFIG_LOWER_N_MASK;
>> >> >> > +			tmp |= (n_low <<
>> >> >> AUD_CONFIG_LOWER_N_SHIFT);
>> >> >> > +		}
>> >> >> > +	}
>> >> >>
>> >> >> Please de-duplicate the copy-paste from patch 2. At the very least
>> >> you
>> >> >> should use a helper for finding the parameters from the table.
>> >> >
>> >> > OK. I see.
>> >> >
>> >> > Regards,
>> >> > Libin
>> >> >
>> >> >>
>> >> >> > +
>> >> >> >  	I915_WRITE(HSW_AUD_CFG(pipe), tmp);
>> >> >> >  }
>> >> >> >
>> >> >> > --
>> >> >> > 1.9.1
>> >> >> >
>> >> >> > _______________________________________________
>> >> >> > Intel-gfx mailing list
>> >> >> > Intel-gfx@lists.freedesktop.org
>> >> >> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>> >> >>
>> >> >> --
>> >> >> Jani Nikula, Intel Open Source Technology Center
>> >>
>> >> --
>> >> Jani Nikula, Intel Open Source Technology Center
>> 
>> --
>> Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center
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