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

Daniel Vetter
2015-08-12T13:10:56Z

On Wed, Aug 12, 2015 at 09:20:17AM +0300, Jani Nikula wrote:
> 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.

It sounds like we actually need to ping the audio side _before_ we do the
hw modeset while computing the pipe_config. That would probably take care
of my rwm concerns, give this thing proper structure and also make sure
N/CTS never get out of sync. Also then we can track this stuff in the
pipe_config and throw the state checker at it to make sure it's all fine.
-Daniel

>
> 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

--
Daniel Vetter
Software Engineer, Intel Corporation