linux-kernel - Re: [PATCH 3/4] drm/vc4: use new helper to get ACR values

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Message-ID: <wass63nz24l4h3umszsyptb5bnkny4h2wmnbeunjrdfhyacl4l@w6emq2ipt552>
Date: Tue, 11 Mar 2025 18:28:50 +0200
From: Dmitry Baryshkov <lumag@...nel.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, Dave Stevenson <dave.stevenson@...pberrypi.com>, 
	Maíra Canal <mcanal@...lia.com>, Raspberry Pi Kernel Maintenance <kernel-list@...pberrypi.com>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 3/4] drm/vc4: use new helper to get ACR values

On Tue, Mar 11, 2025 at 09:07:10AM +0100, Maxime Ripard wrote:
> On Mon, Mar 10, 2025 at 10:18:04PM +0200, Dmitry Baryshkov wrote:
> > On Mon, Mar 10, 2025 at 03:51:53PM +0100, Maxime Ripard wrote:
> > > On Sun, Mar 09, 2025 at 10:13:58AM +0200, Dmitry Baryshkov wrote:
> > > > From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > > > 
> > > > Use drm_hdmi_acr_get_n_cts() helper instead of calculating N and CTS
> > > > values in the VC4 driver.
> > > > 
> > > > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > > > ---
> > > >  drivers/gpu/drm/vc4/vc4_hdmi.c | 10 +++-------
> > > >  drivers/gpu/drm/vc4/vc4_hdmi.h |  7 +++++++
> > > >  2 files changed, 10 insertions(+), 7 deletions(-)
> > > > 
> > 
> > > > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.h b/drivers/gpu/drm/vc4/vc4_hdmi.h
> > > > index e3d989ca302b72533c374dfa3fd0d5bd7fe64a82..0a775dbfe99d45521f3d0a2016555aefa81d7934 100644
> > > > --- a/drivers/gpu/drm/vc4/vc4_hdmi.h
> > > > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.h
> > > > @@ -211,6 +211,13 @@ struct vc4_hdmi {
> > > >  	 * KMS hooks. Protected by @mutex.
> > > >  	 */
> > > >  	enum hdmi_colorspace output_format;
> > > > +
> > > > +	/**
> > > > +	 * @tmds_char_rate: Copy of
> > > > +	 * @drm_connector_state.hdmi.tmds_char_rate for use outside of
> > > > +	 * KMS hooks. Protected by @mutex.
> > > > +	 */
> > > > +	unsigned long long tmds_char_rate;
> > > >  };
> > > 
> > > This should be in drm_connector_hdmi if it's useful
> > 
> > That would mean bringing the state to a non-state structure on the
> > framework level. Is it fine from your POV?
> 
> Sorry, I'm changing my mind a little bit, but it's pretty much the same
> case than for accessing the infoframes from debugfs: we want to get some
> information stored in the state from outside of KMS.
> 
> What we did for the infoframes is that we're actually just taking the
> connection_mutex from the DRM device and access the drm_connector->state
> pointer.
> 
> I guess it would also work for ALSA?

I'd really prefer to follow the drm_connector.infoframes.audio. It makes
sense to group all ALSA-related functionality together. Maybe I should
refactor it to:

struct drm_connector {
    struct {
	struct mutex lock;
	struct drm_connector_hdmi_infoframe audio_infoframe;
	unsigned long long tmds_char_rate;
    } audio;
};

WDYT? If that doesn't sound appealing, I'll go the connetion_mutex and
drm_connector_state way.

-- 
With best wishes
Dmitry