Message-ID:
 <PAXPR04MB9448EF507CB5C18A43239A80F49E2@PAXPR04MB9448.eurprd04.prod.outlook.com>
Date: Fri, 6 Sep 2024 02:50:08 +0000
From: Sandor Yu <sandor.yu@....com>
To: Maxime Ripard <mripard@...nel.org>
CC: "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
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	<linux-phy@...ts.infradead.org>, "kernel@...gutronix.de"
	<kernel@...gutronix.de>, dl-linux-imx <linux-imx@....com>, Oliver Brown
	<oliver.brown@....com>, "alexander.stein@...tq-group.com"
	<alexander.stein@...tq-group.com>, "sam@...nborg.org" <sam@...nborg.org>
Subject: RE: [EXT] Re: [PATCH v16 4/8] drm: bridge: Cadence: Add MHDP8501
 DP/HDMI driver



> 
> On Tue, Sep 03, 2024 at 06:07:25AM GMT, Sandor Yu wrote:
> > Hi Maxime,
> >
> > Thanks for your comments,
> >
> > > -----Original Message-----
> > > From: dri-devel <dri-devel-bounces@...ts.freedesktop.org> On Behalf
> > > Of Maxime Ripard
> > > Sent: 2024年7月2日 21:25
> > > To: Sandor Yu <sandor.yu@....com>
> > > Cc: dmitry.baryshkov@...aro.org; andrzej.hajda@...el.com;
> > > neil.armstrong@...aro.org; Laurent Pinchart
> > > <laurent.pinchart@...asonboard.com>; jonas@...boo.se;
> > > jernej.skrabec@...il.com; airlied@...il.com; daniel@...ll.ch;
> > > robh+dt@...nel.org; krzysztof.kozlowski+dt@...aro.org;
> > > shawnguo@...nel.org; s.hauer@...gutronix.de; festevam@...il.com;
> > > vkoul@...nel.org; dri-devel@...ts.freedesktop.org;
> > > devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> > > linux-kernel@...r.kernel.org; linux-phy@...ts.infradead.org;
> > > kernel@...gutronix.de; dl-linux-imx <linux-imx@....com>; Oliver
> > > Brown <oliver.brown@....com>; alexander.stein@...tq-group.com;
> > > sam@...nborg.org
> > > Subject: [EXT] Re: [PATCH v16 4/8] drm: bridge: Cadence: Add
> > > MHDP8501 DP/HDMI driver
> > >
> > > Hi,
> > >
> > > There's still the scrambler issue we discussed on v15, but I have
> > > some more comments.
> > >
> > > On Tue, Jul 02, 2024 at 08:22:36PM GMT, Sandor Yu wrote:
> > > > +enum drm_connector_status cdns_mhdp8501_detect(struct
> > > > +cdns_mhdp8501_device *mhdp) {
> > > > +	u8 hpd = 0xf;
> > > > +
> > > > +	hpd = cdns_mhdp8501_read_hpd(mhdp);
> > > > +	if (hpd == 1)
> > > > +		return connector_status_connected;
> > > > +	else if (hpd == 0)
> > > > +		return connector_status_disconnected;
> > > > +
> > > > +	dev_warn(mhdp->dev, "Unknown cable status, hdp=%u\n", hpd);
> > > > +	return connector_status_unknown; }
> > > > +
> > > > +static void hotplug_work_func(struct work_struct *work) {
> > > > +	struct cdns_mhdp8501_device *mhdp = container_of(work,
> > > > +						     struct cdns_mhdp8501_device,
> > > > +						     hotplug_work.work);
> > > > +	enum drm_connector_status status =
> cdns_mhdp8501_detect(mhdp);
> > > > +
> > > > +	drm_bridge_hpd_notify(&mhdp->bridge, status);
> > > > +
> > > > +	if (status == connector_status_connected) {
> > > > +		/* Cable connected  */
> > > > +		DRM_INFO("HDMI/DP Cable Plug In\n");
> > > > +		enable_irq(mhdp->irq[IRQ_OUT]);
> > > > +	} else if (status == connector_status_disconnected) {
> > > > +		/* Cable Disconnected  */
> > > > +		DRM_INFO("HDMI/DP Cable Plug Out\n");
> > > > +		enable_irq(mhdp->irq[IRQ_IN]);
> > > > +	}
> > > > +}
> > >
> > > You shouldn't play with the interrupt being enabled here: hotplug
> > > interrupts should always enabled.
> > >
> > > If you can't for some reason, the reason should be documented in your
> driver.
> >
> > iMX8MQ have two HPD interrupters, one for plugout and the other for
> > plugin, because they could not be masked, so we have to enable one and
> disable the other.
> > I will add more comments here.
> 
> Right, but why do you need to enable and disable them? Do you get spurious
> interrupts?

They don't have status registers and cannot be masked. If they are not disabled, 
they will continuously generate interrupts. Therefore, I have to disable one and enable the other.

> 
> > >
> > > > +	/* Mailbox protect for HDMI PHY access */
> > > > +	mutex_lock(&mhdp->mbox_mutex);
> > > > +	ret = phy_init(mhdp->phy);
> > > > +	mutex_unlock(&mhdp->mbox_mutex);
> > > > +	if (ret) {
> > > > +		dev_err(dev, "Failed to initialize PHY: %d\n", ret);
> > > > +		goto clk_disable;
> > > > +	}
> > > > +
> > > > +	/* Mailbox protect for HDMI PHY access */
> > > > +	mutex_lock(&mhdp->mbox_mutex);
> > > > +	ret = phy_set_mode(mhdp->phy, phy_mode);
> > > > +	mutex_unlock(&mhdp->mbox_mutex);
> > > > +	if (ret) {
> > > > +		dev_err(dev, "Failed to configure PHY: %d\n", ret);
> > > > +		goto clk_disable;
> > > > +	}
> > >
> > > Why do you need a shared mutex between the phy and HDMI controller?
> >
> > Both PHY and HDMI controller could access to the HDMI firmware by
> > mailbox, So add mutex to avoid race condition.
> 
> That should be handled at either the phy or mailbox level, not in your hdmi
> driver.
> 
In both HDMI driver and PHY driver, every mailbox access had protected by its owns mutex. 
However, this mutex can only protect each mailbox access within their respective drivers, 
and it cannot provide protection for access between the HDMI and PHY drivers.

The PHY driver only provides two API functions, and these functions are only called in the HDMI driver. 
Therefore, when accessing these functions, we use a mutex to protect them. 
This ensures that mailbox access is protected across different PHY and HDMI drivers.

> > >
> > > > +static enum drm_mode_status
> > > > +cdns_hdmi_tmds_char_rate_valid(const struct drm_bridge *bridge,
> > > > +			       const struct drm_display_mode *mode,
> > > > +			       unsigned long long tmds_rate) {
> > > > +	struct cdns_mhdp8501_device *mhdp = bridge->driver_private;
> > > > +	union phy_configure_opts phy_cfg;
> > > > +	int ret;
> > > > +
> > > > +	phy_cfg.hdmi.tmds_char_rate = tmds_rate;
> > > > +
> > > > +	/* Mailbox protect for HDMI PHY access */
> > > > +	mutex_lock(&mhdp->mbox_mutex);
> > > > +	ret = phy_validate(mhdp->phy, PHY_MODE_HDMI, 0, &phy_cfg);
> > > > +	mutex_unlock(&mhdp->mbox_mutex);
> > > > +	if (ret < 0)
> > > > +		return MODE_CLOCK_RANGE;
> > > > +
> > > > +	return MODE_OK;
> > > > +}
> > > > +
> > > > +static enum drm_mode_status
> > > > +cdns_hdmi_bridge_mode_valid(struct drm_bridge *bridge,
> > > > +			    const struct drm_display_info *info,
> > > > +			    const struct drm_display_mode *mode) {
> > > > +	unsigned long long tmds_rate;
> > > > +
> > > > +	/* We don't support double-clocked and Interlaced modes */
> > > > +	if (mode->flags & DRM_MODE_FLAG_DBLCLK ||
> > > > +	    mode->flags & DRM_MODE_FLAG_INTERLACE)
> > > > +		return MODE_BAD;
> > > > +
> > > > +	/* MAX support pixel clock rate 594MHz */
> > > > +	if (mode->clock > 594000)
> > > > +		return MODE_CLOCK_HIGH;
> > >
> > > This needs to be in the tmds_char_rate_valid function
> > This clock rate check is covered by function tmds_char_rate_valid() It
> > could be removed if keep function tmds_char_rate_valid() be called by
> mode_valid.
> 
> Yeah, it's not something you should have to duplicate.
> 
> > >
> > > > +	if (mode->hdisplay > 3840)
> > > > +		return MODE_BAD_HVALUE;
> > > > +
> > > > +	if (mode->vdisplay > 2160)
> > > > +		return MODE_BAD_VVALUE;
> > > > +
> > > > +	tmds_rate = mode->clock * 1000ULL;
> > > > +	return cdns_hdmi_tmds_char_rate_valid(bridge, mode, tmds_rate);
> > >
> > > It will already be called by the core so this is redundant.
> >
> > mode_valid function is use to filter the mode list in
> > drm_helper_probe_single_connector_modes(),
> > if function cdns_hdmi_tmds_char_rate_valid() is not called, unsupported
> modes will in mode list.
> 
> It's probably something we should deal with in the core somehow. I'm not
> entirely sure how to reconcile drm_bridge_connector and the hdmi
> framework there, but we should at the very least provide a mode_valid
> helper for bridges.
> 
I agree with that. In fact, I'm a bit confused about the current mode_valid and tmds_char_rate_valid functions.
Ideally, we should find a way to make tmds_char_rate_valid also work for filtering out the mode list, rather than just during atomic_check.

> > >
> > > > +static void cdns_hdmi_bridge_atomic_enable(struct drm_bridge
> *bridge,
> > > > +					   struct drm_bridge_state *old_state) {
> > > > +	struct cdns_mhdp8501_device *mhdp = bridge->driver_private;
> > > > +	struct drm_atomic_state *state = old_state->base.state;
> > > > +	struct drm_connector *connector;
> > > > +	struct video_info *video = &mhdp->video_info;
> > > > +	struct drm_crtc_state *crtc_state;
> > > > +	struct drm_connector_state *conn_state;
> > > > +	struct drm_display_mode *mode = &mhdp->mode;
> > > > +	union phy_configure_opts phy_cfg;
> > > > +	int ret;
> > > > +
> > > > +	connector = drm_atomic_get_new_connector_for_encoder(state,
> > > > +							     bridge->encoder);
> > > > +	if (WARN_ON(!connector))
> > > > +		return;
> > > > +
> > > > +	mhdp->curr_conn = connector;
> > > > +
> > > > +	conn_state = drm_atomic_get_new_connector_state(state,
> connector);
> > > > +	if (WARN_ON(!conn_state))
> > > > +		return;
> > > > +
> > > > +	crtc_state = drm_atomic_get_new_crtc_state(state,
> conn_state->crtc);
> > > > +	if (WARN_ON(!crtc_state))
> > > > +		return;
> > > > +
> > > > +	video->color_fmt = conn_state->hdmi.output_format;
> > > > +	video->bpc = conn_state->hdmi.output_bpc;
> > > > +
> > > > +	drm_mode_copy(&mhdp->mode, &crtc_state->adjusted_mode);
> > >
> > > Why do you need a copy of all these fields? You should pass the
> > > connector / bridge state around and not copy these fields.
> > >
> > OK, mode will be removed, and it will replace by drm_connector_state.
> >
> > > > +	/* video mode check */
> > > > +	if (mode->clock == 0 || mode->hdisplay == 0 || mode->vdisplay ==
> 0)
> > > > +		return;
> > >
> > > This should be checked in atomic_check, but I'm pretty sure it's
> redundant.
> > OK, It will be removed.
> > >
> > > > +	dev_dbg(mhdp->dev, "Mode: %dx%dp%d\n",
> > > > +		mode->hdisplay, mode->vdisplay, mode->clock);
> > > > +
> > > > +
> 	drm_atomic_helper_connector_hdmi_update_infoframes(connector,
> > > > +state);
> > > > +
> > > > +	/* Line swapping */
> > > > +	cdns_mhdp_reg_write(&mhdp->base, LANES_CONFIG, 0x00400000
> |
> > > > +mhdp->lane_mapping);
> > > > +
> > > > +	mhdp->hdmi.char_rate = drm_hdmi_compute_mode_clock(mode,
> > > > +							   mhdp->video_info.bpc,
> > > > +							   mhdp->video_info.color_fmt);
> > >
> > > The TMDS char rate is already available in the connector_state so
> > > there no need to recompute it.
> > >
> > > > +	phy_cfg.hdmi.tmds_char_rate = mhdp->hdmi.char_rate;
> > >
> > > And you shouldn't store a copy either.
> > OK, variable char_rate will be removed and will use the
> > drm_connector_state-> hdmi.tmds_char_rate
> >
> > >
> > > > +	/* Mailbox protect for HDMI PHY access */
> > > > +	mutex_lock(&mhdp->mbox_mutex);
> > > > +	ret = phy_configure(mhdp->phy, &phy_cfg);
> > > > +	mutex_unlock(&mhdp->mbox_mutex);
> > > > +	if (ret) {
> > > > +		dev_err(mhdp->dev, "%s: phy_configure() failed: %d\n",
> > > > +			__func__, ret);
> > > > +		return;
> > > > +	}
> > > > +
> > > > +	cdns_hdmi_sink_config(mhdp);
> > > > +
> > > > +	ret = cdns_hdmi_ctrl_init(mhdp);
> > > > +	if (ret < 0) {
> > > > +		dev_err(mhdp->dev, "%s, ret = %d\n", __func__, ret);
> > > > +		return;
> > > > +	}
> > > > +
> > > > +	/* Config GCP */
> > > > +	if (mhdp->video_info.bpc == 8)
> > > > +		cdns_hdmi_disable_gcp(mhdp);
> > > > +	else
> > > > +		cdns_hdmi_enable_gcp(mhdp);
> > > > +
> > > > +	ret = cdns_hdmi_mode_config(mhdp, mode, &mhdp->video_info);
> > > > +	if (ret < 0) {
> > > > +		dev_err(mhdp->dev, "CDN_API_HDMITX_SetVic_blocking ret
> > > = %d\n", ret);
> > > > +		return;
> > > > +	}
> > > > +}
> > > > +
> > > > +static int cdns_hdmi_bridge_clear_infoframe(struct drm_bridge
> *bridge,
> > > > +					    enum hdmi_infoframe_type type) {
> > > > +	return 0;
> > > > +}
> > >
> > > Either implement it or don't, but an empty function is dead code.
> > Must have function hdmi_clear_infoframe when set
> DRM_BRIDGE_OP_HDMI
> > flag in &drm_bridge->ops, otherwise the drm_bridge_connector_init() will
> fail.
> > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tr
> > ee/drivers/gpu/drm/drm_bridge_connector.c?h=next-20240902#n419
> 
> That's a strong hint that you should implement it, not workaround it :)

OK, I will add it.

Sandor

> 
> Maxime

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