Re: [PATCH v3 01/21] drm/vc4: Declare the DSI encoder as a bridge element

[Boris Brezillon <boris.brezillon@collabora.com>]

On Sun, 24 Nov 2019 12:01:30 +0200
Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote:

> Hi Boris,
> 
> Thank you for the patch.
> 
> On Wed, Oct 23, 2019 at 05:44:52PM +0200, Boris Brezillon wrote:
> > Encoder drivers will progressively transition to the drm_bridge
> > interface in place of the drm_encoder one.
> > 
> > Let's start with the VC4 driver, and use the ->pre_{enable,disable}()
> > hooks to get rid of the hack resetting encoder->bridge.next (which was
> > needed to control the encoder/bridge enable/disable sequence).
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
> > ---
> > Changes in v3:
> > * Embed a drm_bridge object in vc4_dsi since drm_encoder no longer has
> >   a dummy bridge
> > 
> > Changes in v2:
> > * New patch (replaces "drm/vc4: Get rid of the dsi->bridge field")
> > ---
> >  drivers/gpu/drm/vc4/vc4_dsi.c | 88 +++++++++++++++++++++--------------
> >  1 file changed, 52 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> > index c9ba83ed49b9..49f8a313e759 100644
> > --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> > +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> > @@ -498,7 +498,11 @@ struct vc4_dsi {
> >  
> >  	struct mipi_dsi_host dsi_host;
> >  	struct drm_encoder *encoder;
> > -	struct drm_bridge *bridge;
> > +
> > +	/* Embed a bridge object so we can implement bridge funcs instead of
> > +	 * encoder ones.
> > +	 */
> > +	struct drm_bridge bridge;
> >  
> >  	void __iomem *regs;
> >  
> > @@ -543,6 +547,11 @@ struct vc4_dsi {
> >  	struct debugfs_regset32 regset;
> >  };
> >  
> > +static inline struct vc4_dsi *bridge_to_vc4_dsi(struct drm_bridge *bridge)
> > +{
> > +	return container_of(bridge, struct vc4_dsi, bridge);
> > +}
> > +
> >  #define host_to_dsi(host) container_of(host, struct vc4_dsi, dsi_host)
> >  
> >  static inline void
> > @@ -747,16 +756,11 @@ dsi_esc_timing(u32 ns)
> >  	return DIV_ROUND_UP(ns, ESC_TIME_NS);
> >  }
> >  
> > -static void vc4_dsi_encoder_disable(struct drm_encoder *encoder)
> > +static void vc4_dsi_bridge_post_disable(struct drm_bridge *bridge)
> >  {
> > -	struct vc4_dsi_encoder *vc4_encoder = to_vc4_dsi_encoder(encoder);
> > -	struct vc4_dsi *dsi = vc4_encoder->dsi;
> > +	struct vc4_dsi *dsi = bridge_to_vc4_dsi(bridge);
> >  	struct device *dev = &dsi->pdev->dev;
> >  
> > -	drm_bridge_disable(dsi->bridge);
> > -	vc4_dsi_ulps(dsi, true);
> > -	drm_bridge_post_disable(dsi->bridge);
> > -
> >  	clk_disable_unprepare(dsi->pll_phy_clock);
> >  	clk_disable_unprepare(dsi->escape_clock);
> >  	clk_disable_unprepare(dsi->pixel_clock);
> > @@ -764,6 +768,13 @@ static void vc4_dsi_encoder_disable(struct drm_encoder *encoder)
> >  	pm_runtime_put(dev);
> >  }
> >  
> > +static void vc4_dsi_bridge_disable(struct drm_bridge *bridge)
> > +{
> > +	struct vc4_dsi *dsi = bridge_to_vc4_dsi(bridge);
> > +
> > +	vc4_dsi_ulps(dsi, true);
> > +}
> > +
> >  /* Extends the mode's blank intervals to handle BCM2835's integer-only
> >   * DSI PLL divider.
> >   *
> > @@ -777,12 +788,11 @@ static void vc4_dsi_encoder_disable(struct drm_encoder *encoder)
> >   * higher-than-expected clock rate to the panel, but that's what the
> >   * firmware does too.
> >   */
> > -static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder,
> > -				       const struct drm_display_mode *mode,
> > -				       struct drm_display_mode *adjusted_mode)
> > +static bool vc4_dsi_bridge_mode_fixup(struct drm_bridge *bridge,
> > +				      const struct drm_display_mode *mode,
> > +				      struct drm_display_mode *adjusted_mode)
> >  {
> > -	struct vc4_dsi_encoder *vc4_encoder = to_vc4_dsi_encoder(encoder);
> > -	struct vc4_dsi *dsi = vc4_encoder->dsi;
> > +	struct vc4_dsi *dsi = bridge_to_vc4_dsi(bridge);
> >  	struct clk *phy_parent = clk_get_parent(dsi->pll_phy_clock);
> >  	unsigned long parent_rate = clk_get_rate(phy_parent);
> >  	unsigned long pixel_clock_hz = mode->clock * 1000;
> > @@ -816,11 +826,11 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder,
> >  	return true;
> >  }
> >  
> > -static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
> > +static void vc4_dsi_bridge_pre_enable(struct drm_bridge *bridge)
> >  {
> > +	struct drm_encoder *encoder = bridge->encoder;
> >  	struct drm_display_mode *mode = &encoder->crtc->state->adjusted_mode;
> > -	struct vc4_dsi_encoder *vc4_encoder = to_vc4_dsi_encoder(encoder);
> > -	struct vc4_dsi *dsi = vc4_encoder->dsi;
> > +	struct vc4_dsi *dsi = bridge_to_vc4_dsi(bridge);
> >  	struct device *dev = &dsi->pdev->dev;
> >  	bool debug_dump_regs = false;
> >  	unsigned long hs_clock;
> > @@ -1054,8 +1064,12 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
> >  	}
> >  
> >  	vc4_dsi_ulps(dsi, false);
> > +}
> >  
> > -	drm_bridge_pre_enable(dsi->bridge);  
> 
> If I'm not mistaken this switches the order of the DSI's encoder
> pre-enable and the next bridge's pre-enable. I think it's true for
> post-disable too. It may not be a problem, but have this been tested ?


No, it hasn't been tested (I don't have a Rpi with a DSI panel at
hand), and now that you mention it, I don't think it will work (I had
forgotten drm_bridge_pre_enable() iterates the bridge chain in reverse
order).
Well, it will work if the DSI encoder is connected to the RPi DSI panel
since ->prepare() doesn't do anything, but I see that some DSI panel
drivers send DSI commands in their ->prepare() method (BTW, we should
really document the fact that panel drivers can send DSI commands in
the ->prepare() hook).

The only way this can be fixed is by putting the
vc4_dsi_pre_enable/post_disable() code in runtime PM resume/suspend
hooks and let the vc4_dsi_host_transfer() call pm_runtime_get_sync(),
pm_runtime_put() every time a msg is sent.

> 
> > +static void vc4_dsi_bridge_enable(struct drm_bridge *bridge)
> > +{
> > +	struct vc4_dsi *dsi = bridge_to_vc4_dsi(bridge);
> > +	bool debug_dump_regs = false;
> >  
> >  	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> >  		DSI_PORT_WRITE(DISP0_CTRL,
> > @@ -1072,8 +1086,6 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
> >  			       DSI_DISP0_ENABLE);
> >  	}
> >  
> > -	drm_bridge_enable(dsi->bridge);
> > -
> >  	if (debug_dump_regs) {
> >  		struct drm_printer p = drm_info_printer(&dsi->pdev->dev);
> >  		dev_info(&dsi->pdev->dev, "DSI regs after:\n");
> > @@ -1290,10 +1302,12 @@ static const struct mipi_dsi_host_ops vc4_dsi_host_ops = {
> >  	.transfer = vc4_dsi_host_transfer,
> >  };
> >  
> > -static const struct drm_encoder_helper_funcs vc4_dsi_encoder_helper_funcs = {
> > -	.disable = vc4_dsi_encoder_disable,
> > -	.enable = vc4_dsi_encoder_enable,
> > -	.mode_fixup = vc4_dsi_encoder_mode_fixup,
> > +static const struct drm_bridge_funcs vc4_dsi_bridge_funcs = {
> > +	.pre_enable = vc4_dsi_bridge_pre_enable,
> > +	.enable = vc4_dsi_bridge_enable,
> > +	.disable = vc4_dsi_bridge_disable,
> > +	.post_disable = vc4_dsi_bridge_post_disable,
> > +	.mode_fixup = vc4_dsi_bridge_mode_fixup,
> >  };
> >  
> >  static const struct of_device_id vc4_dsi_dt_match[] = {
> > @@ -1445,6 +1459,7 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
> >  	struct vc4_dev *vc4 = to_vc4_dev(drm);
> >  	struct vc4_dsi *dsi = dev_get_drvdata(dev);
> >  	struct vc4_dsi_encoder *vc4_dsi_encoder;
> > +	struct drm_bridge *next_bridge;
> >  	struct drm_panel *panel;
> >  	const struct of_device_id *match;
> >  	dma_cap_mask_t dma_mask;
> > @@ -1561,7 +1576,7 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
> >  	}
> >  
> >  	ret = drm_of_find_panel_or_bridge(dev->of_node, 0, 0,
> > -					  &panel, &dsi->bridge);
> > +					  &panel, &next_bridge);
> >  	if (ret) {
> >  		/* If the bridge or panel pointed by dev->of_node is not
> >  		 * enabled, just return 0 here so that we don't prevent the DRM
> > @@ -1576,10 +1591,10 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
> >  	}
> >  
> >  	if (panel) {
> > -		dsi->bridge = devm_drm_panel_bridge_add_typed(dev, panel,
> > +		next_bridge = devm_drm_panel_bridge_add_typed(dev, panel,
> >  							      DRM_MODE_CONNECTOR_DSI);
> > -		if (IS_ERR(dsi->bridge))
> > -			return PTR_ERR(dsi->bridge);
> > +		if (IS_ERR(next_bridge))
> > +			return PTR_ERR(next_bridge);
> >  	}
> >  
> >  	/* The esc clock rate is supposed to always be 100Mhz. */
> > @@ -1598,19 +1613,20 @@ static int vc4_dsi_bind(struct device *dev, struct device *master, void *data)
> >  
> >  	drm_encoder_init(drm, dsi->encoder, &vc4_dsi_encoder_funcs,
> >  			 DRM_MODE_ENCODER_DSI, NULL);
> > -	drm_encoder_helper_add(dsi->encoder, &vc4_dsi_encoder_helper_funcs);
> >  
> > -	ret = drm_bridge_attach(dsi->encoder, dsi->bridge, NULL);
> > +	/* Declare ourself as the first bridge element. */
> > +	dsi->bridge.funcs = &vc4_dsi_bridge_funcs;
> > +	ret = drm_bridge_attach(dsi->encoder, &dsi->bridge, NULL);
> > +	if (ret) {
> > +		dev_err(dev, "bridge attach failed: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	ret = drm_bridge_attach(dsi->encoder, next_bridge, &dsi->bridge);
> >  	if (ret) {
> >  		dev_err(dev, "bridge attach failed: %d\n", ret);
> >  		return ret;
> >  	}  
> 
> This is usually done in the bridge attach operation. As we're in control
> we can attach the next bridge here, but I think the driver would look
> more standard if you moved the second attach call to this bridge's
> attach operation.

I agree.

> 
> With this fixed, and if the driver has been tested and the
> enable/disable order change doesn't cause issues,
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> > -	/* Disable the atomic helper calls into the bridge.  We
> > -	 * manually call the bridge pre_enable / enable / etc. calls
> > -	 * from our driver, since we need to sequence them within the
> > -	 * encoder's enable/disable paths.
> > -	 */
> > -	dsi->encoder->bridge = NULL;
> >  
> >  	if (dsi->port == 0)
> >  		vc4_debugfs_add_regset32(drm, "dsi0_regs", &dsi->regset);
> > @@ -1629,7 +1645,7 @@ static void vc4_dsi_unbind(struct device *dev, struct device *master,
> >  	struct vc4_dev *vc4 = to_vc4_dev(drm);
> >  	struct vc4_dsi *dsi = dev_get_drvdata(dev);
> >  
> > -	if (dsi->bridge)
> > +	if (dsi->bridge.next)
> >  		pm_runtime_disable(dev);
> >  
> >  	vc4_dsi_encoder_destroy(dsi->encoder);  
> 

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