[PATCH v3 3/8] drm/bridge/synopsys: dsi: add ability to check dsi-device attachment

[Heiko Stuebner]

Hi Andrzej,

Am Montag, 13. August 2018, 10:28:39 CEST schrieb Andrzej Hajda:
> On 09.07.2018 15:48, Heiko Stuebner wrote:
> > When the panel-driver is build as a module it currently fails hard as the
> > panel cannot be probed directly:
> >
> > dw_mipi_dsi_bind()
> >   __dw_mipi_dsi_probe()
> >     creates dsi bus
> >     creates panel device
> >     triggers panel module load
> >     panel not probed (module not loaded or panel probe slow)
> >   drm_bridge_attach
> >     fails with -EINVAL due to empty panel_bridge
> >
> > Additionally the panel probing can run concurrently with dsi bringup
> > making it possible that the panel can already be found but dsi-attach
> > hasn't finished running.
> >
> > The newly added function provides the ability for glue drivers to
> > check if a dsi device was actually attached and also protects
> > the attach part to prevent concurrency issues from panel-assignment
> > and drm_bridge_create.
> >
> > Using that check glue drivers are able to for example defer probe/bind
> > in the case that the panel is not completely set up yet.
> >
> > Signed-off-by: Heiko Stuebner <heiko at sntech.de>
> > ---
> >  drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 25 +++++++++++++++++++
> >  include/drm/bridge/dw_mipi_dsi.h              |  1 +
> >  2 files changed, 26 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > index bb4aeca5c0f9..88fed22ff3f6 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/component.h>
> >  #include <linux/iopoll.h>
> >  #include <linux/module.h>
> > +#include <linux/mutex.h>
> >  #include <linux/of_device.h>
> >  #include <linux/pm_runtime.h>
> >  #include <linux/reset.h>
> > @@ -219,6 +220,7 @@ struct dw_mipi_dsi {
> >  	struct drm_bridge bridge;
> >  	struct mipi_dsi_host dsi_host;
> >  	struct drm_bridge *panel_bridge;
> > +	struct mutex panel_mutex;
> >  	struct device *dev;
> >  	void __iomem *base;
> >  
> > @@ -296,10 +298,14 @@ static int dw_mipi_dsi_host_attach(struct mipi_dsi_host *host,
> >  			return PTR_ERR(bridge);
> >  	}
> >  
> > +	mutex_lock(&dsi->panel_mutex);
> > +
> >  	dsi->panel_bridge = bridge;
> >  
> >  	drm_bridge_add(&dsi->bridge);
> >  
> > +	mutex_unlock(&dsi->panel_mutex);
> > +
> >  	return 0;
> >  }
> >  
> > @@ -308,13 +314,30 @@ static int dw_mipi_dsi_host_detach(struct mipi_dsi_host *host,
> >  {
> >  	struct dw_mipi_dsi *dsi = host_to_dsi(host);
> >  
> > +	mutex_lock(&dsi->panel_mutex);
> > +
> > +	dsi->panel_bridge = NULL;
> >  	drm_of_panel_bridge_remove(host->dev->of_node, 1, 0);
> >  
> >  	drm_bridge_remove(&dsi->bridge);
> >  
> > +	mutex_unlock(&dsi->panel_mutex);
> > +
> >  	return 0;
> >  }
> >  
> > +bool dw_mipi_dsi_device_attached(struct dw_mipi_dsi *dsi)
> > +{
> > +	bool output;
> > +
> > +	mutex_lock(&dsi->panel_mutex);
> > +	output = !!dsi->panel_bridge;
> > +	mutex_unlock(&dsi->panel_mutex);
> > +
> > +	return output;
> > +}
> > +EXPORT_SYMBOL_GPL(dw_mipi_dsi_device_attached);
> 
> The function does not make sense. After releasing panel_mutex device can
> be detached/(re-)attached multiple times. Ie it reports useless
> information. Of course in most cases it will work as expected, but for
> sure it is not bulletproof.

Ok. Can you suggest how we should check for the described case?
I.e. initially I tried to simply defer in dw_mipi_dsi_bridge_attach [0]
where you suggested to do that in probe.

I moved the check to bind - see patch 5 - to fix the issue regarding
panel only probing after the dsi bus gets created, so this function
is a means to check if the panel has finished attaching, or to defer
binding - see dw_mipi_dsi_rockchip_bind in patch 5.

So I'm somewhat out of ideas right now, how to do this right.


Thanks
Heiko

[0] https://patchwork.kernel.org/patch/10470821/