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@xxxxxxxxx>
> > ---
> > 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/
