| Message ID | 20210910101218.1632297-3-maxime@cerno.tech (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | drm/bridge: Make panel and bridge probe order consistent | expand |
W dniu 10.09.2021 o 12:11, Maxime Ripard pisze: > Interactions between bridges, panels, MIPI-DSI host and the component > framework are not trivial and can lead to probing issues when > implementing a display driver. Let's document the various cases we need > too consider, and the solution to support all the cases. > > Signed-off-by: Maxime Ripard <maxime@cerno.tech> > --- > Documentation/gpu/drm-kms-helpers.rst | 6 +++ > drivers/gpu/drm/drm_bridge.c | 57 +++++++++++++++++++++++++++ > 2 files changed, 63 insertions(+) > > diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst > index 10f8df7aecc0..ec2f65b31930 100644 > --- a/Documentation/gpu/drm-kms-helpers.rst > +++ b/Documentation/gpu/drm-kms-helpers.rst > @@ -157,6 +157,12 @@ Display Driver Integration > .. kernel-doc:: drivers/gpu/drm/drm_bridge.c > :doc: display driver integration > > +Special Care with MIPI-DSI bridges > +---------------------------------- > + > +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c > + :doc: special care dsi > + > Bridge Operations > ----------------- > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > index baff74ea4a33..7cc2d2f94ae3 100644 > --- a/drivers/gpu/drm/drm_bridge.c > +++ b/drivers/gpu/drm/drm_bridge.c > @@ -96,6 +96,63 @@ > * documentation of bridge operations for more details). > */ > > +/** > + * DOC: special care dsi > + * > + * The interaction between the bridges and other frameworks involved in > + * the probing of the upstream driver and the bridge driver can be > + * challenging. Indeed, there's multiple cases that needs to be > + * considered: > + * > + * - The upstream driver doesn't use the component framework and isn't a > + * MIPI-DSI host. In this case, the bridge driver will probe at some > + * point and the upstream driver should try to probe again by returning > + * EPROBE_DEFER as long as the bridge driver hasn't probed. > + * > + * - The upstream driver doesn't use the component framework, but is a > + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be > + * controlled. In this case, the bridge device is a child of the > + * display device and when it will probe it's assured that the display > + * device (and MIPI-DSI host) is present. The upstream driver will be > + * assured that the bridge driver is connected between the > + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operations. > + * Therefore, it must run mipi_dsi_host_register() in its probe > + * function, and then run drm_bridge_attach() in its > + * &mipi_dsi_host_ops.attach hook. > + * > + * - The upstream driver uses the component framework and is a MIPI-DSI > + * host. The bridge device uses the MIPI-DCS commands to be > + * controlled. This is the same situation than above, and can run > + * mipi_dsi_host_register() in either its probe or bind hooks. > + * > + * - The upstream driver uses the component framework and is a MIPI-DSI > + * host. The bridge device uses a separate bus (such as I2C) to be > + * controlled. In this case, there's no correlation between the probe > + * of the bridge and upstream drivers, so care must be taken to avoid > + * an endless EPROBE_DEFER loop, with each driver waiting for the > + * other to probe. > + * > + * The ideal pattern to cover the last item (and all the others in the > + * MIPI-DSI host driver case) is to split the operations like this: > + * > + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in its > + * probe hook. It will make sure that the MIPI-DSI host sticks around, > + * and that the driver's bind can be called. > + * > + * - In its probe hook, the bridge driver must try to find its MIPI-DSI > + * host, register as a MIPI-DSI device and attach the MIPI-DSI device > + * to its host. The bridge driver is now functional. > + * > + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host can > + * now add its component. Its bind hook will now be called and since > + * the bridge driver is attached and registered, we can now look for > + * and attach it. > + * > + * At this point, we're now certain that both the upstream driver and > + * the bridge driver are functional and we can't have a deadlock-like > + * situation when probing. > + */ > + > static DEFINE_MUTEX(bridge_lock); > static LIST_HEAD(bridge_list); > Nice work with documenting this initialization dance. It clearly shows that bridge API lacks better mechanism - usage of mipi dsi callbacks to get notifications about bridge appearance is ugly. It remains me my resource tracking patches which I have posted long time ago [1] - they would solve the issue in much more elegant way, described here [2]. Apparently I was not stubborn enough in promoting this solution. Anyway: Reviewed-by: Andrzej Hajda <a.hajda@samsung.com> [1]: https://lkml.org/lkml/2014/12/10/342 [2]: https://events19.linuxfoundation.org/wp-content/uploads/2017/12/Deferred-Problem-Issues-With-Complex-Dependencies-Between-Devices-in-Linux-Kernel-Andrzej-Hajda-Samsung.pdf Regards Andrzej
Hi, On Mon, Sep 13, 2021 at 08:29:37AM +0200, Andrzej Hajda wrote: > > W dniu 10.09.2021 o 12:11, Maxime Ripard pisze: > > Interactions between bridges, panels, MIPI-DSI host and the component > > framework are not trivial and can lead to probing issues when > > implementing a display driver. Let's document the various cases we need > > too consider, and the solution to support all the cases. > > > > Signed-off-by: Maxime Ripard <maxime@cerno.tech> > > --- > > Documentation/gpu/drm-kms-helpers.rst | 6 +++ > > drivers/gpu/drm/drm_bridge.c | 57 +++++++++++++++++++++++++++ > > 2 files changed, 63 insertions(+) > > > > diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst > > index 10f8df7aecc0..ec2f65b31930 100644 > > --- a/Documentation/gpu/drm-kms-helpers.rst > > +++ b/Documentation/gpu/drm-kms-helpers.rst > > @@ -157,6 +157,12 @@ Display Driver Integration > > .. kernel-doc:: drivers/gpu/drm/drm_bridge.c > > :doc: display driver integration > > > > +Special Care with MIPI-DSI bridges > > +---------------------------------- > > + > > +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c > > + :doc: special care dsi > > + > > Bridge Operations > > ----------------- > > > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > > index baff74ea4a33..7cc2d2f94ae3 100644 > > --- a/drivers/gpu/drm/drm_bridge.c > > +++ b/drivers/gpu/drm/drm_bridge.c > > @@ -96,6 +96,63 @@ > > * documentation of bridge operations for more details). > > */ > > > > +/** > > + * DOC: special care dsi > > + * > > + * The interaction between the bridges and other frameworks involved in > > + * the probing of the upstream driver and the bridge driver can be > > + * challenging. Indeed, there's multiple cases that needs to be > > + * considered: > > + * > > + * - The upstream driver doesn't use the component framework and isn't a > > + * MIPI-DSI host. In this case, the bridge driver will probe at some > > + * point and the upstream driver should try to probe again by returning > > + * EPROBE_DEFER as long as the bridge driver hasn't probed. > > + * > > + * - The upstream driver doesn't use the component framework, but is a > > + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be > > + * controlled. In this case, the bridge device is a child of the > > + * display device and when it will probe it's assured that the display > > + * device (and MIPI-DSI host) is present. The upstream driver will be > > + * assured that the bridge driver is connected between the > > + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operations. > > + * Therefore, it must run mipi_dsi_host_register() in its probe > > + * function, and then run drm_bridge_attach() in its > > + * &mipi_dsi_host_ops.attach hook. > > + * > > + * - The upstream driver uses the component framework and is a MIPI-DSI > > + * host. The bridge device uses the MIPI-DCS commands to be > > + * controlled. This is the same situation than above, and can run > > + * mipi_dsi_host_register() in either its probe or bind hooks. > > + * > > + * - The upstream driver uses the component framework and is a MIPI-DSI > > + * host. The bridge device uses a separate bus (such as I2C) to be > > + * controlled. In this case, there's no correlation between the probe > > + * of the bridge and upstream drivers, so care must be taken to avoid > > + * an endless EPROBE_DEFER loop, with each driver waiting for the > > + * other to probe. > > + * > > + * The ideal pattern to cover the last item (and all the others in the > > + * MIPI-DSI host driver case) is to split the operations like this: > > + * > > + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in its > > + * probe hook. It will make sure that the MIPI-DSI host sticks around, > > + * and that the driver's bind can be called. > > + * > > + * - In its probe hook, the bridge driver must try to find its MIPI-DSI > > + * host, register as a MIPI-DSI device and attach the MIPI-DSI device > > + * to its host. The bridge driver is now functional. > > + * > > + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host can > > + * now add its component. Its bind hook will now be called and since > > + * the bridge driver is attached and registered, we can now look for > > + * and attach it. > > + * > > + * At this point, we're now certain that both the upstream driver and > > + * the bridge driver are functional and we can't have a deadlock-like > > + * situation when probing. > > + */ > > + > > static DEFINE_MUTEX(bridge_lock); > > static LIST_HEAD(bridge_list); > > > Nice work with documenting this initialization dance. It clearly shows > that bridge API lacks better mechanism - usage of mipi dsi callbacks to > get notifications about bridge appearance is ugly. Yeah, there's so many moving parts it's definitely not great. > It remains me my resource tracking patches which I have posted long > time ago [1] - they would solve the issue in much more elegant way, > described here [2]. Apparently I was not stubborn enough in promoting > this solution. Wow, that sounds like a massive change indeed :/ > Anyway: > > Reviewed-by: Andrzej Hajda <a.hajda@samsung.com> I assume you'll want me to hold off that patch before someone reviews the rest? Thanks! Maxime
W dniu 14.09.2021 o 16:35, Maxime Ripard pisze: > Hi, > > On Mon, Sep 13, 2021 at 08:29:37AM +0200, Andrzej Hajda wrote: >> W dniu 10.09.2021 o 12:11, Maxime Ripard pisze: >>> Interactions between bridges, panels, MIPI-DSI host and the component >>> framework are not trivial and can lead to probing issues when >>> implementing a display driver. Let's document the various cases we need >>> too consider, and the solution to support all the cases. >>> >>> Signed-off-by: Maxime Ripard <maxime@cerno.tech> >>> --- >>> Documentation/gpu/drm-kms-helpers.rst | 6 +++ >>> drivers/gpu/drm/drm_bridge.c | 57 +++++++++++++++++++++++++++ >>> 2 files changed, 63 insertions(+) >>> >>> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst >>> index 10f8df7aecc0..ec2f65b31930 100644 >>> --- a/Documentation/gpu/drm-kms-helpers.rst >>> +++ b/Documentation/gpu/drm-kms-helpers.rst >>> @@ -157,6 +157,12 @@ Display Driver Integration >>> .. kernel-doc:: drivers/gpu/drm/drm_bridge.c >>> :doc: display driver integration >>> >>> +Special Care with MIPI-DSI bridges >>> +---------------------------------- >>> + >>> +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c >>> + :doc: special care dsi >>> + >>> Bridge Operations >>> ----------------- >>> >>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c >>> index baff74ea4a33..7cc2d2f94ae3 100644 >>> --- a/drivers/gpu/drm/drm_bridge.c >>> +++ b/drivers/gpu/drm/drm_bridge.c >>> @@ -96,6 +96,63 @@ >>> * documentation of bridge operations for more details). >>> */ >>> >>> +/** >>> + * DOC: special care dsi >>> + * >>> + * The interaction between the bridges and other frameworks involved in >>> + * the probing of the upstream driver and the bridge driver can be >>> + * challenging. Indeed, there's multiple cases that needs to be >>> + * considered: >>> + * >>> + * - The upstream driver doesn't use the component framework and isn't a >>> + * MIPI-DSI host. In this case, the bridge driver will probe at some >>> + * point and the upstream driver should try to probe again by returning >>> + * EPROBE_DEFER as long as the bridge driver hasn't probed. >>> + * >>> + * - The upstream driver doesn't use the component framework, but is a >>> + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be >>> + * controlled. In this case, the bridge device is a child of the >>> + * display device and when it will probe it's assured that the display >>> + * device (and MIPI-DSI host) is present. The upstream driver will be >>> + * assured that the bridge driver is connected between the >>> + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operations. >>> + * Therefore, it must run mipi_dsi_host_register() in its probe >>> + * function, and then run drm_bridge_attach() in its >>> + * &mipi_dsi_host_ops.attach hook. >>> + * >>> + * - The upstream driver uses the component framework and is a MIPI-DSI >>> + * host. The bridge device uses the MIPI-DCS commands to be >>> + * controlled. This is the same situation than above, and can run >>> + * mipi_dsi_host_register() in either its probe or bind hooks. >>> + * >>> + * - The upstream driver uses the component framework and is a MIPI-DSI >>> + * host. The bridge device uses a separate bus (such as I2C) to be >>> + * controlled. In this case, there's no correlation between the probe >>> + * of the bridge and upstream drivers, so care must be taken to avoid >>> + * an endless EPROBE_DEFER loop, with each driver waiting for the >>> + * other to probe. >>> + * >>> + * The ideal pattern to cover the last item (and all the others in the >>> + * MIPI-DSI host driver case) is to split the operations like this: >>> + * >>> + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in its >>> + * probe hook. It will make sure that the MIPI-DSI host sticks around, >>> + * and that the driver's bind can be called. >>> + * >>> + * - In its probe hook, the bridge driver must try to find its MIPI-DSI >>> + * host, register as a MIPI-DSI device and attach the MIPI-DSI device >>> + * to its host. The bridge driver is now functional. >>> + * >>> + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host can >>> + * now add its component. Its bind hook will now be called and since >>> + * the bridge driver is attached and registered, we can now look for >>> + * and attach it. >>> + * >>> + * At this point, we're now certain that both the upstream driver and >>> + * the bridge driver are functional and we can't have a deadlock-like >>> + * situation when probing. >>> + */ >>> + >>> static DEFINE_MUTEX(bridge_lock); >>> static LIST_HEAD(bridge_list); >> >> Nice work with documenting this initialization dance. It clearly shows >> that bridge API lacks better mechanism - usage of mipi dsi callbacks to >> get notifications about bridge appearance is ugly. > Yeah, there's so many moving parts it's definitely not great. > >> It remains me my resource tracking patches which I have posted long >> time ago [1] - they would solve the issue in much more elegant way, >> described here [2]. Apparently I was not stubborn enough in promoting >> this solution. > Wow, that sounds like a massive change indeed :/ > >> Anyway: >> >> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com> > I assume you'll want me to hold off that patch before someone reviews > the rest? The last exynos patch should be dropped, kirin patch should be tested/reviewed/acked by kirin maintaner. I am not sure about bridge patches, which ones have been tested by you, and which one have other users. If yes it would be good to test them as well - changes in initialization flow can beat sometimes :) I think patches 1-4 can be merged earlier, if you like, as they are on the list for long time. Regards Andrzej > > Thanks! > Maxime
Hi, On Tue, Sep 14, 2021 at 09:00:28PM +0200, Andrzej Hajda wrote: > > W dniu 14.09.2021 o 16:35, Maxime Ripard pisze: > > Hi, > > > > On Mon, Sep 13, 2021 at 08:29:37AM +0200, Andrzej Hajda wrote: > >> W dniu 10.09.2021 o 12:11, Maxime Ripard pisze: > >>> Interactions between bridges, panels, MIPI-DSI host and the component > >>> framework are not trivial and can lead to probing issues when > >>> implementing a display driver. Let's document the various cases we need > >>> too consider, and the solution to support all the cases. > >>> > >>> Signed-off-by: Maxime Ripard <maxime@cerno.tech> > >>> --- > >>> Documentation/gpu/drm-kms-helpers.rst | 6 +++ > >>> drivers/gpu/drm/drm_bridge.c | 57 +++++++++++++++++++++++++++ > >>> 2 files changed, 63 insertions(+) > >>> > >>> diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst > >>> index 10f8df7aecc0..ec2f65b31930 100644 > >>> --- a/Documentation/gpu/drm-kms-helpers.rst > >>> +++ b/Documentation/gpu/drm-kms-helpers.rst > >>> @@ -157,6 +157,12 @@ Display Driver Integration > >>> .. kernel-doc:: drivers/gpu/drm/drm_bridge.c > >>> :doc: display driver integration > >>> > >>> +Special Care with MIPI-DSI bridges > >>> +---------------------------------- > >>> + > >>> +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c > >>> + :doc: special care dsi > >>> + > >>> Bridge Operations > >>> ----------------- > >>> > >>> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c > >>> index baff74ea4a33..7cc2d2f94ae3 100644 > >>> --- a/drivers/gpu/drm/drm_bridge.c > >>> +++ b/drivers/gpu/drm/drm_bridge.c > >>> @@ -96,6 +96,63 @@ > >>> * documentation of bridge operations for more details). > >>> */ > >>> > >>> +/** > >>> + * DOC: special care dsi > >>> + * > >>> + * The interaction between the bridges and other frameworks involved in > >>> + * the probing of the upstream driver and the bridge driver can be > >>> + * challenging. Indeed, there's multiple cases that needs to be > >>> + * considered: > >>> + * > >>> + * - The upstream driver doesn't use the component framework and isn't a > >>> + * MIPI-DSI host. In this case, the bridge driver will probe at some > >>> + * point and the upstream driver should try to probe again by returning > >>> + * EPROBE_DEFER as long as the bridge driver hasn't probed. > >>> + * > >>> + * - The upstream driver doesn't use the component framework, but is a > >>> + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be > >>> + * controlled. In this case, the bridge device is a child of the > >>> + * display device and when it will probe it's assured that the display > >>> + * device (and MIPI-DSI host) is present. The upstream driver will be > >>> + * assured that the bridge driver is connected between the > >>> + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operations. > >>> + * Therefore, it must run mipi_dsi_host_register() in its probe > >>> + * function, and then run drm_bridge_attach() in its > >>> + * &mipi_dsi_host_ops.attach hook. > >>> + * > >>> + * - The upstream driver uses the component framework and is a MIPI-DSI > >>> + * host. The bridge device uses the MIPI-DCS commands to be > >>> + * controlled. This is the same situation than above, and can run > >>> + * mipi_dsi_host_register() in either its probe or bind hooks. > >>> + * > >>> + * - The upstream driver uses the component framework and is a MIPI-DSI > >>> + * host. The bridge device uses a separate bus (such as I2C) to be > >>> + * controlled. In this case, there's no correlation between the probe > >>> + * of the bridge and upstream drivers, so care must be taken to avoid > >>> + * an endless EPROBE_DEFER loop, with each driver waiting for the > >>> + * other to probe. > >>> + * > >>> + * The ideal pattern to cover the last item (and all the others in the > >>> + * MIPI-DSI host driver case) is to split the operations like this: > >>> + * > >>> + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in its > >>> + * probe hook. It will make sure that the MIPI-DSI host sticks around, > >>> + * and that the driver's bind can be called. > >>> + * > >>> + * - In its probe hook, the bridge driver must try to find its MIPI-DSI > >>> + * host, register as a MIPI-DSI device and attach the MIPI-DSI device > >>> + * to its host. The bridge driver is now functional. > >>> + * > >>> + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host can > >>> + * now add its component. Its bind hook will now be called and since > >>> + * the bridge driver is attached and registered, we can now look for > >>> + * and attach it. > >>> + * > >>> + * At this point, we're now certain that both the upstream driver and > >>> + * the bridge driver are functional and we can't have a deadlock-like > >>> + * situation when probing. > >>> + */ > >>> + > >>> static DEFINE_MUTEX(bridge_lock); > >>> static LIST_HEAD(bridge_list); > >> > >> Nice work with documenting this initialization dance. It clearly shows > >> that bridge API lacks better mechanism - usage of mipi dsi callbacks to > >> get notifications about bridge appearance is ugly. > > Yeah, there's so many moving parts it's definitely not great. > > > >> It remains me my resource tracking patches which I have posted long > >> time ago [1] - they would solve the issue in much more elegant way, > >> described here [2]. Apparently I was not stubborn enough in promoting > >> this solution. > > Wow, that sounds like a massive change indeed :/ > > > >> Anyway: > >> > >> Reviewed-by: Andrzej Hajda <a.hajda@samsung.com> > > I assume you'll want me to hold off that patch before someone reviews > > the rest? > > The last exynos patch should be dropped, Done > kirin patch should be tested/reviewed/acked by kirin maintaner. I am > not sure about bridge patches, which ones have been tested by you, and > which one have other users. Rob was nice enough to give it a try last week for msm and do the needed changes. He tested it with the sn65dsi86 bridge. John was also saying it was on their todo list (for kirin I assume?). So hopefully it can be fairly smooth for everyone. I tested sn65dsi83 and ps8640 with the vc4 driver. I don't have the hardware so it was just making sure that everything was probing properly, but it's what we're interested in anyway. > If yes it would be good to test them as well - changes in initialization > flow can beat sometimes :) > > I think patches 1-4 can be merged earlier, if you like, as they are on > the list for long time. Ack, I'll merge them, thanks! Maxime
On Fri, 10 Sep 2021 12:11:56 +0200, Maxime Ripard wrote: > Interactions between bridges, panels, MIPI-DSI host and the component > framework are not trivial and can lead to probing issues when > implementing a display driver. Let's document the various cases we need > too consider, and the solution to support all the cases. > > Applied to drm/drm-misc (drm-misc-next). Thanks! Maxime
diff --git a/Documentation/gpu/drm-kms-helpers.rst b/Documentation/gpu/drm-kms-helpers.rst index 10f8df7aecc0..ec2f65b31930 100644 --- a/Documentation/gpu/drm-kms-helpers.rst +++ b/Documentation/gpu/drm-kms-helpers.rst @@ -157,6 +157,12 @@ Display Driver Integration .. kernel-doc:: drivers/gpu/drm/drm_bridge.c :doc: display driver integration +Special Care with MIPI-DSI bridges +---------------------------------- + +.. kernel-doc:: drivers/gpu/drm/drm_bridge.c + :doc: special care dsi + Bridge Operations ----------------- diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index baff74ea4a33..7cc2d2f94ae3 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -96,6 +96,63 @@ * documentation of bridge operations for more details). */ +/** + * DOC: special care dsi + * + * The interaction between the bridges and other frameworks involved in + * the probing of the upstream driver and the bridge driver can be + * challenging. Indeed, there's multiple cases that needs to be + * considered: + * + * - The upstream driver doesn't use the component framework and isn't a + * MIPI-DSI host. In this case, the bridge driver will probe at some + * point and the upstream driver should try to probe again by returning + * EPROBE_DEFER as long as the bridge driver hasn't probed. + * + * - The upstream driver doesn't use the component framework, but is a + * MIPI-DSI host. The bridge device uses the MIPI-DCS commands to be + * controlled. In this case, the bridge device is a child of the + * display device and when it will probe it's assured that the display + * device (and MIPI-DSI host) is present. The upstream driver will be + * assured that the bridge driver is connected between the + * &mipi_dsi_host_ops.attach and &mipi_dsi_host_ops.detach operations. + * Therefore, it must run mipi_dsi_host_register() in its probe + * function, and then run drm_bridge_attach() in its + * &mipi_dsi_host_ops.attach hook. + * + * - The upstream driver uses the component framework and is a MIPI-DSI + * host. The bridge device uses the MIPI-DCS commands to be + * controlled. This is the same situation than above, and can run + * mipi_dsi_host_register() in either its probe or bind hooks. + * + * - The upstream driver uses the component framework and is a MIPI-DSI + * host. The bridge device uses a separate bus (such as I2C) to be + * controlled. In this case, there's no correlation between the probe + * of the bridge and upstream drivers, so care must be taken to avoid + * an endless EPROBE_DEFER loop, with each driver waiting for the + * other to probe. + * + * The ideal pattern to cover the last item (and all the others in the + * MIPI-DSI host driver case) is to split the operations like this: + * + * - The MIPI-DSI host driver must run mipi_dsi_host_register() in its + * probe hook. It will make sure that the MIPI-DSI host sticks around, + * and that the driver's bind can be called. + * + * - In its probe hook, the bridge driver must try to find its MIPI-DSI + * host, register as a MIPI-DSI device and attach the MIPI-DSI device + * to its host. The bridge driver is now functional. + * + * - In its &struct mipi_dsi_host_ops.attach hook, the MIPI-DSI host can + * now add its component. Its bind hook will now be called and since + * the bridge driver is attached and registered, we can now look for + * and attach it. + * + * At this point, we're now certain that both the upstream driver and + * the bridge driver are functional and we can't have a deadlock-like + * situation when probing. + */ + static DEFINE_MUTEX(bridge_lock); static LIST_HEAD(bridge_list);
Interactions between bridges, panels, MIPI-DSI host and the component framework are not trivial and can lead to probing issues when implementing a display driver. Let's document the various cases we need too consider, and the solution to support all the cases. Signed-off-by: Maxime Ripard <maxime@cerno.tech> --- Documentation/gpu/drm-kms-helpers.rst | 6 +++ drivers/gpu/drm/drm_bridge.c | 57 +++++++++++++++++++++++++++ 2 files changed, 63 insertions(+)