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@xxxxxxxxxx> > >>> --- > >>> 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@xxxxxxxxxxx> > > 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
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