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, 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
