Re: [PATCH v4 00/24] drm/bridge: Make panel and bridge probe order consistent

[Laurent Pinchart]

Hi Maxime,

On Thu, Sep 30, 2021 at 12:56:02AM +0300, Laurent Pinchart wrote:
> On Fri, Sep 10, 2021 at 12:11:54PM +0200, Maxime Ripard wrote:
> > Hi,
> > 
> > We've encountered an issue with the RaspberryPi DSI panel that prevented the
> > whole display driver from probing.
> > 
> > The issue is described in detail in the commit 7213246a803f ("drm/vc4: dsi:
> > Only register our component once a DSI device is attached"), but the basic idea
> > is that since the panel is probed through i2c, there's no synchronization
> > between its probe and the registration of the MIPI-DSI host it's attached to.
> > 
> > We initially moved the component framework registration to the MIPI-DSI Host
> > attach hook to make sure we register our component only when we have a DSI
> > device attached to our MIPI-DSI host, and then use lookup our DSI device in our
> > bind hook.
> > 
> > However, all the DSI bridges controlled through i2c are only registering their
> > associated DSI device in their bridge attach hook, meaning with our change
> > above, we never got that far, and therefore ended up in the same situation than
> > the one we were trying to fix for panels.
> > 
> > The best practice to avoid those issues is to register its functions only after
> > all its dependencies are live. We also shouldn't wait any longer than we should
> > to play nice with the other components that are waiting for us, so in our case
> > that would mean moving the DSI device registration to the bridge probe.
> > 
> > I also had a look at all the DSI hosts, and it seems that exynos, kirin and msm
> > would be affected by this and wouldn't probe anymore after those changes.
> > Exynos and kirin seems to be simple enough for a mechanical change (that still
> > requires to be tested), but the changes in msm seemed to be far more important
> > and I wasn't confortable doing them.
> > 
> > Let me know what you think,
> 
> I've tested this series on my RPi CM4-based board, and there's a clear
> improvement: the sn65dsi83 now probes successfully !
> 
> The downside is that I can now look at a panel that desperately refuses
> to display anything. That's a separate issue, but it prevents me from
> telling whether this series introduces regressions :-S I'll try to debug
> that separately.

I managed to (partly) fix that issue with a few backports from the RPi
kernel, making me confident enough to say

Tested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

for

drivers/gpu/drm/bridge/ti-sn65dsi83.c
drivers/gpu/drm/drm_bridge.c
drivers/gpu/drm/drm_mipi_dsi.c
include/drm/drm_mipi_dsi.h

> Also, Kieran, would you be able to test this with the SN65DSI86 ?
> 
> > ---
> > 
> > Changes from v3:
> >   - Converted exynos and kirin
> >   - Converted all the affected bridge drivers
> >   - Reworded the documentation a bit
> > 
> > Changes from v2:
> >   - Changed the approach as suggested by Andrzej, and aligned the bridge on the
> >     panel this time.
> >   - Fixed some typos
> > 
> > Changes from v1:
> >   - Change the name of drm_of_get_next function to drm_of_get_bridge
> >   - Mention the revert of 87154ff86bf6 and squash the two patches that were
> >     reverting that commit
> >   - Add some documentation
> >   - Make drm_panel_attach and _detach succeed when no callback is there
> > 
> > Maxime Ripard (24):
> >   drm/bridge: Add documentation sections
> >   drm/bridge: Document the probe issue with MIPI-DSI bridges
> >   drm/mipi-dsi: Create devm device registration
> >   drm/mipi-dsi: Create devm device attachment
> >   drm/bridge: adv7533: Switch to devm MIPI-DSI helpers
> >   drm/bridge: adv7511: Register and attach our DSI device at probe
> >   drm/bridge: anx7625: Switch to devm MIPI-DSI helpers
> >   drm/bridge: anx7625: Register and attach our DSI device at probe
> >   drm/bridge: lt8912b: Switch to devm MIPI-DSI helpers
> >   drm/bridge: lt8912b: Register and attach our DSI device at probe
> >   drm/bridge: lt9611: Switch to devm MIPI-DSI helpers
> >   drm/bridge: lt9611: Register and attach our DSI device at probe
> >   drm/bridge: lt9611uxc: Switch to devm MIPI-DSI helpers
> >   drm/bridge: lt9611uxc: Register and attach our DSI device at probe
> >   drm/bridge: ps8640: Switch to devm MIPI-DSI helpers
> >   drm/bridge: ps8640: Register and attach our DSI device at probe
> >   drm/bridge: sn65dsi83: Switch to devm MIPI-DSI helpers
> >   drm/bridge: sn65dsi83: Register and attach our DSI device at probe
> >   drm/bridge: sn65dsi86: Switch to devm MIPI-DSI helpers
> >   drm/bridge: sn65dsi86: Register and attach our DSI device at probe
> >   drm/bridge: tc358775: Switch to devm MIPI-DSI helpers
> >   drm/bridge: tc358775: Register and attach our DSI device at probe
> >   drm/kirin: dsi: Adjust probe order
> >   drm/exynos: dsi: Adjust probe order
> > 
> >  Documentation/gpu/drm-kms-helpers.rst        |  12 +++
> >  drivers/gpu/drm/bridge/adv7511/adv7511.h     |   1 -
> >  drivers/gpu/drm/bridge/adv7511/adv7511_drv.c |  15 ++-
> >  drivers/gpu/drm/bridge/adv7511/adv7533.c     |  20 +---
> >  drivers/gpu/drm/bridge/analogix/anx7625.c    |  40 ++++----
> >  drivers/gpu/drm/bridge/lontium-lt8912b.c     |  31 ++----
> >  drivers/gpu/drm/bridge/lontium-lt9611.c      |  62 +++++-------
> >  drivers/gpu/drm/bridge/lontium-lt9611uxc.c   |  65 +++++-------
> >  drivers/gpu/drm/bridge/parade-ps8640.c       | 101 ++++++++++---------
> >  drivers/gpu/drm/bridge/tc358775.c            |  50 +++++----
> >  drivers/gpu/drm/bridge/ti-sn65dsi83.c        |  86 ++++++++--------
> >  drivers/gpu/drm/bridge/ti-sn65dsi86.c        |  94 ++++++++---------
> >  drivers/gpu/drm/drm_bridge.c                 |  69 ++++++++++++-
> >  drivers/gpu/drm/drm_mipi_dsi.c               |  81 +++++++++++++++
> >  drivers/gpu/drm/exynos/exynos_drm_dsi.c      |  19 ++--
> >  drivers/gpu/drm/hisilicon/kirin/dw_drm_dsi.c |  27 +++--
> >  include/drm/drm_mipi_dsi.h                   |   4 +
> >  17 files changed, 460 insertions(+), 317 deletions(-)

-- 
Regards,

Laurent Pinchart