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

[Laurent Pinchart]

Hi Maxime,

(CC'ing Kieran)

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.

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