20.12.2021 13:48, Thierry Reding пишет: > From: Thierry Reding <treding@xxxxxxxxxx> > > Hi, > > this is an alternative proposal to fix panel support on Venice 2 and > Nyan. Dmitry had proposed a different solution that involved reverting > the I2C/DDC registration order and would complicate things by breaking > the encapsulation of the driver by introducing a global (though locally > scoped) variable[0]. > > This set of patches avoids that by using the recently introduced DP AUX > bus infrastructure. The result is that the changes are actually less > intrusive and not a step back. Instead they nicely remove the circular > dependency that previously existed and caused these issues in the first > place. > > To be fair, this is not perfect either because it requires a device tree > change and hence isn't technically backwards-compatible. However, given > that the original device tree was badly broken in the first place, I > think we can make an exception, especially since it is not generally a > problem to update device trees on the affected devices. > > Secondly, this relies on infrastructure that was introduced in v5.15 and > therefore will be difficult to backport beyond that. However, since this > functionality has been broken since v5.13 and all of the kernel versions > between that and v5.15 are EOL anyway, there isn't much that we can do > to fix the interim versions anyway. > > Adding Doug and Laurent since they originally designed the AUX bus > patches in case they see anything in here that would be objectionable. > > Thierry > > [0]: https://lore.kernel.org/dri-devel/20211130230957.30213-1-digetx@xxxxxxxxx/ > > Thierry Reding (2): > drm/tegra: dpaux: Populate AUX bus > ARM: tegra: Move panels to AUX bus > > arch/arm/boot/dts/tegra124-nyan-big.dts | 15 +++++++++------ > arch/arm/boot/dts/tegra124-nyan-blaze.dts | 15 +++++++++------ > arch/arm/boot/dts/tegra124-venice2.dts | 14 +++++++------- > drivers/gpu/drm/tegra/Kconfig | 1 + > drivers/gpu/drm/tegra/dpaux.c | 7 +++++++ > 5 files changed, 33 insertions(+), 19 deletions(-) > It should "work" since you removed the ddc-i2c-bus phandle from the panel nodes, and thus, panel->ddc won't be used during panel-edp driver probe. But this looks like a hack rather than a fix. I'm not sure why and how devm_of_dp_aux_populate_ep_devices() usage should be relevant here. The drm_dp_aux_register() still should to invoked before devm_of_dp_aux_populate_ep_devices(), otherwise panel->ddc adapter won't be registered. The panel->ddc isn't used by the new panel-edp driver unless panel is compatible with "edp-panel". Hence the generic_edp_panel_probe() should either fail or crash for a such "edp-panel" since panel->ddc isn't fully instantiated, AFAICS.
