Re: [PATCH v1 2/2] drm/tegra: Use drm_dp_aux_register_ddc/chardev() helpers

Daniel Vetter
2021-11-08T15:17:43Z

On Mon, Nov 08, 2021 at 02:08:21AM +0300, Dmitry Osipenko wrote:
> Use drm_dp_aux_register_ddc/chardev() helpers that allow to register I2C
> adapter separately from the character device. This fixes broken display
> panel driver of Acer Chromebook CB5-311 that fails to probe starting with
> v5.13 kernel when DP AUX registration order was changed. Tegra SOR driver
> is never probed now using the new registration order because tegra-output
> always fails with -EPROBE_DEFER due to missing display panel that requires
> DP AUX DDC to be registered first. The offending commit made DDC to be
> registered after SOR's output, which can't ever happen. Use new helpers
> to restore the registration order and revive display panel.

This feels a bit backward, I think the clean solution would be to untangle
the SOR loading from the panel driver loading, and then only block
registering the overall drm_device on both drivers having loaded.

This here at least feels like a game of whack-a-mole, if like every driver
needs its own careful staging of everything.
-Daniel

>
> Cc: <stable@vger.kernel.org> # 5.13+
> Fixes: 39c17ae60ea9 ("drm/tegra: Don't register DP AUX channels before connectors")
> Reported-by: Thomas Graichen <thomas.graichen@gmail.com> # T124 Nyan Big
> Tested-by: Thomas Graichen <thomas.graichen@gmail.com> # T124 Nyan Big
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
> drivers/gpu/drm/tegra/dpaux.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
> index 1f96e416fa08..e0d675c7c2e5 100644
> --- a/drivers/gpu/drm/tegra/dpaux.c
> +++ b/drivers/gpu/drm/tegra/dpaux.c
> @@ -532,7 +532,9 @@ static int tegra_dpaux_probe(struct platform_device *pdev)
> dpaux->aux.transfer = tegra_dpaux_transfer;
> dpaux->aux.dev = &pdev->dev;
>
> - drm_dp_aux_init(&dpaux->aux);
> + err = drm_dp_aux_register_ddc(&dpaux->aux);
> + if (err < 0)
> + return err;
>
> /*
> * Assume that by default the DPAUX/I2C pads will be used for HDMI,
> @@ -585,6 +587,8 @@ static int tegra_dpaux_remove(struct platform_device *pdev)
> pm_runtime_put_sync(&pdev->dev);
> pm_runtime_disable(&pdev->dev);
>
> + drm_dp_aux_unregister_ddc(&dpaux->aux);
> +
> mutex_lock(&dpaux_lock);
> list_del(&dpaux->list);
> mutex_unlock(&dpaux_lock);
> @@ -718,7 +722,7 @@ int drm_dp_aux_attach(struct drm_dp_aux *aux, struct tegra_output *output)
> int err;
>
> aux->drm_dev = output->connector.dev;
> - err = drm_dp_aux_register(aux);
> + err = drm_dp_aux_register_chardev(aux);
> if (err < 0)
> return err;
>
> @@ -759,7 +763,7 @@ int drm_dp_aux_detach(struct drm_dp_aux *aux)
> unsigned long timeout;
> int err;
>
> - drm_dp_aux_unregister(aux);
> + drm_dp_aux_unregister_chardev(aux);
> disable_irq(dpaux->irq);
>
> if (dpaux->output->panel) {
> --
> 2.33.1
>

--
Daniel Vetter
Software Engineer, Intel Corporation