Re: drm_bridges on fairphone-fp3 are enabled in the wrong order

[Doug Anderson]

Hi,

On Wed, Jul 5, 2023 at 12:51 AM Bert Karwatzki <spasswolf@xxxxxx> wrote:
>
> The fairphone-fp3 has a drm_panel attached to a dsi bridge. This are added to
> the bridge_chain in struct drm_encoder in the order dsi, panel. When the
> drm_atomic_bridge_chain_pre_enable these get enabled in the order panel, dsi
> because of the list_for_each_entry_reverse. But the drm_panel of the fairphone-
> fp3 is enabled using mipi_dsi_dcs_write_buffer which only works if the dsi is
> enabled before the panel.
>  To work around this one can revert
>
> commit 9e15123eca7942caa8a3e1f58ec0df7d088df149
> Author: Douglas Anderson <dianders@xxxxxxxxxxxx>
> Date:   Tue Jan 31 14:18:25 2023 -0800
>
>     drm/msm/dsi: Stop unconditionally powering up DSI hosts at modeset
>
> This leads to a working panel on startup. But when suspending one runs again
> into a similar problem. When the bridges are disabled the dsi is disabled first
> which leads to a failure in disabling the panel again because
> mipi_dsi_dcs_write_buffer fails when the dsi is already switched of.
>  As a simple workarund for both problems I have found it works to exchange the
> order of the bridge chain in drm_endcoder:
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index 28b8012a21f2..990f7c68a27c 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -550,6 +555,8 @@ int msm_dsi_manager_ext_bridge_init(u8 id)
>                 if (ret < 0)
>                         return ret;
>         }
> +       /* swap bridges in list */
> +       list_swap(&encoder->bridge_chain, encoder->bridge_chain.next);
>
>         /* The pipeline is ready, ping encoders if necessary */
>         msm_dsi_manager_set_split_display(id);
>
> But this does not look like a portable solution so I wonder if there is a better
> way to do this.
>
> The linux kernel used here is a linux-next-20220630, with several out-of-tree
> patches which are needed for the msm8953 gpu and the display used in the
> fairphone-fp3 located here: https://github.com/spasswolf/msm8953-linux.git in
> branch msm8953_iommu_rebase_v2_wlan_modem_ipa_cpufreq_display_debug.

Any chance that "pre_enable_prev_first" works for you? For the best
summary I'm aware of this issue, see:

https://lore.kernel.org/r/CAD=FV=X_xonf1Dz0BsNTKm4-zBm+ccKvPO+wEWFVMUVY_2=h3Q@xxxxxxxxxxxxxx

-Doug