Re: [PATCH v2 3/8] drm/bridge/synopsys: dsi: defer probing if panel not available in bridge-attach

Andrzej Hajda
2018-07-03T12:42:49Z

On 18.06.2018 12:28, Heiko Stuebner wrote:
> When the panel-driver is build as a module it currently fails hard as the
> panel cannot be probed directly:
>
> dw_mipi_dsi_bind()
> __dw_mipi_dsi_probe()
> creates dsi bus
> creates panel device
> triggers panel module load
> panel not probed (module not loaded or panel probe slow)
> drm_bridge_attach
> fails with -EINVAL due to empty panel_bridge
>
> So emit a -EPROBE_DEFER in that case to give the driver another
> chance at getting the display later.

Thats odd (at least for me), if the resource (panel in this case) is not
present, bridge should not be attached (drm_bridge_attach should not be
called). Ie __dw_mipi_dsi_probe should rather look for the panel and
defer if not found. Resource gathering is the task of probe.
drm_bridge_attach can be called after probe and it would be difficult
for the caller to react properly for -EPROBE_DEFER error.

Regards
Andrzej

>
> Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> ---
> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> index bb4aeca5c0f9..bd503f000ed5 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> @@ -835,6 +835,9 @@ static int dw_mipi_dsi_bridge_attach(struct drm_bridge *bridge)
> return -ENODEV;
> }
>
> + if (!dsi->panel_bridge)
> + return -EPROBE_DEFER;
> +
> /* Set the encoder type as caller does not know it */
> bridge->encoder->encoder_type = DRM_MODE_ENCODER_DSI;