Re: [PATCH v4] drm/bridge: ti-sn65dsi86: Add HPD for DisplayPort connector type

[Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>]

Hi,

On 11/06/2025 08:29, Jayesh Choudhary wrote:
> By default, HPD was disabled on SN65DSI86 bridge. When the driver was
> added (commit "a095f15c00e27"), the HPD_DISABLE bit was set in pre-enable
> call which was moved to other function calls subsequently.
> Later on, commit "c312b0df3b13" added detect utility for DP mode. But with
> HPD_DISABLE bit set, all the HPD events are disabled[0] and the debounced
> state always return 1 (always connected state).
> 
> Set HPD_DISABLE bit conditionally based on connector type.
> Since the HPD_STATE is reflected correctly only after waiting for debounce
> time (~100-400ms) and adding this delay in detect() is not feasible
> owing to the performace impact (glitches and frame drop), remove runtime
> calls in detect() and add hpd_enable()/disable() bridge hooks with runtime
> calls, to detect hpd properly without any delay.
> 
> [0]: <https://www.ti.com/lit/gpn/SN65DSI86> (Pg. 32)
> 
> Fixes: c312b0df3b13 ("drm/bridge: ti-sn65dsi86: Implement bridge connector operations for DP")
> Cc: Max Krummenacher <max.krummenacher@toradex.com>
> Signed-off-by: Jayesh Choudhary <j-choudhary@ti.com>
> ---
> 
> Changelog v3->v4:
> - Remove "no-hpd" support due to backward compatibility issues
> - Change the conditional from "no-hpd" back to connector type
>   but still address [1]
> 
> v3 patch link:
> <https://lore.kernel.org/all/20250529110418.481756-1-j-choudhary@ti.com/>
> 
> Changelog v2->v3:
> - Change conditional based on no-hpd property to address [1]
> - Remove runtime calls in detect() with appropriate comments
> - Add hpd_enable() and hpd_disable() in drm_bridge_funcs
> 
> v2 patch link:
> <https://lore.kernel.org/all/20250508115433.449102-1-j-choudhary@ti.com/>
> 
> Changelog v1->v2:
> - Drop additional property in bindings and use conditional.
> - Instead of register read for HPD state, use dpcd read which returns 0
>   for success and error codes for no connection
> - Add relevant history for the required change in commit message
> - Drop RFC subject-prefix in v2
> - Add "Cc:" tag
> 
> v1 patch link:
> <https://lore.kernel.org/all/20250424105432.255309-1-j-choudhary@ti.com/>
> 
> [1]: <https://lore.kernel.org/all/mwh35anw57d6nvre3sguetzq3miu4kd43rokegvul7fk266lys@5h2euthpk7vq/>
> 
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 49 ++++++++++++++++++++++-----
>  1 file changed, 41 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 60224f476e1d..b674a1aa1a37 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -348,12 +348,20 @@ static void ti_sn65dsi86_enable_comms(struct ti_sn65dsi86 *pdata,
>  	 * 200 ms.  We'll assume that the panel driver will have the hardcoded
>  	 * delay in its prepare and always disable HPD.
>  	 *
> -	 * If HPD somehow makes sense on some future panel we'll have to
> -	 * change this to be conditional on someone specifying that HPD should
> -	 * be used.
> +	 * For DisplayPort connector type, now that HPD makes sense and is

This comment also is written like a commit description ("now that HPD
makes sense").

> +	 * required, use the connector type to conditionally disable HPD.
> +	 *
> +	 * NOTE: The bridge type is set in auxiliary_bridge probe but
> +	 * enable_comms() can be called before. So for DisplayPort,
> +	 * HPD will be enabled once bridge type is set.
> +	 * "no-hpd" property is not used properly in devicetree description
> +	 * and hence is unreliable. Therefore HPD is being enabled using
> +	 * this conditional.
>  	 */
> -	regmap_update_bits(pdata->regmap, SN_HPD_DISABLE_REG, HPD_DISABLE,
> -			   HPD_DISABLE);
> +
> +	if (pdata->bridge.type != DRM_MODE_CONNECTOR_DisplayPort)
> +		regmap_update_bits(pdata->regmap, SN_HPD_DISABLE_REG, HPD_DISABLE,
> +				   HPD_DISABLE);
>  
>  	pdata->comms_enabled = true;
>  
> @@ -1195,9 +1203,17 @@ static enum drm_connector_status ti_sn_bridge_detect(struct drm_bridge *bridge)
>  	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
>  	int val = 0;
>  
> -	pm_runtime_get_sync(pdata->dev);
> +	/*
> +	 * The chip won't report HPD right after being powered on as
> +	 * HPD_DEBOUNCED_STATE reflects correct state only after the
> +	 * debounce time (~100-400 ms).
> +	 * So having pm_runtime_get_sync() and immediately reading
> +	 * the register in detect() won't work, and adding delay()
> +	 * in detect will have performace impact in display.
> +	 * So remove runtime calls here.
> +	 */
> +

As Doug mentioned, the style here is more like a commit message. But
also, in my opinion, it would make more sense to have the comment in
hpd_enable() rather than having it here, mentioning that the chip needs
to be powered to have a reliable HPD due to the long debounce time.

>  	regmap_read(pdata->regmap, SN_HPD_DISABLE_REG, &val);
> -	pm_runtime_put_autosuspend(pdata->dev);
>  
>  	return val & HPD_DEBOUNCED_STATE ? connector_status_connected
>  					 : connector_status_disconnected;
> @@ -1220,6 +1236,20 @@ static void ti_sn65dsi86_debugfs_init(struct drm_bridge *bridge, struct dentry *
>  	debugfs_create_file("status", 0600, debugfs, pdata, &status_fops);
>  }
>  
> +static void ti_sn_bridge_hpd_enable(struct drm_bridge *bridge)
> +{
> +	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
> +
> +	pm_runtime_get_sync(pdata->dev);
> +}
> +
> +static void ti_sn_bridge_hpd_disable(struct drm_bridge *bridge)
> +{
> +	struct ti_sn65dsi86 *pdata = bridge_to_ti_sn65dsi86(bridge);
> +
> +	pm_runtime_put_sync(pdata->dev);

No need for _sync, afaics. Why not pm_runtime_put_autosuspend()?

 Tomi

> +}
> +
>  static const struct drm_bridge_funcs ti_sn_bridge_funcs = {
>  	.attach = ti_sn_bridge_attach,
>  	.detach = ti_sn_bridge_detach,
> @@ -1234,6 +1264,8 @@ static const struct drm_bridge_funcs ti_sn_bridge_funcs = {
>  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
>  	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
>  	.debugfs_init = ti_sn65dsi86_debugfs_init,
> +	.hpd_enable = ti_sn_bridge_hpd_enable,
> +	.hpd_disable = ti_sn_bridge_hpd_disable,
>  };
>  
>  static void ti_sn_bridge_parse_lanes(struct ti_sn65dsi86 *pdata,
> @@ -1322,7 +1354,8 @@ static int ti_sn_bridge_probe(struct auxiliary_device *adev,
>  			   ? DRM_MODE_CONNECTOR_DisplayPort : DRM_MODE_CONNECTOR_eDP;
>  
>  	if (pdata->bridge.type == DRM_MODE_CONNECTOR_DisplayPort)
> -		pdata->bridge.ops = DRM_BRIDGE_OP_EDID | DRM_BRIDGE_OP_DETECT;
> +		pdata->bridge.ops = DRM_BRIDGE_OP_EDID | DRM_BRIDGE_OP_DETECT |
> +				    DRM_BRIDGE_OP_HPD;
>  
>  	drm_bridge_add(&pdata->bridge);
>