linux-kernel - Re: [PATCH RESEND v9 2/6] drm/bridge: cadence: cdns-mhdp8546-core: Add mode_valid hook to drm_bridge

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Message-ID: <8c97c5e9-7705-4368-a3a9-45e209582c3f@ideasonboard.com>
Date: Fri, 21 Nov 2025 14:43:07 +0200
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Harikrishna Shenoy <h-shenoy@...com>
Cc: Laurent.pinchart@...asonboard.com, airlied@...il.com,
 andrzej.hajda@...el.com, andy.yan@...k-chips.com, aradhya.bhatia@...ux.dev,
 devarsht@...com, dianders@...omium.org, dri-devel@...ts.freedesktop.org,
 javierm@...hat.com, jernej.skrabec@...il.com, jonas@...boo.se,
 linux-kernel@...r.kernel.org, linux@...blig.org, luca.ceresoli@...tlin.com,
 lumag@...nel.org, lyude@...hat.com, maarten.lankhorst@...ux.intel.com,
 mordan@...ras.ru, mripard@...nel.org, neil.armstrong@...aro.org,
 rfoss@...nel.org, s-jain1@...com, simona@...ll.ch, tzimmermann@...e.de,
 u-kumar1@...com
Subject: Re: [PATCH RESEND v9 2/6] drm/bridge: cadence: cdns-mhdp8546-core:
 Add mode_valid hook to drm_bridge_funcs

Hi,

On 20/11/2025 14:14, Harikrishna Shenoy wrote:
> From: Jayesh Choudhary <j-choudhary@...com>
> 
> Add cdns_mhdp_bridge_mode_valid() to check if specific mode is valid for
> this bridge or not. In the legacy usecase with
> !DRM_BRIDGE_ATTACH_NO_CONNECTOR we were using the hook from
> drm_connector_helper_funcs but with DRM_BRIDGE_ATTACH_NO_CONNECTOR
> we need to have mode_valid() in drm_bridge_funcs.

This looks fine, but a fix should always explain what the issue is. What
is the behavior without this patch, if DRM_BRIDGE_ATTACH_NO_CONNECTOR is
set?

 Tomi

> Fixes: c932ced6b585 ("drm/tidss: Update encoder/bridge chain connect model")
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> Signed-off-by: Harikrishna Shenoy <h-shenoy@...com>
> ---
>  .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 20 +++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> index f3076e9cdabbe..7178a01e4d4d8 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> @@ -2162,6 +2162,25 @@ static const struct drm_edid *cdns_mhdp_bridge_edid_read(struct drm_bridge *brid
>  	return cdns_mhdp_edid_read(mhdp, connector);
>  }
>  
> +static enum drm_mode_status
> +cdns_mhdp_bridge_mode_valid(struct drm_bridge *bridge,
> +			    const struct drm_display_info *info,
> +			    const struct drm_display_mode *mode)
> +{
> +	struct cdns_mhdp_device *mhdp = bridge_to_mhdp(bridge);
> +
> +	mutex_lock(&mhdp->link_mutex);
> +
> +	if (!cdns_mhdp_bandwidth_ok(mhdp, mode, mhdp->link.num_lanes,
> +				    mhdp->link.rate)) {
> +		mutex_unlock(&mhdp->link_mutex);
> +		return MODE_CLOCK_HIGH;
> +	}
> +
> +	mutex_unlock(&mhdp->link_mutex);
> +	return MODE_OK;
> +}
> +
>  static const struct drm_bridge_funcs cdns_mhdp_bridge_funcs = {
>  	.atomic_enable = cdns_mhdp_atomic_enable,
>  	.atomic_disable = cdns_mhdp_atomic_disable,
> @@ -2176,6 +2195,7 @@ static const struct drm_bridge_funcs cdns_mhdp_bridge_funcs = {
>  	.edid_read = cdns_mhdp_bridge_edid_read,
>  	.hpd_enable = cdns_mhdp_bridge_hpd_enable,
>  	.hpd_disable = cdns_mhdp_bridge_hpd_disable,
> +	.mode_valid = cdns_mhdp_bridge_mode_valid,
>  };
>  
>  static bool cdns_mhdp_detect_hpd(struct cdns_mhdp_device *mhdp, bool *hpd_pulse)