[PATCH v2 10/12] drm/bridge: samsung-dsim: samsung_dsim_host_attach: use a temporary variable for the next bridge

[Marek Szyprowski]

On 09.01.2026 08:31, Luca Ceresoli wrote:
> In preparation to handle refcounting of the out_bridge, we need to ensure
> the out_bridge pointer contains either a valid bridge pointer or NULL, not
> an ERR_PTR. Otherwise calls such as drm_bridge_get/put() would try to
> redeference an ERR_PTR.
>
> As a preliminary cleanup, add a temporary local 'next_bridge' pointer and
> only copy it in dsi->out_bridge as late as possible, i.e. just before
> calling pdata->host_ops->attach() which uses it (only in the exynos
> driver).
>
> Not strictly needed, but for symmetry move the clearing of dsi->out_bridge
> in samsung_dsim_host_detach() to after pdata->host_ops->detach().
>
> Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>
Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>
> ---
>
> Changes in v2:
> - fix "pointer set too late" bug (NULL pointer deref in the exynos case)
> - *not* add Acked-by: Maxime as the patch has changed
> ---
>   drivers/gpu/drm/bridge/samsung-dsim.c | 26 +++++++++++++++++---------
>   1 file changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index eabc4c32f6ab..8dd058124e93 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1886,6 +1886,7 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
>   {
>   	struct samsung_dsim *dsi = host_to_dsi(host);
>   	const struct samsung_dsim_plat_data *pdata = dsi->plat_data;
> +	struct drm_bridge *next_bridge;
>   	struct device *dev = dsi->dev;
>   	struct device_node *np = dev->of_node;
>   	struct device_node *remote;
> @@ -1924,17 +1925,17 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
>   
>   	panel = of_drm_find_panel(remote);
>   	if (!IS_ERR(panel)) {
> -		dsi->out_bridge = devm_drm_panel_bridge_add(dev, panel);
> +		next_bridge = devm_drm_panel_bridge_add(dev, panel);
>   	} else {
> -		dsi->out_bridge = of_drm_find_bridge(remote);
> -		if (!dsi->out_bridge)
> -			dsi->out_bridge = ERR_PTR(-EINVAL);
> +		next_bridge = of_drm_find_bridge(remote);
> +		if (!next_bridge)
> +			next_bridge = ERR_PTR(-EINVAL);
>   	}
>   
>   	of_node_put(remote);
>   
> -	if (IS_ERR(dsi->out_bridge)) {
> -		ret = PTR_ERR(dsi->out_bridge);
> +	if (IS_ERR(next_bridge)) {
> +		ret = PTR_ERR(next_bridge);
>   		DRM_DEV_ERROR(dev, "failed to find the bridge: %d\n", ret);
>   		return ret;
>   	}
> @@ -1958,10 +1959,13 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
>   			return ret;
>   	}
>   
> +	// The next bridge can be used by host_ops->attach
> +	dsi->out_bridge = next_bridge;
> +
>   	if (pdata->host_ops && pdata->host_ops->attach) {
>   		ret = pdata->host_ops->attach(dsi, device);
>   		if (ret)
> -			return ret;
> +			goto err_release_next_bridge;
>   	}
>   
>   	dsi->lanes = device->lanes;
> @@ -1969,6 +1973,10 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
>   	dsi->mode_flags = device->mode_flags;
>   
>   	return 0;
> +
> +err_release_next_bridge:
> +	dsi->out_bridge = NULL;
> +	return ret;
>   }
>   
>   static void samsung_dsim_unregister_te_irq(struct samsung_dsim *dsi)
> @@ -1985,11 +1993,11 @@ static int samsung_dsim_host_detach(struct mipi_dsi_host *host,
>   	struct samsung_dsim *dsi = host_to_dsi(host);
>   	const struct samsung_dsim_plat_data *pdata = dsi->plat_data;
>   
> -	dsi->out_bridge = NULL;
> -
>   	if (pdata->host_ops && pdata->host_ops->detach)
>   		pdata->host_ops->detach(dsi, device);
>   
> +	dsi->out_bridge = NULL;
> +
>   	samsung_dsim_unregister_te_irq(dsi);
>   
>   	drm_bridge_remove(&dsi->bridge);
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland