linux-kernel - Re: [PATCH v2] drm/bridge:anx7625: Update HDCP status at atomic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <fy6zvkdidz2srerfq5bshgcshps2wfa4syxwndwesgxcej66ws@nf5svlpkeodh>
Date: Tue, 10 Dec 2024 03:08:17 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Xin Ji <xji@...logixsemi.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, bliang@...logixsemi.com, 
	qwen@...logixsemi.com, treapking@...gle.com, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge:anx7625: Update HDCP status at
 atomic_disable()

On Mon, Dec 09, 2024 at 02:46:32PM +0800, Xin Ji wrote:
> When user enabled HDCP feature, upper layer will set HDCP content
> to DRM_MODE_CONTENT_PROTECTION_DESIRED. Next, anx7625 will update
> HDCP content to DRM_MODE_CONTENT_PROTECTION_ENABLED if down stream
> support HDCP feature.
> 
> However once HDCP content turn to  DRM_MODE_CONTENT_PROTECTION_ENABLED
> upper layer will not update the HDCP content to
> DRM_MODE_CONTENT_PROTECTION_UNDESIRED until monitor disconnect.

What is "upper layer"? Is it a kernel or a userspace?

>From drm_hdcp_update_content_protection() documentation:

No uevent for DESIRED->UNDESIRED or ENABLED->UNDESIRED,
as userspace is triggering such state change and kernel performs it without
fail.This function update the new state of the property into the connector's
state and generate an uevent to notify the userspace.


> 
> So when user dynamic change the display resolution, anx7625 driver must
> call drm_hdcp_update_content_protection() to update HDCP content to
> DRM_MODE_CONTENT_PROTECTION_UNDESIRED in bridge interface
> .atomic_disable().

Why?

> 
> Signed-off-by: Xin Ji <xji@...logixsemi.com>
> ---
>  drivers/gpu/drm/bridge/analogix/anx7625.c | 25 ++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
> index a2675b121fe4..a75f519ddcb8 100644
> --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
> +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
> @@ -861,6 +861,22 @@ static int anx7625_hdcp_disable(struct anx7625_data *ctx)
>  				 TX_HDCP_CTRL0, ~HARD_AUTH_EN & 0xFF);
>  }
>  
> +static void anx7625_hdcp_disable_and_update_cp(struct anx7625_data *ctx)
> +{
> +	struct device *dev = ctx->dev;
> +
> +	if (!ctx->connector)
> +		return;
> +
> +	anx7625_hdcp_disable(ctx);
> +
> +	ctx->hdcp_cp = DRM_MODE_CONTENT_PROTECTION_UNDESIRED;
> +	drm_hdcp_update_content_protection(ctx->connector,
> +					   ctx->hdcp_cp);
> +
> +	dev_dbg(dev, "update CP to UNDESIRE\n");
> +}
> +
>  static int anx7625_hdcp_enable(struct anx7625_data *ctx)
>  {
>  	u8 bcap;
> @@ -2165,11 +2181,8 @@ static int anx7625_connector_atomic_check(struct anx7625_data *ctx,
>  			dev_err(dev, "current CP is not ENABLED\n");
>  			return -EINVAL;
>  		}
> -		anx7625_hdcp_disable(ctx);
> -		ctx->hdcp_cp = DRM_MODE_CONTENT_PROTECTION_UNDESIRED;
> -		drm_hdcp_update_content_protection(ctx->connector,
> -						   ctx->hdcp_cp);
> -		dev_dbg(dev, "update CP to UNDESIRE\n");
> +
> +		anx7625_hdcp_disable_and_update_cp(ctx);

No. atomic_check() MAY NOT perform any changes to the hardware. It might
be just a probe from userspace to check if the mode or a particular
option can be set in a particular way. There is no guarantee that
userspace will even try to commit it.

>  	}
>  
>  	if (cp == DRM_MODE_CONTENT_PROTECTION_ENABLED) {
> @@ -2449,6 +2462,8 @@ static void anx7625_bridge_atomic_disable(struct drm_bridge *bridge,
>  
>  	dev_dbg(dev, "drm atomic disable\n");
>  
> +	anx7625_hdcp_disable_and_update_cp(ctx);
> +
>  	ctx->connector = NULL;
>  	anx7625_dp_stop(ctx);
>  
> -- 
> 2.25.1
> 

-- 
With best wishes
Dmitry