On Wed, Dec 25, 2024 at 01:10:13AM +0200, Dmitry Baryshkov wrote:
> CEC adapter functions are protected by drm_dev_enter() / _exit(), so it
> is safe to keep CEC registered until DRM device is being torn down. Drop
> custom CEC unsregistration code and rely on the DRM core to unregister
> CEC adapter.
>
> Signed-off-by: Dmitry Baryshkov <dmitry.barysh...@linaro.org>
> ---
> drivers/gpu/drm/vc4/vc4_hdmi.c | 53
> ++++++------------------------------------
> 1 file changed, 7 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index
> 3086c2ad3bb2e8fafdc1f37ba985aa5785d49f9a..7b39000369e50f5368384575aa81919df5a7133c
> 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -2752,13 +2752,6 @@ static const struct cec_adap_ops vc4_hdmi_cec_adap_ops
> = {
> .adap_transmit = vc4_hdmi_cec_adap_transmit,
> };
>
> -static void vc4_hdmi_cec_release(void *ptr)
> -{
> - struct drm_connector *connector = ptr;
> -
> - drm_connector_cec_unregister(connector);
> -}
> -
> static int vc4_hdmi_cec_init(struct drm_connector *connector)
> {
> struct vc4_hdmi *vc4_hdmi = connector_to_vc4_hdmi(connector);
> @@ -2796,51 +2789,19 @@ static int vc4_hdmi_cec_register(struct vc4_hdmi
> *vc4_hdmi)
> {
> struct platform_device *pdev = vc4_hdmi->pdev;
> struct device *dev = &pdev->dev;
> - int ret;
>
> if (!of_property_present(dev->of_node, "interrupts")) {
> dev_warn(dev, "'interrupts' DT property is missing, no CEC\n");
> return 0;
> }
>
> - ret = drm_connector_hdmi_cec_adapter_register(&vc4_hdmi->connector,
> - &vc4_hdmi_cec_adap_ops,
> -
> vc4_hdmi->variant->card_name,
> - 1,
> - vc4_hdmi_cec_init,
> - NULL,
> - &pdev->dev);
> - if (ret < 0)
> - return ret;
> -
> - /*
> - * NOTE: Strictly speaking, we should probably use a DRM-managed
> - * registration there to avoid removing the CEC adapter by the
> - * time the DRM driver doesn't have any user anymore.
> - *
> - * However, the CEC framework already cleans up the CEC adapter
> - * only when the last user has closed its file descriptor, so we
> - * don't need to handle it in DRM.
> - *
> - * By the time the device-managed hook is executed, we will give
> - * up our reference to the CEC adapter and therefore don't
> - * really care when it's actually freed.
> - *
> - * There's still a problematic sequence: if we unregister our
> - * CEC adapter, but the userspace keeps a handle on the CEC
> - * adapter but not the DRM device for some reason. In such a
> - * case, our vc4_hdmi structure will be freed, but the
> - * cec_adapter structure will have a dangling pointer to what
> - * used to be our HDMI controller. If we get a CEC call at that
> - * moment, we could end up with a use-after-free. Fortunately,
> - * the CEC framework already handles this too, by calling
> - * cec_is_registered() in cec_ioctl() and cec_poll().
> - */I'd really like to keep that comment, somewhere. Maxime
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