Re: [PATCH] drm/nouveau: don't attempt to schedule hpd_work on headless cards

[Ben Skeggs <bskeggs@xxxxxxxxxx>]

On 29/5/24 07:52, Vasily Khoruzhick wrote:

> If the card doesn't have display hardware, hpd_work and hpd_lock are
> left uninitialized which causes BUG when attempting to schedule hpd_work
> on runtime PM resume.

Hi,

Good catch, thank you for looking at this.  A couple of initial comments 
below:

Ben.

> Fix it by adding headless flag to DRM and skip any hpd if it's set.
>
> Fixes: ae1aadb1eb8d ("nouveau: don't fail driver load if no display hw present.")
> Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/337
> Signed-off-by: Vasily Khoruzhick <anarsoul@xxxxxxxxx>
> ---
>   drivers/gpu/drm/nouveau/dispnv04/disp.c     |  2 +-
>   drivers/gpu/drm/nouveau/dispnv50/disp.c     |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_connector.c |  3 +++
>   drivers/gpu/drm/nouveau/nouveau_display.c   | 11 ++++++++++-
>   drivers/gpu/drm/nouveau/nouveau_drv.h       |  1 +
>   5 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/dispnv04/disp.c b/drivers/gpu/drm/nouveau/dispnv04/disp.c
> index 13705c5f1497..4b7497a8755c 100644
> --- a/drivers/gpu/drm/nouveau/dispnv04/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv04/disp.c
> @@ -68,7 +68,7 @@ nv04_display_fini(struct drm_device *dev, bool runtime, bool suspend)
>   	if (nv_two_heads(dev))
>   		NVWriteCRTC(dev, 1, NV_PCRTC_INTR_EN_0, 0);
>   
> -	if (!runtime)
> +	if (!runtime && !drm->headless)
>   		cancel_work_sync(&drm->hpd_work);
>   
>   	if (!suspend)
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index 88728a0b2c25..674dc567e179 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -2680,7 +2680,7 @@ nv50_display_fini(struct drm_device *dev, bool runtime, bool suspend)
>   			nv50_mstm_fini(nouveau_encoder(encoder));
>   	}
>   
> -	if (!runtime)
> +	if (!runtime && !drm->headless)
>   		cancel_work_sync(&drm->hpd_work);
>   }
>   
> diff --git a/drivers/gpu/drm/nouveau/nouveau_connector.c b/drivers/gpu/drm/nouveau/nouveau_connector.c
> index 856b3ef5edb8..b315a2ef5b28 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_connector.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_connector.c
> @@ -1190,6 +1190,9 @@ nouveau_connector_hpd(struct nouveau_connector *nv_connector, u64 bits)
>   	u32 mask = drm_connector_mask(&nv_connector->base);
>   	unsigned long flags;
>   
> +	if (drm->headless)
> +		return;
> +

You shouldn't need this change, the function can't be called if there's 
no display.


>   	spin_lock_irqsave(&drm->hpd_lock, flags);
>   	if (!(drm->hpd_pending & mask)) {
>   		nv_connector->hpd_pending |= bits;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
> index aed5d5b51b43..1961ef665e97 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_display.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_display.c
> @@ -450,6 +450,9 @@ nouveau_display_hpd_resume(struct drm_device *dev)
>   {
>   	struct nouveau_drm *drm = nouveau_drm(dev);
>   
> +	if (drm->headless)
> +		return;
> +
>   	spin_lock_irq(&drm->hpd_lock);
>   	drm->hpd_pending = ~0;
>   	spin_unlock_irq(&drm->hpd_lock);
> @@ -468,6 +471,11 @@ nouveau_display_hpd_work(struct work_struct *work)
>   	int changed = 0;
>   	struct drm_connector *first_changed_connector = NULL;
>   
> +	WARN_ON_ONCE(drm->headless);
> +
> +	if (drm->headless)
> +		return;
> +

Same here.


>   	pm_runtime_get_sync(dev->dev);
>   
>   	spin_lock_irq(&drm->hpd_lock);
> @@ -635,7 +643,7 @@ nouveau_display_fini(struct drm_device *dev, bool suspend, bool runtime)
>   	}
>   	drm_connector_list_iter_end(&conn_iter);
>   
> -	if (!runtime)
> +	if (!runtime && !drm->headless)
>   		cancel_work_sync(&drm->hpd_work);
>   
>   	drm_kms_helper_poll_disable(dev);
> @@ -729,6 +737,7 @@ nouveau_display_create(struct drm_device *dev)
>   		/* no display hw */
>   		if (ret == -ENODEV) {
>   			ret = 0;
> +			drm->headless = true;
>   			goto disp_create_err;
>   		}
>   
> diff --git a/drivers/gpu/drm/nouveau/nouveau_drv.h b/drivers/gpu/drm/nouveau/nouveau_drv.h
> index e239c6bf4afa..25fca98a20bc 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_drv.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_drv.h
> @@ -276,6 +276,7 @@ struct nouveau_drm {
>   	/* modesetting */
>   	struct nvbios vbios;
>   	struct nouveau_display *display;
> +	bool headless;
>   	struct work_struct hpd_work;
>   	spinlock_t hpd_lock;
>   	u32 hpd_pending;