Re: [PATCH v2] drm/meson: Fixes for drm_crtc_vblank_on/off support

[Neil Armstrong]

Hi Stable team,

On 22/11/2018 17:01, Neil Armstrong wrote:
> Since Linux 4.17, calls to drm_crtc_vblank_on/off are mandatory, and we get
> a warning when ctrc is disabled :
> " driver forgot to call drm_crtc_vblank_off()"
> 
> But, the vsync IRQ was not totally disabled due the transient hardware
> state and specific interrupt line, thus adding proper IRQ masking from
> the HHI system control registers.
> 
> The last change fixes a race condition introduced by calling the added
> drm_crtc_vblank_on/off when an HPD event occurs from the HDMI connector,
> triggering a WARN_ON() in the _atomic_begin() callback when the CRTC
> is disabled, thus also triggering a WARN_ON() in drm_vblank_put() :
> 
> WARNING: CPU: 0 PID: 1185 at drivers/gpu/drm/meson/meson_crtc.c:157 meson_crtc_atomic_begin+0x78/0x80
> [...]
> Call trace:
>   meson_crtc_atomic_begin+0x78/0x80
>   drm_atomic_helper_commit_planes+0x140/0x218
>   drm_atomic_helper_commit_tail+0x38/0x80
>   commit_tail+0x7c/0x80
>   drm_atomic_helper_commit+0xdc/0x150
>   drm_atomic_commit+0x54/0x60
>   restore_fbdev_mode_atomic+0x198/0x238
>   restore_fbdev_mode+0x6c/0x1c0
>   drm_fb_helper_restore_fbdev_mode_unlocked+0x7c/0xf0
>   drm_fb_helper_set_par+0x34/0x60
>   drm_fb_helper_hotplug_event.part.28+0xb8/0xc8
>   drm_fbdev_client_hotplug+0xa4/0xe0
>   drm_client_dev_hotplug+0x90/0xe0
>   drm_kms_helper_hotplug_event+0x3c/0x48
>   drm_helper_hpd_irq_event+0x134/0x168
>   dw_hdmi_top_thread_irq+0x3c/0x50
> [...]
> WARNING: CPU: 0 PID: 1185 at drivers/gpu/drm/drm_vblank.c:1026 drm_vblank_put+0xb4/0xc8
> [...]
>  Call trace:
>   drm_vblank_put+0xb4/0xc8
>   drm_crtc_vblank_put+0x24/0x30
>   drm_atomic_helper_wait_for_vblanks.part.9+0x130/0x2b8
>   drm_atomic_helper_commit_tail+0x68/0x80
> [...]
> 
> The issue is that vblank need to be enabled in any occurence of :
> - atomic_enable()
> - atomic_begin() and state->enable == true, which was not the case
> 
> Moving the CRTC enable code to a common function and calling in one
> of these occurence solves this race condition and makes sure vblank
> is enabled in each call to _atomic_begin() from the HPD event leading
> to drm_atomic_helper_commit_planes().
> 
> To Summarize :
> - Make sure that the CRTC code will call the drm_crtc_vblank_on()/off()
> - *Really* mask the Vsync IRQ
> - Initialize and enable vblank at the first _atomic_begin()/_atomic_enable()

This fix hit linux master as commit id 2bcd3ecab773f73211c45bb1430bb52ac641f271
Coult it be applied on the Linux 4.19 stable tree ?

Thanks,
Neil

> 
> Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/meson/meson_crtc.c | 27 +++++++++++++++++++++++++--
>  drivers/gpu/drm/meson/meson_venc.c |  3 +++
>  2 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/meson/meson_crtc.c b/drivers/gpu/drm/meson/meson_crtc.c
> index d78168f979db..75d97f1b2e8f 100644
> --- a/drivers/gpu/drm/meson/meson_crtc.c
> +++ b/drivers/gpu/drm/meson/meson_crtc.c
> @@ -46,6 +46,7 @@ struct meson_crtc {
>  	struct drm_crtc base;
>  	struct drm_pending_vblank_event *event;
>  	struct meson_drm *priv;
> +	bool enabled;
>  };
>  #define to_meson_crtc(x) container_of(x, struct meson_crtc, base)
>  
> @@ -81,8 +82,7 @@ static const struct drm_crtc_funcs meson_crtc_funcs = {
>  
>  };
>  
> -static void meson_crtc_atomic_enable(struct drm_crtc *crtc,
> -				     struct drm_crtc_state *old_state)
> +static void meson_crtc_enable(struct drm_crtc *crtc)
>  {
>  	struct meson_crtc *meson_crtc = to_meson_crtc(crtc);
>  	struct drm_crtc_state *crtc_state = crtc->state;
> @@ -106,6 +106,22 @@ static void meson_crtc_atomic_enable(struct drm_crtc *crtc,
>  	writel_bits_relaxed(VPP_POSTBLEND_ENABLE, VPP_POSTBLEND_ENABLE,
>  			    priv->io_base + _REG(VPP_MISC));
>  
> +	drm_crtc_vblank_on(crtc);
> +
> +	meson_crtc->enabled = true;
> +}
> +
> +static void meson_crtc_atomic_enable(struct drm_crtc *crtc,
> +				     struct drm_crtc_state *old_state)
> +{
> +	struct meson_crtc *meson_crtc = to_meson_crtc(crtc);
> +	struct meson_drm *priv = meson_crtc->priv;
> +
> +	DRM_DEBUG_DRIVER("\n");
> +
> +	if (!meson_crtc->enabled)
> +		meson_crtc_enable(crtc);
> +
>  	priv->viu.osd1_enabled = true;
>  }
>  
> @@ -117,6 +133,8 @@ static void meson_crtc_atomic_disable(struct drm_crtc *crtc,
>  
>  	DRM_DEBUG_DRIVER("\n");
>  
> +	drm_crtc_vblank_off(crtc);
> +
>  	priv->viu.osd1_enabled = false;
>  	priv->viu.osd1_commit = false;
>  
> @@ -135,6 +153,8 @@ static void meson_crtc_atomic_disable(struct drm_crtc *crtc,
>  
>  		crtc->state->event = NULL;
>  	}
> +
> +	meson_crtc->enabled = false;
>  }
>  
>  static void meson_crtc_atomic_begin(struct drm_crtc *crtc,
> @@ -143,6 +163,9 @@ static void meson_crtc_atomic_begin(struct drm_crtc *crtc,
>  	struct meson_crtc *meson_crtc = to_meson_crtc(crtc);
>  	unsigned long flags;
>  
> +	if (crtc->state->enable && !meson_crtc->enabled)
> +		meson_crtc_enable(crtc);
> +
>  	if (crtc->state->event) {
>  		WARN_ON(drm_crtc_vblank_get(crtc) != 0);
>  
> diff --git a/drivers/gpu/drm/meson/meson_venc.c b/drivers/gpu/drm/meson/meson_venc.c
> index 9be0376e0329..ab72ddda242d 100644
> --- a/drivers/gpu/drm/meson/meson_venc.c
> +++ b/drivers/gpu/drm/meson/meson_venc.c
> @@ -71,6 +71,7 @@
>   */
>  
>  /* HHI Registers */
> +#define HHI_GCLK_MPEG2		0x148 /* 0x52 offset in data sheet */
>  #define HHI_VDAC_CNTL0		0x2F4 /* 0xbd offset in data sheet */
>  #define HHI_VDAC_CNTL1		0x2F8 /* 0xbe offset in data sheet */
>  #define HHI_HDMI_PHY_CNTL0	0x3a0 /* 0xe8 offset in data sheet */
> @@ -1663,10 +1664,12 @@ unsigned int meson_venci_get_field(struct meson_drm *priv)
>  void meson_venc_enable_vsync(struct meson_drm *priv)
>  {
>  	writel_relaxed(2, priv->io_base + _REG(VENC_INTCTRL));
> +	regmap_update_bits(priv->hhi, HHI_GCLK_MPEG2, BIT(25), BIT(25));
>  }
>  
>  void meson_venc_disable_vsync(struct meson_drm *priv)
>  {
> +	regmap_update_bits(priv->hhi, HHI_GCLK_MPEG2, BIT(25), 0);
>  	writel_relaxed(0, priv->io_base + _REG(VENC_INTCTRL));
>  }
>  
>