Re: [PATCH v3 1/4] drm/mxsfb: Fix initial corrupt frame when activating display

[Stefan Agner <stefan@agner.ch>]

On 06.08.2018 21:31, Leonard Crestez wrote:
> LCDIF will repeatedly display data from CUR_BUF and set CUR_BUF to
> NEXT_BUF when done. Since we are only ever writing to NEXT_BUF the
> display will show an initial corrupt frame.
> 
> Fix by writing the FB paddr to both CUR_BUF and NEXT_BUF when
> activating the CRTC.

Really like how this patch set evolves! Only some minor thing below...

> 
> Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
> ---
>  drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 42 +++++++++++++++++++++---------
>  1 file changed, 29 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> index 0abe77675b76..db3ff5bde122 100644
> --- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> +++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
> @@ -194,15 +194,31 @@ static int mxsfb_reset_block(void __iomem *reset_addr)
>  		return ret;
>  
>  	return clear_poll_bit(reset_addr, MODULE_CLKGATE);
>  }
>  
> +static dma_addr_t mxsfb_get_fb_paddr(struct mxsfb_drm_private *mxsfb)
> +{
> +	struct drm_framebuffer *fb = mxsfb->pipe.plane.state->fb;
> +	struct drm_gem_cma_object *gem;
> +
> +	if (!fb)
> +		return 0;
> +
> +	gem = drm_fb_cma_get_gem_obj(fb, 0);
> +	if (!gem)
> +		return 0;
> +
> +	return gem->paddr;
> +}
> +
>  static void mxsfb_crtc_mode_set_nofb(struct mxsfb_drm_private *mxsfb)
>  {
>  	struct drm_display_mode *m = &mxsfb->pipe.crtc.state->adjusted_mode;
>  	const u32 bus_flags = mxsfb->connector.display_info.bus_flags;
>  	u32 vdctrl0, vsync_pulse_len, hsync_pulse_len;
> +	dma_addr_t paddr;
>  	int err;
>  
>  	/*
>  	 * It seems, you can't re-program the controller if it is still
>  	 * running. This may lead to shifted pictures (FIFO issue?), so
> @@ -268,10 +284,16 @@ static void mxsfb_crtc_mode_set_nofb(struct
> mxsfb_drm_private *mxsfb)
>  	       mxsfb->base + LCDC_VDCTRL3);
>  
>  	writel(SET_DOTCLK_H_VALID_DATA_CNT(m->hdisplay),
>  	       mxsfb->base + LCDC_VDCTRL4);
>  
> +	/* Update cur_buf as well to avoid an initial corrupt frame */
> +	paddr = mxsfb_get_fb_paddr(mxsfb);
> +	if (paddr) {
> +		writel(paddr, mxsfb->base + mxsfb->devdata->cur_buf);
> +		writel(paddr, mxsfb->base + mxsfb->devdata->next_buf);
> +	}

Traditionally mxsfb_crtc_mode_set_nofb() was used as a callback to
mode_set_nofb. And that callback should not fiddle with the fb (as the
name says).

So I rather prefer to move the new bits to mxsfb_crtc_enable(), between
mxsfb_crtc_mode_set_nofb() and mxsfb_enable_controller(). It is only
cosmetics, but I'd rather prefer to have it in the right place.

Currently the AXI clock is disabled between those functions... I suggest
to enable the AXI clock once in mxsfb_crtc_enable(). This puts an end to
the unnecessary enable/disable/enable sequence in mxsfb_crtc_enable().

So I suggest to create a patch "drm/mxsfb: simplify AXI clock handling"

--- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
@@ -129,7 +129,6 @@ static void mxsfb_enable_controller(struct
mxsfb_drm_private *mxsfb)
        if (mxsfb->clk_disp_axi)
                clk_prepare_enable(mxsfb->clk_disp_axi);
        clk_prepare_enable(mxsfb->clk);
-       mxsfb_enable_axi_clk(mxsfb);
 
        /* If it was disabled, re-enable the mode again */
        writel(CTRL_DOTCLK_MODE, mxsfb->base + LCDC_CTRL + REG_SET);
@@ -159,8 +158,6 @@ static void mxsfb_disable_controller(struct
mxsfb_drm_private *mxsfb)
        reg &= ~VDCTRL4_SYNC_SIGNALS_ON;
        writel(reg, mxsfb->base + LCDC_VDCTRL4);
 
-       mxsfb_disable_axi_clk(mxsfb);
-
        clk_disable_unprepare(mxsfb->clk);
        if (mxsfb->clk_disp_axi)
                clk_disable_unprepare(mxsfb->clk_disp_axi);
@@ -208,7 +205,6 @@ static void mxsfb_crtc_mode_set_nofb(struct
mxsfb_drm_private *mxsfb)
         * running. This may lead to shifted pictures (FIFO issue?), so
         * first stop the controller and drain its FIFOs.
         */
-       mxsfb_enable_axi_clk(mxsfb);
 
        /* Mandatory eLCDIF reset as per the Reference Manual */
        err = mxsfb_reset_block(mxsfb->base);
@@ -269,12 +265,11 @@ static void mxsfb_crtc_mode_set_nofb(struct
mxsfb_drm_private *mxsfb)
 
        writel(SET_DOTCLK_H_VALID_DATA_CNT(m->hdisplay),
               mxsfb->base + LCDC_VDCTRL4);
-
-       mxsfb_disable_axi_clk(mxsfb);
 }
 
 void mxsfb_crtc_enable(struct mxsfb_drm_private *mxsfb)
 {
+       mxsfb_enable_axi_clk(mxsfb);
        mxsfb_crtc_mode_set_nofb(mxsfb);
        mxsfb_enable_controller(mxsfb);
 }
@@ -282,6 +277,7 @@ void mxsfb_crtc_enable(struct mxsfb_drm_private
*mxsfb)
 void mxsfb_crtc_disable(struct mxsfb_drm_private *mxsfb)
 {
        mxsfb_disable_controller(mxsfb);
+       mxsfb_disable_axi_clk(mxsfb);
 }
 

Then move the above section between mxsfb_crtc_mode_set_nofb() and
mxsfb_enable_controller().

--
Stefan

>  	mxsfb_disable_axi_clk(mxsfb);
>  }
>  
>  void mxsfb_crtc_enable(struct mxsfb_drm_private *mxsfb)
>  {
> @@ -287,16 +309,12 @@ void mxsfb_crtc_disable(struct mxsfb_drm_private *mxsfb)
>  void mxsfb_plane_atomic_update(struct mxsfb_drm_private *mxsfb,
>  			       struct drm_plane_state *state)
>  {
>  	struct drm_simple_display_pipe *pipe = &mxsfb->pipe;
>  	struct drm_crtc *crtc = &pipe->crtc;
> -	struct drm_framebuffer *fb = pipe->plane.state->fb;
>  	struct drm_pending_vblank_event *event;
> -	struct drm_gem_cma_object *gem;
> -
> -	if (!crtc)
> -		return;
> +	dma_addr_t paddr;
>  
>  	spin_lock_irq(&crtc->dev->event_lock);
>  	event = crtc->state->event;
>  	if (event) {
>  		crtc->state->event = NULL;
> @@ -307,14 +325,12 @@ void mxsfb_plane_atomic_update(struct
> mxsfb_drm_private *mxsfb,
>  			drm_crtc_send_vblank_event(crtc, event);
>  		}
>  	}
>  	spin_unlock_irq(&crtc->dev->event_lock);
>  
> -	if (!fb)
> -		return;
> -
> -	gem = drm_fb_cma_get_gem_obj(fb, 0);
> -
> -	mxsfb_enable_axi_clk(mxsfb);
> -	writel(gem->paddr, mxsfb->base + mxsfb->devdata->next_buf);
> -	mxsfb_disable_axi_clk(mxsfb);
> +	paddr = mxsfb_get_fb_paddr(mxsfb);
> +	if (paddr) {
> +		mxsfb_enable_axi_clk(mxsfb);
> +		writel(paddr, mxsfb->base + mxsfb->devdata->next_buf);
> +		mxsfb_disable_axi_clk(mxsfb);
> +	}
>  }