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.

Signed-off-by: Leonard Crestez <leonard.cres...@nxp.com>
Tested-by: Philipp Zabel <p.za...@pengutronix.de>
---
 drivers/gpu/drm/mxsfb/mxsfb_crtc.c | 45 +++++++++++++++++++++---------
 1 file changed, 32 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c 
b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
index e4fcbb65b969..24b1f0c1432e 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
+++ b/drivers/gpu/drm/mxsfb/mxsfb_crtc.c
@@ -191,10 +191,25 @@ 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;
@@ -267,12 +282,22 @@ static void mxsfb_crtc_mode_set_nofb(struct 
mxsfb_drm_private *mxsfb)
               mxsfb->base + LCDC_VDCTRL4);
 }
 
 void mxsfb_crtc_enable(struct mxsfb_drm_private *mxsfb)
 {
+       dma_addr_t paddr;
+
        mxsfb_enable_axi_clk(mxsfb);
        mxsfb_crtc_mode_set_nofb(mxsfb);
+
+       /* Write 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);
+       }
+
        mxsfb_enable_controller(mxsfb);
 }
 
 void mxsfb_crtc_disable(struct mxsfb_drm_private *mxsfb)
 {
@@ -283,16 +308,12 @@ 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;
@@ -303,14 +324,12 @@ 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);
+       }
 }
-- 
2.17.1

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