diff --git a/drivers/gpu/drm/mxsfb/mxsfb_kms.c b/drivers/gpu/drm/mxsfb/mxsfb_kms.c index 300e7bab0f431..01e0f525360f6 100644 --- a/drivers/gpu/drm/mxsfb/mxsfb_kms.c +++ b/drivers/gpu/drm/mxsfb/mxsfb_kms.c @@ -115,6 +115,35 @@ static void mxsfb_enable_controller(struct mxsfb_drm_private *mxsfb) reg |= VDCTRL4_SYNC_SIGNALS_ON; writel(reg, mxsfb->base + LCDC_VDCTRL4); + /* + * Enable recovery on underflow. + * + * There is some sort of corner case behavior of the controller, + * which could rarely be triggered at least on i.MX6SX connected + * to 800x480 DPI panel and i.MX8MM connected to DPI->DSI->LVDS + * bridged 1920x1080 panel (and likely on other setups too), where + * the image on the panel shifts to the right and wraps around. + * This happens either when the controller is enabled on boot or + * even later during run time. The condition does not correct + * itself automatically, i.e. the display image remains shifted. + * + * It seems this problem is known and is due to sporadic underflows + * of the LCDIF FIFO. While the LCDIF IP does have underflow/overflow + * IRQs, neither of the IRQs trigger and neither IRQ status bit is + * asserted when this condition occurs. + * + * All known revisions of the LCDIF IP have CTRL1 RECOVER_ON_UNDERFLOW + * bit, which is described in the reference manual since i.MX23 as + * " + * Set this bit to enable the LCDIF block to recover in the next + * field/frame if there was an underflow in the current field/frame. + * " + * Enable this bit to mitigate the sporadic underflows. + */ + reg = readl(mxsfb->base + LCDC_CTRL1); + reg |= CTRL1_RECOVER_ON_UNDERFLOW; + writel(reg, mxsfb->base + LCDC_CTRL1); + writel(CTRL_RUN, mxsfb->base + LCDC_CTRL + REG_SET); } diff --git a/drivers/gpu/drm/mxsfb/mxsfb_regs.h b/drivers/gpu/drm/mxsfb/mxsfb_regs.h index 55d28a27f9124..df90e960f495c 100644 --- a/drivers/gpu/drm/mxsfb/mxsfb_regs.h +++ b/drivers/gpu/drm/mxsfb/mxsfb_regs.h @@ -54,6 +54,7 @@ #define CTRL_DF24 BIT(1) #define CTRL_RUN BIT(0) +#define CTRL1_RECOVER_ON_UNDERFLOW BIT(24) #define CTRL1_FIFO_CLEAR BIT(21) #define CTRL1_SET_BYTE_PACKAGING(x) (((x) & 0xf) << 16) #define CTRL1_GET_BYTE_PACKAGING(x) (((x) >> 16) & 0xf)