diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c index 613404f86668..84e3decb17b1 100644 --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c @@ -1040,10 +1040,41 @@ static bool vop_crtc_mode_fixup(struct drm_crtc *crtc, struct drm_display_mode *adjusted_mode) { struct vop *vop = to_vop(crtc); + unsigned long rate; - adjusted_mode->clock = - DIV_ROUND_UP(clk_round_rate(vop->dclk, - adjusted_mode->clock * 1000), 1000); + /* + * Clock craziness. + * + * Key points: + * + * - DRM works in in kHz. + * - Clock framework works in Hz. + * - Rockchip's clock driver picks the clock rate that is the + * same _OR LOWER_ than the one requested. + * + * Action plan: + * + * 1. When DRM gives us a mode, we should add 999 Hz to it. That way + * if the clock we need is 60000001 Hz (~60 MHz) and DRM tells us to + * make 60000 kHz then the clock framework will actually give us + * the right clock. + * + * NOTE: if the PLL (maybe through a divider) could actually make + * a clock rate 999 Hz higher instead of the one we want then this + * could be a problem. Unfortunately there's not much we can do + * since it's baked into DRM to use kHz. It shouldn't matter in + * practice since Rockchip PLLs are controlled by tables and + * even if there is a divider in the middle I wouldn't expect PLL + * rates in the table that are just a few kHz different. + * + * 2. Get the clock framework to round the rate for us to tell us + * what it will actually make. + * + * 3. Store the rounded up rate so that we don't need to worry about + * this in the actual clk_set_rate(). + */ + rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 + 999); + adjusted_mode->clock = DIV_ROUND_UP(rate, 1000); return true; }