Re: [PATCH v3 1/2] drm/rockchip: vop: clear DMA stop bit upon vblank on RK3066

Val Packett
2024-06-02T03:36:23Z

On Mon, May 27 2024 at 20:11:49 -03:00:00, Val Packett
<val@packett.cool> wrote:
> The RK3066 VOP sets a dma_stop bit when it's done scanning out a frame
> and needs the driver to acknowledge that by clearing the bit.
>
> So unless we clear it "between" frames, the RGB output only shows
> noise
> instead of the picture. vblank seems to be the most appropriate place
> to
> do it, since it indicates exactly that: that the hardware is done
> with the frame.
>
> This seems to be a redundant synchronization mechanism that was
> removed
> in later iterations of the VOP hardware block.
>
> Fixes: f4a6de8 ("drm: rockchip: vop: add rk3066 vop definitions")
> Cc: stable@vger.kernel.org
> Signed-off-by: Val Packett <val@packett.cool>
> ---
> drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 6 ++++++
> drivers/gpu/drm/rockchip/rockchip_drm_vop.h | 1 +
> drivers/gpu/drm/rockchip/rockchip_vop_reg.c | 1 +
> 3 files changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> index a13473b2d..2731fe2b2 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> @@ -1766,6 +1766,12 @@ static void vop_handle_vblank(struct vop *vop)
> }
> spin_unlock(&drm->event_lock);
>
> + if (VOP_HAS_REG(vop, common, dma_stop)) {
> + spin_lock(&vop->reg_lock);
> + VOP_REG_SET(vop, common, dma_stop, 0);
> + spin_unlock(&vop->reg_lock);
> + }
> +

Oops… so doing it here actually causes deadlocks, unless we also
change all other reg_lock usages to be spin_lock_irq/spin_unlock_irq.

Not sure if doing that or going back to v1 would be better.