[PATCH 4/4] drm/sun4i: make sure we don't have a commit pending

Chen-Yu Tsai
2017-07-14T08:56:01Z

Hi,

On Thu, Jul 13, 2017 at 10:41 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> In the earlier display engine designs, any register access while a commit
> is pending is forbidden.
>
> One of the symptoms is that reading a register will return another, random,
> register value which can lead to register corruptions if we ever do a
> read/modify/write cycle.

Alternatively, if changes to the backend (layers) are guaranteed to happen
while the CRTC is disabled (which seems to be the case after looking at
drm_atomic_helper_commit_planes and drm_atomic_helper_commit_tail), we
could just turn on register auto-commit all the time and not deal with
this.

ChenYu

>
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
> drivers/gpu/drm/sun4i/sun4i_backend.c | 14 ++++++++++++++
> drivers/gpu/drm/sun4i/sun4i_crtc.c | 1 +
> 2 files changed, 15 insertions(+)
>
> diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c
> index cf480218daa5..ce1f40f7511e 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_backend.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c
> @@ -67,6 +67,19 @@ static void sun4i_backend_commit(struct sunxi_engine *engine)
> SUN4I_BACKEND_REGBUFFCTL_LOADCTL);
> }
>
> +static int sun4i_backend_commit_poll(struct sunxi_engine *engine)
> +{
> + u32 val;
> +
> + DRM_DEBUG_DRIVER("Polling for the commit to end\n");
> +
> + return regmap_read_poll_timeout(engine->regs,
> + SUN4I_BACKEND_REGBUFFCTL_REG,
> + val,
> + !(val & SUN4I_BACKEND_REGBUFFCTL_LOADCTL),
> + 100, 50000);
> +}
> +
> void sun4i_backend_layer_enable(struct sun4i_backend *backend,
> int layer, bool enable)
> {
> @@ -330,6 +343,7 @@ static int sun4i_backend_of_get_id(struct device_node *node)
>
> static const struct sunxi_engine_ops sun4i_backend_engine_ops = {
> .commit = sun4i_backend_commit,
> + .commit_poll = sun4i_backend_commit_poll,
> .layers_init = sun4i_layers_init,
> .apply_color_correction = sun4i_backend_apply_color_correction,
> .disable_color_correction = sun4i_backend_disable_color_correction,
> diff --git a/drivers/gpu/drm/sun4i/sun4i_crtc.c b/drivers/gpu/drm/sun4i/sun4i_crtc.c
> index 2eba1d8639d8..31550493fa1d 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_crtc.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_crtc.c
> @@ -34,6 +34,7 @@ static void sun4i_crtc_atomic_begin(struct drm_crtc *crtc,
> struct drm_crtc_state *old_state)
> {
> struct sun4i_crtc *scrtc = drm_crtc_to_sun4i_crtc(crtc);
> + struct sunxi_engine *engine = scrtc->engine;
> struct drm_device *dev = crtc->dev;
> unsigned long flags;
>
> --
> git-series 0.9.1