Hi Linus,
Thank you for the patch.
On Friday, 15 December 2017 14:10:47 EET Linus Walleij wrote:
> If the bridge has a too strict setup time for the incoming
> signals, we may not be fast enough and then we need to
> compensate by outputting the signal on the inverse clock
> edge so it is for sure stable when the bridge samples it.
>
> Since bridges in difference to panels does not expose their
> connectors, make the connector optional in the display
> setup code.
>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> ChangeLog v4->v5:
> - Use the new bridge timings setup method.
> ---
> drivers/gpu/drm/pl111/Kconfig | 1 +
> drivers/gpu/drm/pl111/pl111_display.c | 35 ++++++++++++++++++++++++++++----
> drivers/gpu/drm/pl111/pl111_drv.c | 20 +++++++++++---------
> 3 files changed, 43 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/pl111/Kconfig b/drivers/gpu/drm/pl111/Kconfig
> index e5e2abd66491..82cb3e60ddc8 100644
> --- a/drivers/gpu/drm/pl111/Kconfig
> +++ b/drivers/gpu/drm/pl111/Kconfig
> @@ -8,6 +8,7 @@ config DRM_PL111
> select DRM_GEM_CMA_HELPER
> select DRM_BRIDGE
> select DRM_PANEL_BRIDGE
> + select DRM_DUMB_VGA_DAC
> select VT_HW_CONSOLE_BINDING if FRAMEBUFFER_CONSOLE
> help
> Choose this option for DRM support for the PL111 CLCD controller.
> diff --git a/drivers/gpu/drm/pl111/pl111_display.c
> b/drivers/gpu/drm/pl111/pl111_display.c index 06c4bf756b69..7fe4040aea46
> 100644
> --- a/drivers/gpu/drm/pl111/pl111_display.c
> +++ b/drivers/gpu/drm/pl111/pl111_display.c
> @@ -94,6 +94,7 @@ static void pl111_display_enable(struct
> drm_simple_display_pipe *pipe, const struct drm_display_mode *mode =
> &cstate->mode;
> struct drm_framebuffer *fb = plane->state->fb;
> struct drm_connector *connector = priv->connector;
> + struct drm_bridge *bridge = priv->bridge;
> u32 cntl;
> u32 ppl, hsw, hfp, hbp;
> u32 lpp, vsw, vfp, vbp;
> @@ -143,11 +144,37 @@ static void pl111_display_enable(struct
> drm_simple_display_pipe *pipe, if (mode->flags & DRM_MODE_FLAG_NVSYNC)
> tim2 |= TIM2_IVS;
>
> - if (connector->display_info.bus_flags & DRM_BUS_FLAG_DE_LOW)
> - tim2 |= TIM2_IOE;
> + if (connector) {
> + if (connector->display_info.bus_flags & DRM_BUS_FLAG_DE_LOW)
> + tim2 |= TIM2_IOE;
>
> - if (connector->display_info.bus_flags & DRM_BUS_FLAG_PIXDATA_NEGEDGE)
> - tim2 |= TIM2_IPC;
> + if (connector->display_info.bus_flags &
> + DRM_BUS_FLAG_PIXDATA_NEGEDGE)
> + tim2 |= TIM2_IPC;
> + }
> +
> + if (bridge) {
> + const struct drm_bridge_timings *btimings = bridge->timings;
> +
> + /*
> + * Here is when things get really fun. Sometimes the bridge
> + * timings are such that the signal out from PL11x is not
> + * stable before the receiving bridge (such as a dumb VGA DAC
> + * or similar) samples it. If that happens, we compensate by
> + * the only method we have: output the data on the opposite
> + * edge of the clock so it is for sure stable when it gets
> + * sampled.
> + *
> + * The PL111 manual does not contain proper timining diagrams
> + * or data for these details, but we know from experiments
> + * that the setup time is more than 3000 picoseconds (3 ns).
> + * If we have a bridge that requires the signal to be stable
> + * earlier than 3000 ps before the clock pulse, we have to
> + * output the data on the opposite edge to avoid flicker.
This should probably depend on the pixel clock frequency, but if it works for
you for now, I have no objection.
Acked-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> + */
> + if (btimings && btimings->setup_time_ps >= 3000)
> + tim2 ^= TIM2_IPC;
> + }
>
> tim2 |= cpl << 16;
> writel(tim2, priv->regs + CLCD_TIM2);
> diff --git a/drivers/gpu/drm/pl111/pl111_drv.c
> b/drivers/gpu/drm/pl111/pl111_drv.c index 201d57d5cb54..101a9c7db6ff 100644
> --- a/drivers/gpu/drm/pl111/pl111_drv.c
> +++ b/drivers/gpu/drm/pl111/pl111_drv.c
> @@ -107,11 +107,17 @@ static int pl111_modeset_init(struct drm_device *dev)
> ret = PTR_ERR(bridge);
> goto out_config;
> }
> - /*
> - * TODO: when we are using a different bridge than a panel
> - * (such as a dumb VGA connector) we need to devise a different
> - * method to get the connector out of the bridge.
> - */
> + } else if (bridge) {
> + dev_info(dev->dev, "Using non-panel bridge\n");
> + } else {
> + dev_err(dev->dev, "No bridge, exiting\n");
> + return -ENODEV;
> + }
> +
> + priv->bridge = bridge;
> + if (panel) {
> + priv->panel = panel;
> + priv->connector = panel->connector;
> }
>
> ret = pl111_display_init(dev);
> @@ -125,10 +131,6 @@ static int pl111_modeset_init(struct drm_device *dev)
> if (ret)
> return ret;
>
> - priv->bridge = bridge;
> - priv->panel = panel;
> - priv->connector = panel->connector;
> -
> ret = drm_vblank_init(dev, 1);
> if (ret != 0) {
> dev_err(dev->dev, "Failed to init vblank\n");
--
Regards,
Laurent Pinchart
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