Re: [PATCH] drm: dw-hdmi: Implement the mode_fixup drm helper

[Archit Taneja <architt@codeaurora.org>]

Hi,

On 4/7/2017 5:47 PM, Romain Perier wrote:
> This helper is supposed to validate or reject the modeline before it
> applied by the mode setting. Currently this function has been dropped,
> it was previously set to a dummy function that always returned true. For
> both cases, this means that userspace can ask for a bad modeline that
> will be always accepted.
>
> On some platforms, like Rockchip, the drm dw_hdmi-rockchip variant driver
> already implements the atomic_check drm helper, so mode_fixup cannot be
> handled and implemented there (as drm_atomic_helper relies on either
> atomic_check or mode_fixup).
>
> This commit implements this helper. It only checks that this mode is
> correct from the connector point of view

We do have a atomic_check op in drm_connector_helper_funcs. I've
rarely seen it being used, but it could be used to validate
the mode w.r.t the connector, rather than checking it in the
bridge's mode_fixup op.

Daniel,

Is it okay to use the connector's atomic_check to validate a mode.
(by peeping into the new_crtc_state->mode?)

Thanks,
Archit

>
> Signed-off-by: Romain Perier <romain.perier@collabora.com>
> ---
>  drivers/gpu/drm/bridge/dw-hdmi.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/drivers/gpu/drm/bridge/dw-hdmi.c b/drivers/gpu/drm/bridge/dw-hdmi.c
> index 22211ff..3bd0807 100644
> --- a/drivers/gpu/drm/bridge/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/dw-hdmi.c
> @@ -1740,6 +1740,21 @@ static int dw_hdmi_bridge_attach(struct drm_bridge *bridge)
>  	return 0;
>  }
>
> +
> +static bool dw_hdmi_bridge_mode_fixup(struct drm_bridge *bridge,
> +				      const struct drm_display_mode *orig_mode,
> +				      struct drm_display_mode *mode)
> +{
> +	struct dw_hdmi *hdmi = bridge->driver_private;
> +	struct drm_connector *connector = &hdmi->connector;
> +	enum drm_mode_status status;
> +
> +	status = dw_hdmi_connector_mode_valid(connector, mode);
> +	if (status != MODE_OK)
> +		return false;
> +	return true;
> +}
> +
>  static void dw_hdmi_bridge_mode_set(struct drm_bridge *bridge,
>  				    struct drm_display_mode *orig_mode,
>  				    struct drm_display_mode *mode)
> @@ -1781,6 +1796,7 @@ static const struct drm_bridge_funcs dw_hdmi_bridge_funcs = {
>  	.enable = dw_hdmi_bridge_enable,
>  	.disable = dw_hdmi_bridge_disable,
>  	.mode_set = dw_hdmi_bridge_mode_set,
> +	.mode_fixup = dw_hdmi_bridge_mode_fixup,
>  };
>
>  static irqreturn_t dw_hdmi_i2c_irq(struct dw_hdmi *hdmi)
>

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