Re: [PATCH v14 05/10] drm/mediatek: Add MT8195 Embedded DisplayPort driver

CK Hu
2022-07-15T09:37:53Z

Hi, Bo-Chen:

On Tue, 2022-07-12 at 19:12 +0800, Bo-Chen Chen wrote:
> From: Markus Schneider-Pargmann <msp@baylibre.com>
>
> This patch adds a embedded displayport driver for the MediaTek mt8195
> SoC.
>
> It supports the MT8195, the embedded DisplayPort units. It offers
> DisplayPort 1.4 with up to 4 lanes.
>
> The driver creates a child device for the phy. The child device will
> never exist without the parent being active. As they are sharing a
> register range, the parent passes a regmap pointer to the child so
> that
> both can work with the same register range. The phy driver sets
> device
> data that is read by the parent to get the phy device that can be
> used
> to control the phy properties.
>
> This driver is based on an initial version by
> Jitao shi <jitao.shi@mediatek.com>
>
> Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
> Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
> ---

[snip]

> +
> +static enum drm_mode_status
> +mtk_dp_bridge_mode_valid(struct drm_bridge *bridge,
> + const struct drm_display_info *info,
> + const struct drm_display_mode *mode)
> +{
> + struct mtk_dp *mtk_dp = mtk_dp_from_bridge(bridge);
> + u32 rx_linkrate = (u32)mtk_dp->train_info.link_rate * 27000;
> + u32 bpp = info->color_formats & DRM_COLOR_FORMAT_YCBCR422 ? 16
> : 24;
> +
> + if (rx_linkrate * mtk_dp->train_info.lane_count < mode->clock *
> bpp / 8)
> + return MODE_CLOCK_HIGH;
> +
> + if (mode->clock > 600000)
> + return MODE_CLOCK_HIGH;
> +
> + if ((mode->clock * 1000) / (mode->htotal * mode->vtotal) >
> + MTK_VDOSYS1_MAX_FRAMERATE)

Why limit frame rate to 60fps? If the resolution is small enough, why
not support higher fps?

Regards,
CK

> + return MODE_CLOCK_HIGH;
> +
> + return MODE_OK;
> +}
> +