Re: [PATCH v16 3/8] drm/mediatek: Add MT8195 Embedded DisplayPort driver

[CK Hu]

Hi, Bo-Chen:

On Fri, 2022-08-05 at 18:14 +0800, Bo-Chen Chen wrote:
> From: Markus Schneider-Pargmann <msp@xxxxxxxxxxxx>
> 
> 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@xxxxxxxxxxxx>
> 
> Signed-off-by: Markus Schneider-Pargmann <msp@xxxxxxxxxxxx>
> Signed-off-by: Guillaume Ranquet <granquet@xxxxxxxxxxxx>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@xxxxxxxxxxxx>
> Tested-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@xxxxxxxxxxxxx>
> Reviewed-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@xxxxxxxxxxxxx>
> ---

[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)

If the clock has pass the linkrate and land_count limitation, the clock
would be OK because the linkrate and lane_count is trained. Why need to
check 600000?

Regards,
CK

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