[PATCH v5 11/36] drm/bridge: analogix_dp: Wait for HPD signal before configuring link

[Archit Taneja]

On Saturday 10 March 2018 03:53 AM, Enric Balletbo i Serra wrote:
> From: zain wang <wzz at rock-chips.com>
> 
> According to DP spec v1.3 chap 3.5.1.2 Link Training, Link Policy Maker
> must first detect that the HPD signal is asserted high by the Downstream
> Device before establishing a link with it.

Reviewed-by: Archit Taneja <architt at codeaurora.org>

Thanks,
Archit

> 
> Cc: Stéphane Marchesin <marcheu at chromium.org>
> Signed-off-by: zain wang <wzz at rock-chips.com>
> Signed-off-by: Sean Paul <seanpaul at chromium.org>
> Signed-off-by: Thierry Escande <thierry.escande at collabora.com>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo at collabora.com>
> Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>
> ---
> 
>   drivers/gpu/drm/bridge/analogix/analogix_dp_core.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> index c81733b8185e..92fb9a072cb6 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> @@ -1169,6 +1169,17 @@ static int analogix_dp_set_bridge(struct analogix_dp_device *dp)
>   	if (ret)
>   		goto out_dp_init;
>   
> +	/*
> +	 * According to DP spec v1.3 chap 3.5.1.2 Link Training,
> +	 * We should first make sure the HPD signal is asserted high by device
> +	 * when we want to establish a link with it.
> +	 */
> +	ret = analogix_dp_detect_hpd(dp);
> +	if (ret) {
> +		DRM_ERROR("failed to get hpd single ret = %d\n", ret);
> +		goto out_dp_init;
> +	}
> +
>   	ret = analogix_dp_commit(dp);
>   	if (ret)
>   		goto out_dp_init;
>