linux-kernel - Re: [PATCH v5 3/3] drm/msm/dp: retry 3 times if set sink to D0 poweer state failed

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Date:   Mon, 12 Sep 2022 21:37:20 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, swboyd@...omium.org, dianders@...omium.org,
        vkoul@...nel.org, daniel@...ll.ch, airlied@...ux.ie,
        agross@...nel.org, bjorn.andersson@...aro.org
Cc:     quic_abhinavk@...cinc.com, quic_sbillaka@...cinc.com,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] drm/msm/dp: retry 3 times if set sink to D0 poweer
 state failed

On 12/09/2022 19:23, Kuogee Hsieh wrote:
> Bring sink out of D3 (power down) mode into D0 (normal operation) mode
> by setting DP_SET_POWER_D0 bit to DP_SET_POWER dpcd register. This
> patch will retry 3 times if written to DP_SET_POWER register failed.

Could you please elaborate this change? Can the sink succeed in reading 
the DP_SET_POWER, but fail writing DP_SET_POWER?

> 
> Changes in v5:
> -- split into two patches
> 
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>   drivers/gpu/drm/msm/dp/dp_link.c | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
> index 9d5381d..4360728 100644
> --- a/drivers/gpu/drm/msm/dp/dp_link.c
> +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> @@ -50,6 +50,7 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
>   {
>   	u8 value;
>   	ssize_t len;
> +	int i;
>   
>   	if (link->revision < 0x11)
>   		return 0;
> @@ -61,11 +62,13 @@ static int dp_aux_link_power_up(struct drm_dp_aux *aux,
>   	value &= ~DP_SET_POWER_MASK;
>   	value |= DP_SET_POWER_D0;
>   
> -	len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
> -	if (len < 0)
> -		return len;
> -
> -	usleep_range(1000, 2000);
> +	/* retry for 1ms to give the sink time to wake up */
> +	for (i = 0; i < 3; i++) {
> +		len = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
> +		usleep_range(1000, 2000);
> +		if (len == 1)
> +			break;
> +	}
>   
>   	return 0;
>   }

-- 
With best wishes
Dmitry