Re: [PATCH 1/3] drm/bridge: analogix_dp: deassert DP_PHY_PD on power-on for exynos

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 27.10.2026 13:01, Alexandre Marquet via B4 Relay wrote:
> From: Alexandre Marquet <tb@a-marquet.fr>
>
> On exynos platforms at least, calling
> analogix_dp_set_analog_power_down() to power on (with enable=false) CH0
> to CH3 or the AUX bus currently produces no effect, unless the function
> is first called to power on everything (by setting block to POWER_ALL or
> ANALOG_TOTAL). The reason for this is that DP_PHY_PD being asserted
> (which is its default state) renders every other register bit
> ineffective.
>
> This is particularly an issue for AUX bus initialization, that tends to
> happen before anything else (e.g., to request EDID), and thus, before
> anything has any chance to request a power on of the whole analog
> section of the chip.
>
> This commit allows analogix_dp_set_analog_power_down() to power on any
> block, by deasserting DP_PHY_PD if needed.
>
> Signed-off-by: Alexandre Marquet <tb@a-marquet.fr>

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

Snow, Peach-Pit and Peach-Pi Chromebooks work fine with this change.

> ---
>  drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
> index c1344a3f013a..9f634d4e4793 100644
> --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
> +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
> @@ -256,6 +256,19 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  	if (dp->plat_data && analogix_dp_is_rockchip(dp->plat_data->dev_type))
>  		phy_pd_addr = ANALOGIX_DP_PD;
>  
> +	reg = readl(dp->reg_base + phy_pd_addr);
> +
> +	if (dp->plat_data && (dp->plat_data->dev_type == EXYNOS_DP)) {
> +		/* On exynos, register AUX_PD and CH[0-3]_PD have no effect if
> +		 * DP_PHY_PD is asserted. So, when powering any of them up, we
> +		 * need to deassert DP_PHY_PD first.
> +		 */
> +		if (!enable && (reg & DP_PHY_PD)) {
> +			reg &= ~DP_PHY_PD;
> +			reg |= AUX_PD | CH0_PD | CH1_PD | CH2_PD | CH3_PD;
> +		}
> +	}
> +
>  	switch (block) {
>  	case AUX_BLOCK:
>  		if (dp->plat_data && analogix_dp_is_rockchip(dp->plat_data->dev_type))
> @@ -263,7 +276,6 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  		else
>  			mask = AUX_PD;
>  
> -		reg = readl(dp->reg_base + phy_pd_addr);
>  		if (enable)
>  			reg |= mask;
>  		else
> @@ -272,7 +284,6 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  		break;
>  	case CH0_BLOCK:
>  		mask = CH0_PD;
> -		reg = readl(dp->reg_base + phy_pd_addr);
>  
>  		if (enable)
>  			reg |= mask;
> @@ -282,7 +293,6 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  		break;
>  	case CH1_BLOCK:
>  		mask = CH1_PD;
> -		reg = readl(dp->reg_base + phy_pd_addr);
>  
>  		if (enable)
>  			reg |= mask;
> @@ -292,7 +302,6 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  		break;
>  	case CH2_BLOCK:
>  		mask = CH2_PD;
> -		reg = readl(dp->reg_base + phy_pd_addr);
>  
>  		if (enable)
>  			reg |= mask;
> @@ -302,7 +311,6 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  		break;
>  	case CH3_BLOCK:
>  		mask = CH3_PD;
> -		reg = readl(dp->reg_base + phy_pd_addr);
>  
>  		if (enable)
>  			reg |= mask;
> @@ -321,7 +329,6 @@ void analogix_dp_set_analog_power_down(struct analogix_dp_device *dp,
>  		else
>  			mask = DP_PHY_PD;
>  
> -		reg = readl(dp->reg_base + phy_pd_addr);
>  		if (enable)
>  			reg |= mask;
>  		else
>
Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland