linux-kernel - Re: [PATCH] drm/msm/dp: Correct LeMans/Monaco DP phy Swing/Emphasis setting

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Message-ID: <5187dc04-a1a1-4537-9c80-aaa100dd0033@oss.qualcomm.com>
Date: Fri, 9 Jan 2026 10:58:44 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Yongxing Mou <yongxing.mou@....qualcomm.com>,
        Vinod Koul <vkoul@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>
Cc: linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: Correct LeMans/Monaco DP phy Swing/Emphasis
 setting

On 1/9/26 9:30 AM, Yongxing Mou wrote:
> Currently, the LeMans/Monaco DP PHY operates in DP mode rather than eDP
> mode. Per the PHY HPG, the Swing and Emphasis settings have been corrected
> to the appropriate DP-mode values.
> 
> Additionally, the HPG specifies that the LDO value should be set to 0 when
> in DP mode. These misconfigurations can lead to link training failures on
> certain dongles.
> 
> Signed-off-by: Yongxing Mou <yongxing.mou@....qualcomm.com>
> ---
>  drivers/phy/qualcomm/phy-qcom-edp.c | 27 ++++++++++++++++++++++++---
>  1 file changed, 24 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/phy/qualcomm/phy-qcom-edp.c b/drivers/phy/qualcomm/phy-qcom-edp.c
> index 13feab99feec..5b0d774bd715 100644
> --- a/drivers/phy/qualcomm/phy-qcom-edp.c
> +++ b/drivers/phy/qualcomm/phy-qcom-edp.c
> @@ -122,6 +122,13 @@ static const u8 dp_swing_hbr_rbr[4][4] = {
>  	{ 0x1f, 0xff, 0xff, 0xff }
>  };
>  
> +static const u8 dp_swing_hbr_rbr_v1[4][4] = {
> +	{ 0x07, 0x0f, 0x16, 0x1f },
> +	{ 0x11, 0x1e, 0x1f, 0xff },
> +	{ 0x16, 0x1f, 0xff, 0xff },
> +	{ 0x1f, 0xff, 0xff, 0xff }
> +};

For these platforms, I see 4 tables of settings:

(Low/High) Swing/Pre-em for (Low/High) HBR

None of them exactly match your change 

[...]

> -	ldo_config = edp->is_edp ? 0x0 : 0x1;
> +	ldo_config = !edp->is_edp ? 0x0 : 0x1;

You'll notice that this is further wrong, because for eDP, it should be
0x81 at low-swing-high-HBR and 0xc1 at low-swing-low-HBR, and 0 at both
cases of high-swing

Please split the LDO change into a separate commit because it touches
more platforms

Konrad