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

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Message-ID: <33d57a53-93b4-4ea3-a7bb-0b2015501bad@oss.qualcomm.com>
Date: Tue, 13 Jan 2026 20:04:06 +0800
From: Yongxing Mou <yongxing.mou@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....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 1/9/2026 5:58 PM, Konrad Dybcio wrote:
> 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
> 
Emm, this table is in LeMans eDP HPG, here are 6 tables. 4 of them use 
for eDP mode and reset 2 tables used for DP mode. If my understanding is 
incorrect, please correct me. Thanks ~~~ > [...]
> 
>> -	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
> 

Yes, you are right, here seems something not correct. i will separate 
this change into single one.Here are some parts I don't fully understand 
here. Could you please point it? How do we know whether it is in 
low‑swing or high‑swing. I didn’t see any logic in the current code that 
determines this. Also, the value in Hamoa seems not same with LeMans,it 
is 0x51 and 0x91.

While going through the Hamoa HPG, I noticed a potential issue.

  static struct qcom_edp_phy_cfg x1e80100_phy_cfg = {
	.aux_cfg = edp_phy_aux_cfg_v4,
	.vco_div_cfg = edp_phy_vco_div_cfg_v4,
	.swing_pre_emph_cfg = &dp_phy_swing_pre_emph_cfg,...It use 
dp_phy_swing_pre_emph_cfg not edp_phy_swing_pre_emph_cfg, but Hamoa 
really use edp-panel here.. so does this phy cfg correct here?