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

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Message-ID: <80411ac4-6143-4c2e-bc9e-20a734f15987@oss.qualcomm.com>
Date: Fri, 16 Jan 2026 16:18:43 +0800
From: Yongxing Mou <yongxing.mou@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Vinod Koul <vkoul@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        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 1/14/2026 2:55 AM, Dmitry Baryshkov wrote:
> On Tue, Jan 13, 2026 at 08:04:06PM +0800, Yongxing Mou wrote:
>>
>>
>> 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?
> 
> All PHYs should support eDP and DP modes, so most of the configuration
> tables need to be updated/fixed. I tried going through all the tables,
> but I never had time to do it in a sane and complete way. As you started
> looking into it, would you please review programming for all chipsets
> starting from SC8180X?
> 
I don't got the SC8180X PHY HPG permission now. once i got it, will 
check it's configuration and see what i can do. But first i want to 
correct the LeMans and Hamoa configuration and post the LDO change. Do 
you mean switching between the eDP and DP mode tables based on is_edp, 
instead of using a fixed table?