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

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Message-ID: <rffcbo7fxful5ciy5znmgdnrnoijeoyw3ysk7sxoop3pw4bnyw@httwc7pk4gks>
Date: Fri, 16 Jan 2026 10:41:48 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Yongxing Mou <yongxing.mou@....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 Fri, Jan 16, 2026 at 04:18:43PM +0800, Yongxing Mou wrote:
> 
> 
> 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?

Based on the PHY being used in the eDP or DP modes (it is related but
not equivalent to the is_edp).

-- 
With best wishes
Dmitry