linux-kernel - Re: [PATCH 07/12] drm/panel: Set sufficient voltage for panel nt37801

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Message-ID: <4bnvh2ydtrmejknzpsxoalxoyjpq5g5cjbrico5ezbek24r52s@u5zy6ekh6lps>
Date: Mon, 27 Oct 2025 14:22:04 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: yuanjiey <yuanjie.yang@....qualcomm.com>
Cc: robin.clark@....qualcomm.com, lumag@...nel.org, abhinav.kumar@...ux.dev,
        sean@...rly.run, marijn.suijten@...ainline.org, airlied@...il.com,
        simona@...ll.ch, maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
        tzimmermann@...e.de, robh@...nel.org, krzk+dt@...nel.org,
        conor+dt@...nel.org, quic_mkrishn@...cinc.com, jonathan@...ek.ca,
        quic_khsieh@...cinc.com, neil.armstrong@...aro.org,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, tingwei.zhang@....qualcomm.com,
        aiqun.yu@....qualcomm.com, yongxing.mou@....qualcomm.com
Subject: Re: [PATCH 07/12] drm/panel: Set sufficient voltage for panel nt37801

On Fri, Oct 24, 2025 at 02:00:50PM +0800, yuanjiey wrote:
> On Thu, Oct 23, 2025 at 03:14:38PM +0300, Dmitry Baryshkov wrote:
> > On Thu, Oct 23, 2025 at 04:06:04PM +0800, yuanjie yang wrote:
> > > From: Yuanjie Yang <yuanjie.yang@....qualcomm.com>
> > > 
> > > The NT37801 Sepc V1.0 chapter "5.7.1 Power On Sequence" states
> > > VDDI=1.65V~1.95V, so set sufficient voltage for panel nt37801.
> > > 
> > > Signed-off-by: Yongxing Mou <yongxing.mou@....qualcomm.com>
> > > Signed-off-by: Yuanjie Yang <yuanjie.yang@....qualcomm.com>
> > > ---
> > >  drivers/gpu/drm/panel/panel-novatek-nt37801.c | 5 +++++
> > >  1 file changed, 5 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/panel/panel-novatek-nt37801.c b/drivers/gpu/drm/panel/panel-novatek-nt37801.c
> > > index d6a37d7e0cc6..7eda16e0c1f9 100644
> > > --- a/drivers/gpu/drm/panel/panel-novatek-nt37801.c
> > > +++ b/drivers/gpu/drm/panel/panel-novatek-nt37801.c
> > > @@ -267,6 +267,11 @@ static int novatek_nt37801_probe(struct mipi_dsi_device *dsi)
> > >  	if (ret < 0)
> > >  		return ret;
> > >  
> > > +	ret = regulator_set_voltage(ctx->supplies[0].consumer,
> > > +				    1650000, 1950000);
> > 
> > This should be done in the DT. Limit the voltage per the user.
> Two reason:
> 1.
> I see https://patchwork.freedesktop.org/patch/354612/
> 
> panel panel-novatek-nt35510.c also use regulator_set_voltage set right voltage,
> so I do the same work.

Please look for the majority rather than the exceptions. Out of all
panel drivers only two set the voltage directly.

> 
> 2.     Kaanapali vddio regulator:
> 
> 		vreg_l12b_1p8: ldo12 {
> 			regulator-name = "vreg_l12b_1p8";
> 			regulator-min-microvolt = <1200000>;
> 			regulator-max-microvolt = <1800000>;
> 
> 	Voltage is from 1.2~.1.8 V , So I can not set it 1.65~1.95 V from DT(1.95V is beyond the allowed range).
> 	So I use regulator_set_voltage to set voltage, and regulator_set_voltage will choose the appropriate voltage.

DT has to list the voltage values that work for the devices on that
particular platform. So, ldo12 should be listing 1.64 - 1.8 V.

> 
> 
> Thanks,
> Yuanjie
> 
> > > +	if (ret < 0)
> > > +		return ret;
> > > +
> > >  	ctx->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_LOW);
> > >  	if (IS_ERR(ctx->reset_gpio))
> > >  		return dev_err_probe(dev, PTR_ERR(ctx->reset_gpio),
> > > -- 
> > > 2.34.1
> > > 
> > 
> > -- 
> > With best wishes
> > Dmitry

-- 
With best wishes
Dmitry