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

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Message-ID: <e758dc56-a5eb-4c4a-9ab0-74e9b9b86c7c@oss.qualcomm.com>
Date: Fri, 31 Oct 2025 17:43:26 +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 31/10/2025 04:21, yuanjiey wrote:
> On Thu, Oct 30, 2025 at 07:57:46PM +0200, Dmitry Baryshkov wrote:
>> On Thu, Oct 30, 2025 at 10:08:30AM +0800, yuanjiey wrote:
>>> On Wed, Oct 29, 2025 at 02:20:13PM +0200, Dmitry Baryshkov wrote:
>>>> On Wed, Oct 29, 2025 at 09:58:39AM +0800, yuanjiey wrote:
>>>>> On Mon, Oct 27, 2025 at 02:22:04PM +0200, Dmitry Baryshkov wrote:
>>>>>> 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.
>>>>> get it. I check downstream DT,
>>>>>    dosnstream DT:
>>>>>     regulator-min-microvolt = <1800000>;
>>>>>     regulator-max-microvolt = <1800000>;
>>>>>
>>>>>    I test 1.8V works, So I will add 1.8V in next patch, do you think it is ok?
>>>>
>>>> What does panel's datasheet say?
>>>
>>> The NT37801 Sepc V1.0 chapter "5.7.1 Power On Sequence" states
>>> VDDI=1.65V~1.95V.
>>>
>>> So I should follow datasheet to set DT ldo12: 1.64 - 1.8V ?
>>
>> If the panel declares minimum voltage to 1.65 V, why are you declaring
>> 1.64 V as the mimimal voltage for the rail?
> 
> Corrcet here:
> 
> DT ldo12 will be  1.65 - 1.8V

Yep.

> 
> Thanks,
> Yuanjie
> 
>   
>>>
>>> if you think it is ture, I will fix it in next patch.
>> -- 
>> With best wishes
>> Dmitry


-- 
With best wishes
Dmitry