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[78.88.45.245]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b7240540d7csm437308766b.71.2025.11.05.02.02.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 05 Nov 2025 02:02:51 -0800 (PST) Message-ID: <03dce1ab-3ef4-4441-b363-ca0a58664e96@oss.qualcomm.com> Date: Wed, 5 Nov 2025 11:02:47 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] arm64: dts: qcom: Add backlight support for eDP panel To: Yongxing Mou , Bjorn Andersson , Konrad Dybcio , Rob Herring , Krzysztof Kozlowski , Conor Dooley Cc: linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20251028-hamoa_dvt_backlight-v1-1-97ecb8d0ad01@oss.qualcomm.com> <0cf2521b-8d05-42f0-aab8-35cd370e599e@oss.qualcomm.com> <8caa1cec-d881-4e77-8d77-be043f8d13d6@oss.qualcomm.com> <4d0f1892-8aa6-4282-8c36-75f1e46cbae1@oss.qualcomm.com> Content-Language: en-US From: Konrad Dybcio In-Reply-To: <4d0f1892-8aa6-4282-8c36-75f1e46cbae1@oss.qualcomm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Proofpoint-ORIG-GUID: lNkFZjNOD7wrN4sGvoRmeJm5OYKizWl3 X-Proofpoint-GUID: lNkFZjNOD7wrN4sGvoRmeJm5OYKizWl3 X-Authority-Analysis: v=2.4 cv=MK1tWcZl c=1 sm=1 tr=0 ts=690b20ce cx=c_pps a=qKBjSQ1v91RyAK45QCPf5w==:117 a=FpWmc02/iXfjRdCD7H54yg==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=KKAkSRfTAAAA:8 a=EUspDBNiAAAA:8 a=eZhEbVVfMUXm6rNhgUoA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=NFOGd7dJGGMPyQGDc5-O:22 a=cvBusfyB2V15izCimMoJ:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTA1MDA3MyBTYWx0ZWRfX/Km8VUns+EZw fqIjDUF4BiAHTBEGwpaGngy+lhEMvsi43gh5+aElgiuJd3rzAf296fXNIgDEhq+5Senc8+NO5+t Yk4pE0xCfPiER6f8TS4qQHUINQ7cvU43fqpEbLqPKyZ8MM3PbBrAsPiP3imNxpFp2XjvdNF1y1K nekeJFZwy1KzXs7eAf8PU+7TjYEHMA17NFsLOAsF0UY6KQTz9GpIokWeQZFcJtCSv8hmA6U84mS cS6yCn9RO6nE3Idwv8lJfT/+TQCSulNBX33Im9J6bjkooIkiTIB7MTLe1uTbT6JA1Vk8fx/vcO2 2s54DMEBRtAIevosBUSAAS/Y4Vc7DEKgheoDvf6Gk/8JIWx0uoxBJUYoSAoBR2YTutqlDPCBGBK DpziZ72vs49YgkxmIQCE4J9qvGBeXw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-05_04,2025-11-03_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 impostorscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 bulkscore=0 clxscore=1015 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2510240001 definitions=main-2511050073 On 11/5/25 10:58 AM, Yongxing Mou wrote: > > > On 10/30/2025 7:27 PM, Konrad Dybcio wrote: >> On 10/30/25 12:07 PM, Yongxing Mou wrote: >>> >>> >>> On 10/30/2025 5:41 PM, Konrad Dybcio wrote: >>>> On 10/30/25 10:08 AM, Yongxing Mou wrote: >>>>> >>>>> >>>>> On 10/28/2025 5:08 PM, Konrad Dybcio wrote: >>>>>> On 10/28/25 8:04 AM, Yongxing Mou wrote: >>>>>>> Previously, the eDP panel backlight was enabled via UEFI. Added backlight >>>>>>> control node in kernel DTS due to some meta may not enable the backlight. >>>>>>> >>>>>>> Aligned with other x1e80100-based platforms: the PWM signal is controlled >>>>>>> by PMK8550, and the backlight enable signal is handled by PMC8380. >>>>>>> >>>>>>> Signed-off-by: Yongxing Mou >>>>>>> --- >>>>>> >>>>>> The subject must say "hamoa-iot-evk:" >>>>> Thanks and got it , will fix it in next version.>> arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts | 55 ++++++++++++++++++++++++++++++ >>>>>>>     1 file changed, 55 insertions(+) >>>>>>> >>>>>>> diff --git a/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts b/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts >>>>>>> index 36dd6599402b4650b7f8ad2c0cd22212116a25fe..fda1b3a3c7673be74832c27849231cba4bc1f25f 100644 >>>>>>> --- a/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts >>>>>>> +++ b/arch/arm64/boot/dts/qcom/hamoa-iot-evk.dts >>>>>>> @@ -17,6 +17,16 @@ aliases { >>>>>>>             serial1 = &uart14; >>>>>>>         }; >>>>>>>     +    backlight: backlight { >>>>>>> +        compatible = "pwm-backlight"; >>>>>>> +        pwms = <&pmk8550_pwm 0 5000000>; >>>>>> >>>>>> Try adjusting the backlight value.. you'll find some funny behavior >>>>>> near the max level.. which reminds me I should send some fixes for >>>>>> some laptop DTs >>>>>> >>>>>    I tried sliding the backlight between the maximum and minimum values. It seems that at a certain sliding speed, when approaching the maximum value, there is some brightness flickering. Is this the phenomenon you’re referring to?> [...] >>>> >>>> "maybe" - for me it was the brightness actually going down beyond ~80% >>>> >>>> The issue is that the PWM hardware can't really do a period that's >>>> == 5000000 ns >>>> >>>> But it seems like this is no longer an issue since the driver now >>>> rounds up to the closest supported value, see last couple commits >>>> to drivers/leds/rgb/leds-qcom-lpg.c >>>> >>>> Konrad >>> Oh,thanks for sharing that. I saw the phenomenon you mentioned. Previously, my baseline had already merged this patch series: https://lore.kernel.org/all/20250305-leds-qcom-lpg-fix-max-pwm-on-hi-res-v4-0-bfe124a53a9f@linaro.org/, so I didn’t observe the ‘brightness actually going down beyond ~80%.’and just very slight flickering. After I reverted patches, it indeed appeared.  So here i want to confirm, >>> pwms = <&pmk8550_pwm 0 5000000> >>> can i keep the value 5000000 ? >> >> I think so.. perhaps make sure the period is appropriate for >> the backlight device at the other end since you mentioned it's >> flickering >> >> Konrad > Compared to ‘brightness actually going down beyond ~80%’, this is just a very slight flicker that only occurs when sliding the brightness bar at a specific speed.It won’t occur in most cases. Also tried another value pwms = <&pmk8550_pwm 0 4266537>, and it looks the same, so can we keep it at 5000000 here? As I said, just put whatever the backlight that the PWM controller outputs to expects. Konrad