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Thu, 30 Oct 2025 01:54:21 -0700 (PDT) Message-ID: Date: Thu, 30 Oct 2025 14:24:15 +0530 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 v1 1/1] arm64: dts: qcom: talos-evk: Add support for dual-channel LVDS panel To: Dmitry Baryshkov Cc: Konrad Dybcio , andersson@kernel.org, konradybcio@kernel.org, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org References: <20251028061636.724667-1-tessolveupstream@gmail.com> <20251028061636.724667-2-tessolveupstream@gmail.com> <9208d2ef-79da-4e80-ac1f-e01fa5feae0a@gmail.com> Content-Language: en-US From: Tessolve Upstream In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 29/10/25 18:04, Dmitry Baryshkov wrote: > On Wed, Oct 29, 2025 at 05:50:01PM +0530, Tessolve Upstream wrote: >> >> >> On 28/10/25 14:55, Konrad Dybcio wrote: >>> On 10/28/25 7:16 AM, Sudarshan Shetty wrote: >>>> This patch introduces a new device tree for the QCS615 Talos >>>> EVK platform with dual-channel LVDS display support. >>>> >>>> The new DTS file (`talos-evk-lvds.dts`) is based on the existing >>>> `talos-evk.dts` and extends it to enable a dual-channel LVDS display >>>> configuration using the TI SN65DSI84 DSI-to-LVDS bridge. >>>> >>>> where channel-A carries odd pixel and channel-B carries even pixel >>>> on the QCS615 talos evk platform. >>>> >>>> Signed-off-by: Sudarshan Shetty >>>> --- >>> >>> [...] >>> >>>> + backlight: backlight { >>>> + compatible = "gpio-backlight"; >>>> + gpios = <&tlmm 115 GPIO_ACTIVE_HIGH>; >>>> + default-on; >>>> + }; >>>> + >>>> + lcd0_pwm_en { >>> >>> Use hyphens instead of underscores in node names >> >> Okay, will update in next patch. >>> >>>> + compatible = "pwm-gpio"; >>>> + gpios = <&tlmm 59 GPIO_ACTIVE_HIGH>; >>>> + pinctrl-0 = <&lcd0_bklt_pwm>; >>> >>> I think your intention was to use pwm-backlight and wire this node >>> up to that >> >> Soc does not support the PWM interface hence we are using gpio >> as "pwm-gpio" by setting the duty cycle to 100%(i.e. "no pwm") > > Why do you mention PWM here at all? It's perfectly fine to use > gpio-backlight. That looks extremely suspicious since you are not > referecing the pwm-gpio device at all. Thanks for the feedback. GPIO59 (LED_PWM) connected to the panel’s dimming input. Since we can only drive the LED_PWM pin high (100% duty), it does not provide true PWM control. I’ll remove the non-standard "pwm-gpio" node and model both lines using the standard gpio-backlight binding, like this: backlight: backlight { compatible = "gpio-backlight"; gpios = <&tlmm 115 GPIO_ACTIVE_HIGH>, <&tlmm 59 GPIO_ACTIVE_HIGH>; default-on; pinctrl-0 = <&lcd0_bklt_en>, <&lcd0_bklt_pwm>; pinctrl-names = "default"; }; &tlmm { lcd0_bklt_en: lcd0-bklt-en-state { pins = "gpio115"; function = "gpio"; bias-disable; }; lcd0_bklt_pwm: lcd0-bklt-pwm-state { pins = "gpio59"; function = "gpio"; bias-disable; }; }; Let me know your opinion here, Thanks in advance. >