[PATCH v2 0/4] Add support for OLED panel used on Snapdragon Lenovo T14s Gen6

[PATCH v2 0/4] Add support for OLED panel used on Snapdragon Lenovo T14s Gen6

[Christopher Obbard]

The Snapdragon Lenovo T14s Gen6 can be bought with a number of different
panels. This patch series adds support for the OLED model which has a
Samsung ATNA40YK20 panel.

The first patch documents the panel in the existing driver.

The second patch adds the missing HPD gpio to the T14s devicetree. I
think that this patch could be split into two; one patch for the pinctrl
addition and one patch for adding the hpd-gpio property to the T14s
panel. But that can come in V3.

The third patch adds the eDP panel to the T14s OLED devicetree.

The fourth (and final) patch works around a problem when reading the
eDP panel's maximum backlight value. Without this patch, the maximum
brightness is detected as 0, thus meaning the backlight is never enabled.
I expect this patch to need a few rounds of rework/testing on other
devices!

The raw EDID of the panel is:

00 ff ff ff ff ff ff 00 4c 83 9f 41 00 00 00 00
00 21 01 04 b5 1e 13 78 02 0c f1 ae 52 3c b9 23
0c 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01
01 01 01 01 01 01 ca fe 40 64 b0 08 18 70 20 08
88 00 2e bd 10 00 00 1b ca fe 40 64 b0 08 38 77
08 20 88 00 2e bd 10 00 00 1b 00 00 00 fe 00 53
44 43 20 20 20 20 20 20 20 20 20 20 00 00 00 fe
00 41 54 4e 41 34 30 59 4b 32 30 2d 30 20 01 cf
02 03 0f 00 e3 05 80 00 e6 06 05 01 74 60 07 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 b7

Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
---
Changes in v2:
- Use the existing atna33xc20 driver rather than panel-edp.
- Add eDP panel into OLED devicetree.
- Add patch to read the correct maximum brightness from the eDP panel.
- Link to v1: https://lore.kernel.org/r/20250320-wip-obbardc-qcom-t14s-oled-panel-v1-1-05bc4bdcd82a@linaro.org

---
Christopher Obbard (4):
      dt-bindings: display: panel: samsung,atna40yk20: document ATNA40YK20
      arm64: dts: qcom: x1e78100-t14s: add hpd gpio to LCD panel
      arm64: dts: qcom: x1e78100-t14s-oled: add eDP panel
      drm/dp: fallback to maximum when PWM bit count is zero

 .../bindings/display/panel/samsung,atna33xc20.yaml |  2 +
 .../qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts    | 10 +++++
 .../dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi    | 11 +++++
 drivers/gpu/drm/display/drm_dp_helper.c            | 51 ++++++++++++++--------
 4 files changed, 57 insertions(+), 17 deletions(-)
---
base-commit: b6ae34803e82511009e2b78dc4fd154330ecdc2d
change-id: 20250320-wip-obbardc-qcom-t14s-oled-panel-b74fed21d600

Best regards,
-- 
Christopher Obbard <christopher.obbard@linaro.org>

[PATCH v2 1/4] dt-bindings: display: panel: samsung,atna40yk20: document ATNA40YK20

[Christopher Obbard]

The Samsung ATNA40YK20 panel is a 14" AMOLED eDP panel. It is
similar to the ATNA33XC20 except that it is larger and has a
different resolution.

Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
---
 Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml b/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml
index 684c2896d2387077cf2d91cc5a025e0838c0f536..31f0c0f038e494234d896691f3cf0b9b7cd8842d 100644
--- a/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml
+++ b/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml
@@ -19,6 +19,8 @@ properties:
       - const: samsung,atna33xc20
       - items:
           - enum:
+              # Samsung 14" WQXGA+ (2880×1800 pixels) eDP AMOLED panel
+              - samsung,atna40yk20
               # Samsung 14.5" WQXGA+ (2880x1800 pixels) eDP AMOLED panel
               - samsung,atna45af01
               # Samsung 14.5" 3K (2944x1840 pixels) eDP AMOLED panel

-- 
2.49.0

Re: [PATCH v2 1/4] dt-bindings: display: panel: samsung,atna40yk20: document ATNA40YK20

[Krzysztof Kozlowski]

On Tue, Mar 25, 2025 at 07:21:26PM +0000, Christopher Obbard wrote:
> The Samsung ATNA40YK20 panel is a 14" AMOLED eDP panel. It is
> similar to the ATNA33XC20 except that it is larger and has a
> different resolution.
> 
> Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
> ---
>  Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml | 2 ++
>  1 file changed, 2 insertions(+)

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Best regards,
Krzysztof

Re: [PATCH v2 1/4] dt-bindings: display: panel: samsung,atna40yk20: document ATNA40YK20

[Doug Anderson]

Hi,

On Wed, Mar 26, 2025 at 1:08 AM Krzysztof Kozlowski <krzk@kernel.org> wrote:
>
> On Tue, Mar 25, 2025 at 07:21:26PM +0000, Christopher Obbard wrote:
> > The Samsung ATNA40YK20 panel is a 14" AMOLED eDP panel. It is
> > similar to the ATNA33XC20 except that it is larger and has a
> > different resolution.
> >
> > Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
> > ---
> >  Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml | 2 ++
> >  1 file changed, 2 insertions(+)
>
> Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Pushed this patch to drm-misc-next:

[1/4] dt-bindings: display: panel: samsung,atna40yk20: document ATNA40YK20
      commit: 1822532477cb5f007313de4c70079c09aaa270d5

[PATCH v2 2/4] arm64: dts: qcom: x1e78100-t14s: add hpd gpio to LCD panel

[Christopher Obbard]

The eDP panel has an HPD GPIO. Describe it in the devicetree.

Unfortunately I cannot test this on the non-OLED model since I
only have access to the model with OLED (which also uses the
HPD GPIO).

I believe this could be split into two patches; one adding the
pinctrl node and one adding the hpd gpio to the T14s devicetree.
But I will wait for your comments on this ;-).

Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
---
 arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
index 962fb050c55c4fd33f480a21a8c47a484d0c82b8..46c73f5c039ed982b553636cf8c4237a20ba7687 100644
--- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
+++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
@@ -980,8 +980,12 @@ &mdss_dp3 {
 	aux-bus {
 		panel: panel {
 			compatible = "edp-panel";
+			hpd-gpios = <&tlmm 119 GPIO_ACTIVE_HIGH>;
 			power-supply = <&vreg_edp_3p3>;
 
+			pinctrl-0 = <&edp_hpd_n_default>;
+			pinctrl-names = "default";
+
 			port {
 				edp_panel_in: endpoint {
 					remote-endpoint = <&mdss_dp3_out>;
@@ -1286,6 +1290,13 @@ hall_int_n_default: hall-int-n-state {
 		bias-disable;
 	};
 
+	edp_hpd_n_default: edp-hpd-n-state {
+		pins = "gpio119";
+		function = "gpio";
+		drive-strength = <2>;
+		bias-pull-up;
+	};
+
 	pcie4_default: pcie4-default-state {
 		clkreq-n-pins {
 			pins = "gpio147";

-- 
2.49.0

Re: [PATCH v2 2/4] arm64: dts: qcom: x1e78100-t14s: add hpd gpio to LCD panel

[Bryan O'Donoghue]

On 25/03/2025 19:21, Christopher Obbard wrote:
> The eDP panel has an HPD GPIO. Describe it in the devicetree.
> 
> Unfortunately I cannot test this on the non-OLED model since I
> only have access to the model with OLED (which also uses the
> HPD GPIO).
> 
> I believe this could be split into two patches; one adding the
> pinctrl node and one adding the hpd gpio to the T14s devicetree.
> But I will wait for your comments on this ;-).

There's nothing wrong with defining a pin when you also use it but 
emoji's in a commit log are surely verboten !

> 
> Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
> ---
>   arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> index 962fb050c55c4fd33f480a21a8c47a484d0c82b8..46c73f5c039ed982b553636cf8c4237a20ba7687 100644
> --- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> +++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s.dtsi
> @@ -980,8 +980,12 @@ &mdss_dp3 {
>   	aux-bus {
>   		panel: panel {
>   			compatible = "edp-panel";
> +			hpd-gpios = <&tlmm 119 GPIO_ACTIVE_HIGH>;
>   			power-supply = <&vreg_edp_3p3>;
> 
> +			pinctrl-0 = <&edp_hpd_n_default>;
> +			pinctrl-names = "default";
> +
>   			port {
>   				edp_panel_in: endpoint {
>   					remote-endpoint = <&mdss_dp3_out>;
> @@ -1286,6 +1290,13 @@ hall_int_n_default: hall-int-n-state {
>   		bias-disable;
>   	};
> 
> +	edp_hpd_n_default: edp-hpd-n-state {
> +		pins = "gpio119";
> +		function = "gpio";
> +		drive-strength = <2>;
> +		bias-pull-up;
> +	};
> +
>   	pcie4_default: pcie4-default-state {
>   		clkreq-n-pins {
>   			pins = "gpio147";
> 
> --
> 2.49.0
> 
> 
This definition looks consistent with the schematic to me.

Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>

Re: [PATCH v2 2/4] arm64: dts: qcom: x1e78100-t14s: add hpd gpio to LCD panel

[Abel Vesa]

On 25-03-25 19:21:27, Christopher Obbard wrote:
> The eDP panel has an HPD GPIO. Describe it in the devicetree.
> 
> Unfortunately I cannot test this on the non-OLED model since I
> only have access to the model with OLED (which also uses the
> HPD GPIO).
> 
> I believe this could be split into two patches; one adding the
> pinctrl node and one adding the hpd gpio to the T14s devicetree.
> But I will wait for your comments on this ;-).

You should definitely drop these two paragraphs entirely from the commit
message. Maybe add them to the cover letter.

Re: [PATCH v2 2/4] arm64: dts: qcom: x1e78100-t14s: add hpd gpio to LCD panel

[Christopher Obbard]

Hi Abel,

On Thu, 27 Mar 2025 at 07:51, Abel Vesa <abel.vesa@linaro.org> wrote:
>
> On 25-03-25 19:21:27, Christopher Obbard wrote:
> > The eDP panel has an HPD GPIO. Describe it in the devicetree.
> >
> > Unfortunately I cannot test this on the non-OLED model since I
> > only have access to the model with OLED (which also uses the
> > HPD GPIO).
> >
> > I believe this could be split into two patches; one adding the
> > pinctrl node and one adding the hpd gpio to the T14s devicetree.
> > But I will wait for your comments on this ;-).
>
> You should definitely drop these two paragraphs entirely from the commit
> message. Maybe add them to the cover letter.

Of course; I will do so in v3.
But hey, it made you both reply, so in a way my comment did work ;-).

Cheers!

Chris

[PATCH v2 3/4] arm64: dts: qcom: x1e78100-t14s-oled: add eDP panel

[Christopher Obbard]

Add the Samsung ATNA40YK20 eDP panel to the device tree for the
Snapdragon T14s OLED model.

Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
---
 .../arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts
index be65fafafa736a0401a5872c40f69cb20cfbbd90..753add73df41050565e71b9faafee62bb2031b75 100644
--- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts
+++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts
@@ -10,3 +10,13 @@ / {
 	compatible = "lenovo,thinkpad-t14s-oled", "lenovo,thinkpad-t14s",
 		     "qcom,x1e78100", "qcom,x1e80100";
 };
+
+&panel {
+	compatible = "samsung,atna40yk20", "samsung,atna33xc20";
+	enable-gpios = <&pmc8380_3_gpios 4 GPIO_ACTIVE_HIGH>;
+	hpd-gpios = <&tlmm 119 GPIO_ACTIVE_HIGH>;
+	power-supply = <&vreg_edp_3p3>;
+
+	pinctrl-0 = <&edp_bl_en>, <&edp_hpd_n_default>;
+	pinctrl-names = "default";
+};

-- 
2.49.0

Re: [PATCH v2 3/4] arm64: dts: qcom: x1e78100-t14s-oled: add eDP panel

[Dmitry Baryshkov]

On 25/03/2025 21:21, Christopher Obbard wrote:
> Add the Samsung ATNA40YK20 eDP panel to the device tree for the
> Snapdragon T14s OLED model.
> 
> Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
> ---
>   .../arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts
> index be65fafafa736a0401a5872c40f69cb20cfbbd90..753add73df41050565e71b9faafee62bb2031b75 100644
> --- a/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts
> +++ b/arch/arm64/boot/dts/qcom/x1e78100-lenovo-thinkpad-t14s-oled.dts
> @@ -10,3 +10,13 @@ / {
>   	compatible = "lenovo,thinkpad-t14s-oled", "lenovo,thinkpad-t14s",
>   		     "qcom,x1e78100", "qcom,x1e80100";
>   };
> +
> +&panel {
> +	compatible = "samsung,atna40yk20", "samsung,atna33xc20";
> +	enable-gpios = <&pmc8380_3_gpios 4 GPIO_ACTIVE_HIGH>;
> +	hpd-gpios = <&tlmm 119 GPIO_ACTIVE_HIGH>;
> +	power-supply = <&vreg_edp_3p3>;

Why do you need to repeat hpd-gpios and power-supply properties?

> +
> +	pinctrl-0 = <&edp_bl_en>, <&edp_hpd_n_default>;
> +	pinctrl-names = "default";
> +};
> 


-- 
With best wishes
Dmitry

[PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

[Christopher Obbard]

Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
valid non-zero MIN and MAX values. This patch reworks the logic to
fallback to the max value in such cases, ensuring correct backlight PWM
configuration even when the bit count value is not explicitly set.

This improves compatibility with eDP panels (e.g. Samsung ATNA40YK20
used on the Lenovo T14s Gen6 Snapdragon with OLED panel) which reports
DP_EDP_PWMGEN_BIT_COUNT as 0 but still provides valid non-zero MIN/MAX
values.

Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
---
 drivers/gpu/drm/display/drm_dp_helper.c | 51 ++++++++++++++++++++++-----------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..734b7b8e46394de21837cda6ca1b189413b25cd8 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -3964,7 +3964,7 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf
 {
 	int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
 	int ret;
-	u8 pn, pn_min, pn_max;
+	u8 pn, pn_min, pn_max, bl_caps;
 
 	if (!bl->aux_set)
 		return 0;
@@ -3975,8 +3975,40 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf
 			    aux->name, ret);
 		return -ENODEV;
 	}
-
 	pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
+	if (ret != 1) {
+		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n",
+			    aux->name, ret);
+		return 0;
+	}
+	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
+	if (ret != 1) {
+		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n",
+			    aux->name, ret);
+		return 0;
+	}
+	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
+
+	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_ADJUSTMENT_CAP, &bl_caps);
+	if (ret != 1) {
+		bl_caps = 0;
+		drm_dbg_kms(aux->drm_dev, "%s: Failed to read backlight adjustment cap: %d\n",
+			aux->name, ret);
+	}
+
+	/*
+	 * Some eDP panels report brightness byte count support, but the byte count
+	 * reading is 0 (e.g. Samsung ATNA40YK20) so in these cases use pn_max
+	 * for pn.
+	 */
+	if (!pn && (bl_caps & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
+	    && pn_max)
+		pn = pn_max;
+
 	bl->max = (1 << pn) - 1;
 	if (!driver_pwm_freq_hz)
 		return 0;
@@ -4003,21 +4035,6 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf
 	 * - FxP is within 25% of desired value.
 	 *   Note: 25% is arbitrary value and may need some tweak.
 	 */
-	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
-	if (ret != 1) {
-		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n",
-			    aux->name, ret);
-		return 0;
-	}
-	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
-	if (ret != 1) {
-		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n",
-			    aux->name, ret);
-		return 0;
-	}
-	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
-	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
-
 	/* Ensure frequency is within 25% of desired value */
 	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
 	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);

-- 
2.49.0

Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

[Dmitry Baryshkov]

On 25/03/2025 21:21, Christopher Obbard wrote:
> Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
> valid non-zero MIN and MAX values. This patch reworks the logic to
> fallback to the max value in such cases, ensuring correct backlight PWM
> configuration even when the bit count value is not explicitly set.

I don't think this matches the eDP standard. It tells to use MIN if 
BIT_COUNT is less than MIN, if I understand it correctly.

> 
> This improves compatibility with eDP panels (e.g. Samsung ATNA40YK20
> used on the Lenovo T14s Gen6 Snapdragon with OLED panel) which reports
> DP_EDP_PWMGEN_BIT_COUNT as 0 but still provides valid non-zero MIN/MAX
> values.
> 
> Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org>
> Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
> Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org>
> ---
>   drivers/gpu/drm/display/drm_dp_helper.c | 51 ++++++++++++++++++++++-----------
>   1 file changed, 34 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..734b7b8e46394de21837cda6ca1b189413b25cd8 100644
> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> @@ -3964,7 +3964,7 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf
>   {
>   	int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
>   	int ret;
> -	u8 pn, pn_min, pn_max;
> +	u8 pn, pn_min, pn_max, bl_caps;
>   
>   	if (!bl->aux_set)
>   		return 0;
> @@ -3975,8 +3975,40 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf
>   			    aux->name, ret);
>   		return -ENODEV;
>   	}
> -
>   	pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
> +	if (ret != 1) {
> +		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n",
> +			    aux->name, ret);
> +		return 0;
> +	}
> +	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
> +	if (ret != 1) {
> +		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n",
> +			    aux->name, ret);
> +		return 0;
> +	}
> +	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_ADJUSTMENT_CAP, &bl_caps);
> +	if (ret != 1) {
> +		bl_caps = 0;
> +		drm_dbg_kms(aux->drm_dev, "%s: Failed to read backlight adjustment cap: %d\n",
> +			aux->name, ret);
> +	}
> +
> +	/*
> +	 * Some eDP panels report brightness byte count support, but the byte count
> +	 * reading is 0 (e.g. Samsung ATNA40YK20) so in these cases use pn_max
> +	 * for pn.
> +	 */
> +	if (!pn && (bl_caps & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> +	    && pn_max)
> +		pn = pn_max;
> +
>   	bl->max = (1 << pn) - 1;
>   	if (!driver_pwm_freq_hz)
>   		return 0;
> @@ -4003,21 +4035,6 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf
>   	 * - FxP is within 25% of desired value.
>   	 *   Note: 25% is arbitrary value and may need some tweak.
>   	 */
> -	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
> -	if (ret != 1) {
> -		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n",
> -			    aux->name, ret);
> -		return 0;
> -	}
> -	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
> -	if (ret != 1) {
> -		drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n",
> -			    aux->name, ret);
> -		return 0;
> -	}
> -	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -
>   	/* Ensure frequency is within 25% of desired value */
>   	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
>   	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> 


-- 
With best wishes
Dmitry

Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

[Christopher Obbard]

Hi Dmitry,

On Tue, 25 Mar 2025 at 22:53, Dmitry Baryshkov
<dmitry.baryshkov@oss.qualcomm.com> wrote:
>
> On 25/03/2025 21:21, Christopher Obbard wrote:
> > Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
> > valid non-zero MIN and MAX values. This patch reworks the logic to
> > fallback to the max value in such cases, ensuring correct backlight PWM
> > configuration even when the bit count value is not explicitly set.
>
> I don't think this matches the eDP standard. It tells to use MIN if
> BIT_COUNT is less than MIN, if I understand it correctly.

Thanks for your comment; that's a good point.

I need to re-read this section of the spec; but at least on this
hardware I printed the values of the registers and it seems like
MIN and MAX are the same, so I could switch the patch around to use
MIN in the next version.

   drm_edp_backlight_probe_max: pn=0, pn_min=11, pn_max=11, bl_caps=134


diff --git a/drivers/gpu/drm/display/drm_dp_helper.c
b/drivers/gpu/drm/display/drm_dp_helper.c
index 6e519c58c2e84..2be2b00c8a531 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -4061,6 +4061,8 @@ drm_edp_backlight_probe_max(struct drm_dp_aux
*aux, struct drm_edp_backlight_inf
                        aux->name, ret);
        }

+       pr_info("%s: pn=%d, pn_min=%d, pn_max=%d, bl_caps=%d\n",
__func__, pn, pn_min, pn_max, bl_caps);
+
        /*
         * Some eDP panels report brightness byte count support, but
the byte count
         * reading is 0 (e.g. Samsung ATNA40YK20) so in these cases use pn_max

Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

[Dmitry Baryshkov]

On Wed, Mar 26, 2025 at 03:08:30PM +0000, Christopher Obbard wrote:
> Hi Dmitry,
> 
> On Tue, 25 Mar 2025 at 22:53, Dmitry Baryshkov
> <dmitry.baryshkov@oss.qualcomm.com> wrote:
> >
> > On 25/03/2025 21:21, Christopher Obbard wrote:
> > > Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
> > > valid non-zero MIN and MAX values. This patch reworks the logic to
> > > fallback to the max value in such cases, ensuring correct backlight PWM
> > > configuration even when the bit count value is not explicitly set.
> >
> > I don't think this matches the eDP standard. It tells to use MIN if
> > BIT_COUNT is less than MIN, if I understand it correctly.
> 
> Thanks for your comment; that's a good point.
> 
> I need to re-read this section of the spec; but at least on this
> hardware I printed the values of the registers and it seems like
> MIN and MAX are the same, so I could switch the patch around to use
> MIN in the next version.

SGTM.

-- 
With best wishes
Dmitry

Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

[Abel Vesa]

On 25-03-25 19:21:29, Christopher Obbard wrote:
> Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
> valid non-zero MIN and MAX values. This patch reworks the logic to
> fallback to the max value in such cases, ensuring correct backlight PWM
> configuration even when the bit count value is not explicitly set.
> 
> This improves compatibility with eDP panels (e.g. Samsung ATNA40YK20
> used on the Lenovo T14s Gen6 Snapdragon with OLED panel) which reports
> DP_EDP_PWMGEN_BIT_COUNT as 0 but still provides valid non-zero MIN/MAX
> values.
> 

Nit-pick: AFAICT, there is no relationship between this patch and the
rest. So it should've probably not be part of this patchset.

Re: [PATCH v2 4/4] drm/dp: fallback to maximum when PWM bit count is zero

[Christopher Obbard]

Right, the reason this was included in this series is because without
this patch the panel's backlight doesn't actually work. So for me it
was natural to include it. But happy to split it into its own series.

On Thu, 27 Mar 2025 at 08:05, Abel Vesa <abel.vesa@linaro.org> wrote:
>
> On 25-03-25 19:21:29, Christopher Obbard wrote:
> > Some eDP devices report DP_EDP_PWMGEN_BIT_COUNT as 0, but still provide
> > valid non-zero MIN and MAX values. This patch reworks the logic to
> > fallback to the max value in such cases, ensuring correct backlight PWM
> > configuration even when the bit count value is not explicitly set.
> >
> > This improves compatibility with eDP panels (e.g. Samsung ATNA40YK20
> > used on the Lenovo T14s Gen6 Snapdragon with OLED panel) which reports
> > DP_EDP_PWMGEN_BIT_COUNT as 0 but still provides valid non-zero MIN/MAX
> > values.
> >
>
> Nit-pick: AFAICT, there is no relationship between this patch and the
> rest. So it should've probably not be part of this patchset.