[PATCH v2 RESEND 0/3] Add LVDS display support and PLL handling

[PATCH v2 RESEND 0/3] Add LVDS display support and PLL handling

[Manikandan Muralidharan]

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Hi all,

This patch series adds LVDS display support for the Atmel HLCDC driver
and introduces proper handling of the LVDS PLL clock required for such
panels.

The Atmel XLCDC IP supports multiple output types — Parallel RGB, MIPI
DSI, and LVDS. While the existing implementation handles RGB and MIPI
displays using the LCD generic clock (sys_clk), LVDS panels require the
dedicated LVDS PLL clock (lvds_pll_clk).Configuring the LVDS PLL clock
rate automatically based on the panel pixel clock, eliminates the need
for assigned-clock-rates entries in the device tree

Change logs are mentioned in individual patches

Dharma Balasubiramani (2):
  drm: atmel-hlcdc: add support for LVDS encoder type
  drm: atmel-hlcdc: set LVDS PLL clock rate for LVDS Displays

Manikandan Muralidharan (1):
  mfd: atmel-hlcdc: fetch LVDS PLL clock for LVDS display

 .../gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c    | 86 +++++++++++++++++--
 drivers/mfd/atmel-hlcdc.c                     | 16 +++-
 include/linux/mfd/atmel-hlcdc.h               |  1 +
 3 files changed, 95 insertions(+), 8 deletions(-)


base-commit: c1a7cc00cd412505e070eb4e62bc0b0ca85243e0
-- 
2.25.1

[PATCH v2 RESEND 1/3] drm: atmel-hlcdc: add support for LVDS encoder type

[Manikandan Muralidharan]

From: Dharma Balasubiramani <dharma.b@microchip.com>

Add support for encoder type "DRM_MODE_ENCODER_LVDS" with the following
bus formats:
	- RGB888_1X7X4_SPWG
	- RGB888_1X7X4_JEIDA
	- RGB666_1X7X3_SPWG
	- RGB666_1X18

Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
[manikandan.m@microchip.com: move modifications inside the
atmel_xlcdc_connector_output_lvds fn]
Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
---
 .../gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c    | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
index e0efc7309b1b..beb825fc4d5d 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
@@ -357,6 +357,42 @@ static int atmel_xlcdc_connector_output_dsi(struct drm_encoder *encoder,
 	return supported_fmts;
 }
 
+static int atmel_xlcdc_connector_output_lvds(struct drm_encoder *encoder,
+					     struct drm_display_info *info)
+{
+	int j;
+	unsigned int supported_fmts = 0;
+
+	switch (atmel_hlcdc_encoder_get_bus_fmt(encoder)) {
+	case 0:
+		break;
+	case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
+	case MEDIA_BUS_FMT_RGB666_1X18:
+		return ATMEL_HLCDC_RGB666_OUTPUT;
+	case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
+	case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
+		return ATMEL_HLCDC_RGB888_OUTPUT;
+	default:
+		return -EINVAL;
+	}
+
+	for (j = 0; j < info->num_bus_formats; j++) {
+		switch (info->bus_formats[j]) {
+		case MEDIA_BUS_FMT_RGB666_1X7X3_SPWG:
+		case MEDIA_BUS_FMT_RGB666_1X18:
+			supported_fmts |= ATMEL_HLCDC_RGB666_OUTPUT;
+			break;
+		case MEDIA_BUS_FMT_RGB888_1X7X4_SPWG:
+		case MEDIA_BUS_FMT_RGB888_1X7X4_JEIDA:
+			supported_fmts |= ATMEL_HLCDC_RGB888_OUTPUT;
+			break;
+		default:
+			break;
+		}
+	}
+	return supported_fmts;
+}
+
 static int atmel_hlcdc_connector_output_mode(struct drm_connector_state *state)
 {
 	struct drm_connector *connector = state->connector;
@@ -375,6 +411,8 @@ static int atmel_hlcdc_connector_output_mode(struct drm_connector_state *state)
 	 */
 	if (encoder->encoder_type == DRM_MODE_ENCODER_DSI)
 		return atmel_xlcdc_connector_output_dsi(encoder, info);
+	else if (encoder->encoder_type == DRM_MODE_ENCODER_LVDS)
+		return atmel_xlcdc_connector_output_lvds(encoder, info);
 
 	switch (atmel_hlcdc_encoder_get_bus_fmt(encoder)) {
 	case 0:
-- 
2.25.1

[PATCH v2 RESEND 2/3] mfd: atmel-hlcdc: fetch LVDS PLL clock for LVDS display

[Manikandan Muralidharan]

The XLCDC IP supports parallel RGB, MIPI DSI and LVDS Display.
The LCD Generic clock (sys_clk) is used for Parallel RGB and MIPI
displays, while the LVDS PLL clock (lvds_pll_clk) is used for LVDS
displays.Since both the clocks cannot co-exist together in the DT
for a given display, this patch first attempts to retrieve sys_clk
If that fails,it then tries to acquire lvds_pll_clk.

Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
---
changes in v2:
- Rephrase the comments, commit message and err logs
- Replace dev_err wwith dev_warn
- Remove Initializing sys_clk and lvds_pll_clk to NULL post
devm_kzalloc() call

---
 drivers/mfd/atmel-hlcdc.c       | 16 ++++++++++++++--
 include/linux/mfd/atmel-hlcdc.h |  1 +
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/atmel-hlcdc.c b/drivers/mfd/atmel-hlcdc.c
index 4c4e35d404f3..f680392b01ba 100644
--- a/drivers/mfd/atmel-hlcdc.c
+++ b/drivers/mfd/atmel-hlcdc.c
@@ -108,10 +108,22 @@ static int atmel_hlcdc_probe(struct platform_device *pdev)
 		return PTR_ERR(hlcdc->periph_clk);
 	}
 
+	/*
+	 * Retrieve any one of the Main clk required by the LCD to operate:
+	 *
+	 * LCDC Generic Clock (sys_clk) - Parallel RGB and MIPI displays,
+	 * LVDS PLL (lvds_pll_clk)      - LVDS display
+	 */
 	hlcdc->sys_clk = devm_clk_get(dev, "sys_clk");
 	if (IS_ERR(hlcdc->sys_clk)) {
-		dev_err(dev, "failed to get system clock\n");
-		return PTR_ERR(hlcdc->sys_clk);
+		dev_warn(dev,
+			 "failed to get LCDC generic clock, trying for LVDS PLL clock instead\n");
+
+		hlcdc->lvds_pll_clk = devm_clk_get(dev, "lvds_pll_clk");
+		if (IS_ERR(hlcdc->lvds_pll_clk)) {
+			dev_err(dev, "failed to get LVDS PLL clock\n");
+			return PTR_ERR(hlcdc->lvds_pll_clk);
+		}
 	}
 
 	hlcdc->slow_clk = devm_clk_get(dev, "slow_clk");
diff --git a/include/linux/mfd/atmel-hlcdc.h b/include/linux/mfd/atmel-hlcdc.h
index 80d675a03b39..07c2081867fd 100644
--- a/include/linux/mfd/atmel-hlcdc.h
+++ b/include/linux/mfd/atmel-hlcdc.h
@@ -75,6 +75,7 @@
  */
 struct atmel_hlcdc {
 	struct regmap *regmap;
+	struct clk *lvds_pll_clk;
 	struct clk *periph_clk;
 	struct clk *sys_clk;
 	struct clk *slow_clk;
-- 
2.25.1

[PATCH v2 RESEND 3/3] drm: atmel-hlcdc: set LVDS PLL clock rate for LVDS Displays

[Manikandan Muralidharan]

From: Dharma Balasubiramani <dharma.b@microchip.com>

The LVDS PLL clock runs at 7 times the panel pixel clock.
For LVDS displays, the PLL clock rate is set based on the
panel pixel clock, eliminating the need for the assigned-clock-rates
Device Tree property for lvds_pll_clk in the LCD node.

Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
---
Changes in v2:
- Rephrase commit message and comment block
---
 .../gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c    | 48 ++++++++++++++++---
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
index beb825fc4d5d..67860947c466 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
@@ -100,9 +100,15 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
 		drm_connector_list_iter_end(&iter);
 	}
 
-	ret = clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
-	if (ret)
-		return;
+	if (crtc->dc->hlcdc->lvds_pll_clk) {
+		ret = clk_prepare_enable(crtc->dc->hlcdc->lvds_pll_clk);
+		if (ret)
+			return;
+	} else {
+		ret = clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
+		if (ret)
+			return;
+	}
 
 	vm.vfront_porch = adj->crtc_vsync_start - adj->crtc_vdisplay;
 	vm.vback_porch = adj->crtc_vtotal - adj->crtc_vsync_end;
@@ -187,7 +193,10 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc *c)
 			   ATMEL_XLCDC_DPI : ATMEL_HLCDC_MODE_MASK),
 			   cfg);
 
-	clk_disable_unprepare(crtc->dc->hlcdc->sys_clk);
+	if (crtc->dc->hlcdc->lvds_pll_clk)
+		clk_disable_unprepare(crtc->dc->hlcdc->lvds_pll_clk);
+	else
+		clk_disable_unprepare(crtc->dc->hlcdc->sys_clk);
 }
 
 static enum drm_mode_status
@@ -243,7 +252,11 @@ static void atmel_hlcdc_crtc_atomic_disable(struct drm_crtc *c,
 				    10, 1000))
 		drm_warn(dev, "Atmel LCDC status register CLKSTS timeout\n");
 
-	clk_disable_unprepare(crtc->dc->hlcdc->sys_clk);
+	if (crtc->dc->hlcdc->lvds_pll_clk)
+		clk_disable_unprepare(crtc->dc->hlcdc->lvds_pll_clk);
+	else
+		clk_disable_unprepare(crtc->dc->hlcdc->sys_clk);
+
 	pinctrl_pm_select_sleep_state(dev->dev);
 
 	pm_runtime_allow(dev->dev);
@@ -256,15 +269,38 @@ static void atmel_hlcdc_crtc_atomic_enable(struct drm_crtc *c,
 {
 	struct drm_device *dev = c->dev;
 	struct atmel_hlcdc_crtc *crtc = drm_crtc_to_atmel_hlcdc_crtc(c);
+	struct drm_display_mode *adj = &c->state->adjusted_mode;
 	struct regmap *regmap = crtc->dc->hlcdc->regmap;
 	unsigned int status;
+	int ret;
 
 	pm_runtime_get_sync(dev->dev);
 
 	pm_runtime_forbid(dev->dev);
 
 	pinctrl_pm_select_default_state(dev->dev);
-	clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
+
+	if (crtc->dc->hlcdc->lvds_pll_clk) {
+		/*
+		 * For LVDS displays, retrieve the pixel clock from the panel
+		 * and set the LVDS PLL clock rate accordingly.
+		 * According to the datasheet,the LVDS PLL clock is 7 times the pixel clock.
+		 */
+		ret = clk_set_rate(crtc->dc->hlcdc->lvds_pll_clk,
+				   (adj->clock * 7 * 1000));
+		if (ret) {
+			dev_err(dev->dev, "Failed to set LVDS PLL clk rate: %d\n", ret);
+			return;
+		}
+
+		ret = clk_prepare_enable(crtc->dc->hlcdc->lvds_pll_clk);
+		if (ret)
+			return;
+	} else {
+		ret = clk_prepare_enable(crtc->dc->hlcdc->sys_clk);
+		if (ret)
+			return;
+	}
 
 	regmap_write(regmap, ATMEL_HLCDC_EN, ATMEL_HLCDC_PIXEL_CLK);
 	if (regmap_read_poll_timeout(regmap, ATMEL_HLCDC_SR, status,
-- 
2.25.1

Re: [PATCH v2 RESEND 2/3] mfd: atmel-hlcdc: fetch LVDS PLL clock for LVDS display

[Lee Jones]

On Wed, 22 Oct 2025, Manikandan Muralidharan wrote:

> The XLCDC IP supports parallel RGB, MIPI DSI and LVDS Display.
> The LCD Generic clock (sys_clk) is used for Parallel RGB and MIPI
> displays, while the LVDS PLL clock (lvds_pll_clk) is used for LVDS
> displays.Since both the clocks cannot co-exist together in the DT
> for a given display, this patch first attempts to retrieve sys_clk
> If that fails,it then tries to acquire lvds_pll_clk.
> 
> Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
> Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
> ---
> changes in v2:
> - Rephrase the comments, commit message and err logs
> - Replace dev_err wwith dev_warn
> - Remove Initializing sys_clk and lvds_pll_clk to NULL post
> devm_kzalloc() call
> 
> ---
>  drivers/mfd/atmel-hlcdc.c       | 16 ++++++++++++++--
>  include/linux/mfd/atmel-hlcdc.h |  1 +
>  2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mfd/atmel-hlcdc.c b/drivers/mfd/atmel-hlcdc.c
> index 4c4e35d404f3..f680392b01ba 100644
> --- a/drivers/mfd/atmel-hlcdc.c
> +++ b/drivers/mfd/atmel-hlcdc.c
> @@ -108,10 +108,22 @@ static int atmel_hlcdc_probe(struct platform_device *pdev)
>  		return PTR_ERR(hlcdc->periph_clk);
>  	}
>  
> +	/*
> +	 * Retrieve any one of the Main clk required by the LCD to operate:
> +	 *
> +	 * LCDC Generic Clock (sys_clk) - Parallel RGB and MIPI displays,
> +	 * LVDS PLL (lvds_pll_clk)      - LVDS display
> +	 */
>  	hlcdc->sys_clk = devm_clk_get(dev, "sys_clk");
>  	if (IS_ERR(hlcdc->sys_clk)) {
> -		dev_err(dev, "failed to get system clock\n");
> -		return PTR_ERR(hlcdc->sys_clk);
> +		dev_warn(dev,
> +			 "failed to get LCDC generic clock, trying for LVDS PLL clock instead\n");

Does the user really care which clock they use?

Can this just happen silently instead?

> +		hlcdc->lvds_pll_clk = devm_clk_get(dev, "lvds_pll_clk");
> +		if (IS_ERR(hlcdc->lvds_pll_clk)) {
> +			dev_err(dev, "failed to get LVDS PLL clock\n");

Failed to obtain both the LCDC (generic) and LVDS PLL clocks

> +			return PTR_ERR(hlcdc->lvds_pll_clk);
> +		}
>  	}
>  
>  	hlcdc->slow_clk = devm_clk_get(dev, "slow_clk");
> diff --git a/include/linux/mfd/atmel-hlcdc.h b/include/linux/mfd/atmel-hlcdc.h
> index 80d675a03b39..07c2081867fd 100644
> --- a/include/linux/mfd/atmel-hlcdc.h
> +++ b/include/linux/mfd/atmel-hlcdc.h
> @@ -75,6 +75,7 @@
>   */
>  struct atmel_hlcdc {
>  	struct regmap *regmap;
> +	struct clk *lvds_pll_clk;
>  	struct clk *periph_clk;
>  	struct clk *sys_clk;
>  	struct clk *slow_clk;
> -- 
> 2.25.1
> 

-- 
Lee Jones [李琼斯]

Re: [PATCH v2 RESEND 2/3] mfd: atmel-hlcdc: fetch LVDS PLL clock for LVDS display

[Manikandan.M]

Hi Lee,

On 06/11/25 6:32 pm, Lee Jones wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Wed, 22 Oct 2025, Manikandan Muralidharan wrote:
> 
>> The XLCDC IP supports parallel RGB, MIPI DSI and LVDS Display.
>> The LCD Generic clock (sys_clk) is used for Parallel RGB and MIPI
>> displays, while the LVDS PLL clock (lvds_pll_clk) is used for LVDS
>> displays.Since both the clocks cannot co-exist together in the DT
>> for a given display, this patch first attempts to retrieve sys_clk
>> If that fails,it then tries to acquire lvds_pll_clk.
>>
>> Signed-off-by: Manikandan Muralidharan <manikandan.m@microchip.com>
>> Signed-off-by: Dharma Balasubiramani <dharma.b@microchip.com>
>> ---
>> changes in v2:
>> - Rephrase the comments, commit message and err logs
>> - Replace dev_err wwith dev_warn
>> - Remove Initializing sys_clk and lvds_pll_clk to NULL post
>> devm_kzalloc() call
>>
>> ---
>>   drivers/mfd/atmel-hlcdc.c       | 16 ++++++++++++++--
>>   include/linux/mfd/atmel-hlcdc.h |  1 +
>>   2 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/mfd/atmel-hlcdc.c b/drivers/mfd/atmel-hlcdc.c
>> index 4c4e35d404f3..f680392b01ba 100644
>> --- a/drivers/mfd/atmel-hlcdc.c
>> +++ b/drivers/mfd/atmel-hlcdc.c
>> @@ -108,10 +108,22 @@ static int atmel_hlcdc_probe(struct platform_device *pdev)
>>                return PTR_ERR(hlcdc->periph_clk);
>>        }
>>
>> +     /*
>> +      * Retrieve any one of the Main clk required by the LCD to operate:
>> +      *
>> +      * LCDC Generic Clock (sys_clk) - Parallel RGB and MIPI displays,
>> +      * LVDS PLL (lvds_pll_clk)      - LVDS display
>> +      */
>>        hlcdc->sys_clk = devm_clk_get(dev, "sys_clk");
>>        if (IS_ERR(hlcdc->sys_clk)) {
>> -             dev_err(dev, "failed to get system clock\n");
>> -             return PTR_ERR(hlcdc->sys_clk);
>> +             dev_warn(dev,
>> +                      "failed to get LCDC generic clock, trying for LVDS PLL clock instead\n");
> 
> Does the user really care which clock they use?
> 
> Can this just happen silently instead?
> 
>> +             hlcdc->lvds_pll_clk = devm_clk_get(dev, "lvds_pll_clk");
>> +             if (IS_ERR(hlcdc->lvds_pll_clk)) {
>> +                     dev_err(dev, "failed to get LVDS PLL clock\n");
> 
> Failed to obtain both the LCDC (generic) and LVDS PLL clocks
> 
Thankyou, I will make sure v3 addresses these comments.

>> +                     return PTR_ERR(hlcdc->lvds_pll_clk);
>> +             }
>>        }
>>
>>        hlcdc->slow_clk = devm_clk_get(dev, "slow_clk");
>> diff --git a/include/linux/mfd/atmel-hlcdc.h b/include/linux/mfd/atmel-hlcdc.h
>> index 80d675a03b39..07c2081867fd 100644
>> --- a/include/linux/mfd/atmel-hlcdc.h
>> +++ b/include/linux/mfd/atmel-hlcdc.h
>> @@ -75,6 +75,7 @@
>>    */
>>   struct atmel_hlcdc {
>>        struct regmap *regmap;
>> +     struct clk *lvds_pll_clk;
>>        struct clk *periph_clk;
>>        struct clk *sys_clk;
>>        struct clk *slow_clk;
>> --
>> 2.25.1
>>
> 
> --
> Lee Jones [李琼斯]

-- 
Thanks and Regards,
Manikandan M.