Subject: Re: [PATCH v2 4/4] drm/verisilicon: add Nuvoton MA35D1 DCU Lite display controller support

From: Joey Lu <[email-masked]>
Date: Wed, 20 May 2026 11:09:57 +0800

On 5/19/2026 3:44 PM, Icenowy Zheng wrote:
> 在 2026-05-19二的 13:51 +0800，Joey Lu写道：
>> The Nuvoton MA35D1 SoC integrates a Verisilicon DCU Lite display
>> controller.  While its register layout is broadly similar to the
>> DC8200,
>> several differences require dedicated hardware ops:
>>
>> 1. No CONFIG_EX commit path: framebuffer updates use enable (bit 0)
>> and
>>     reset (bit 4) bits in FB_CONFIG instead of the DC8200 staging
>> registers
>>     (FB_CONFIG_EX, FB_TOP_LEFT, FB_BOTTOM_RIGHT, FB_BLEND_CONFIG,
>>     PANEL_CONFIG_EX).
>>
>> 2. No PANEL_START register: panel output starts when
>>     PANEL_CONFIG.RUNNING is set; no multi-display sync start register
>>     is used.
>>
>> 3. Different IRQ registers: DCU Lite uses DISP_IRQ_STA (0x147C) /
>>     DISP_IRQ_EN (0x1480) versus DC8200's TOP_IRQ_ACK (0x0010) /
>>     TOP_IRQ_EN (0x0014).
>>
>> 4. Per-frame commit cycle: DCU Lite requires the VALID bit in
>> FB_CONFIG
>>     to be set at the start of each atomic commit (crtc_begin) and
>> cleared
>>     after (crtc_flush).
>>
>> 5. Simpler clock topology: only "core" (bus gate) and "pix0" (pixel
>>     divider) clocks; no axi or ahb clocks.  Make axi_clk and ahb_clk
>>     optional (devm_clk_get_optional_enabled) so DCU Lite nodes without
>>     those clocks are handled gracefully.
>>
>> Add vs_dcu_lite.c implementing the vs_dc_funcs vtable for the above
>> differences.  After chip identity detection, vs_dc_probe() now
>> selects
>> vs_dcu_lite_funcs when the identified model is VSDC_MODEL_DCU_LITE
>> (model register reads 0, revision 0x5560, customer_id 0x305).
>>
>> Extend Kconfig to allow building on ARCH_MA35 platforms.
>>
>> Signed-off-by: Joey Lu <[email-masked]>
>> ---
>>   drivers/gpu/drm/verisilicon/Kconfig       |  2 +-
>>   drivers/gpu/drm/verisilicon/Makefile      |  2 +-
>>   drivers/gpu/drm/verisilicon/vs_dc.c       |  9 ++-
>>   drivers/gpu/drm/verisilicon/vs_dc.h       |  1 +
>>   drivers/gpu/drm/verisilicon/vs_dcu_lite.c | 78
>> +++++++++++++++++++++++
>>   5 files changed, 87 insertions(+), 5 deletions(-)
>>   create mode 100644 drivers/gpu/drm/verisilicon/vs_dcu_lite.c
>>
>> diff --git a/drivers/gpu/drm/verisilicon/Kconfig
>> b/drivers/gpu/drm/verisilicon/Kconfig
>> index 7cce86ec8603..295d246eb4b4 100644
>> --- a/drivers/gpu/drm/verisilicon/Kconfig
>> +++ b/drivers/gpu/drm/verisilicon/Kconfig
>> @@ -2,7 +2,7 @@
>>   config DRM_VERISILICON_DC
>>   	tristate "DRM Support for Verisilicon DC-series display
>> controllers"
>>   	depends on DRM && COMMON_CLK
>> -	depends on RISCV || COMPILE_TEST
>> +	depends on RISCV || ARCH_MA35 || COMPILE_TEST
>>   	select DRM_BRIDGE_CONNECTOR
>>   	select DRM_CLIENT_SELECTION
>>   	select DRM_DISPLAY_HELPER
>> diff --git a/drivers/gpu/drm/verisilicon/Makefile
>> b/drivers/gpu/drm/verisilicon/Makefile
>> index f4fbd9f7d6a2..bf88f627e65c 100644
>> --- a/drivers/gpu/drm/verisilicon/Makefile
>> +++ b/drivers/gpu/drm/verisilicon/Makefile
>> @@ -1,5 +1,5 @@
>>   # SPDX-License-Identifier: GPL-2.0-only
>>   
>> -verisilicon-dc-objs := vs_bridge.o vs_crtc.o vs_dc.o vs_dc8200.o
>> vs_drm.o vs_hwdb.o vs_plane.o vs_primary_plane.o
>> +verisilicon-dc-objs := vs_bridge.o vs_crtc.o vs_dc.o vs_dc8200.o
>> vs_dcu_lite.o vs_drm.o vs_hwdb.o vs_plane.o vs_primary_plane.o
>>   
>>   obj-$(CONFIG_DRM_VERISILICON_DC) += verisilicon-dc.o
>> diff --git a/drivers/gpu/drm/verisilicon/vs_dc.c
>> b/drivers/gpu/drm/verisilicon/vs_dc.c
>> index c94957024189..77bc63c629f7 100644
>> --- a/drivers/gpu/drm/verisilicon/vs_dc.c
>> +++ b/drivers/gpu/drm/verisilicon/vs_dc.c
>> @@ -90,13 +90,13 @@ static int vs_dc_probe(struct platform_device
>> *pdev)
>>   		return PTR_ERR(dc->core_clk);
>>   	}
>>   
>> -	dc->axi_clk = devm_clk_get_enabled(dev, "axi");
>> +	dc->axi_clk = devm_clk_get_optional_enabled(dev, "axi");
>>   	if (IS_ERR(dc->axi_clk)) {
>>   		dev_err(dev, "can't get axi clock\n");
>>   		return PTR_ERR(dc->axi_clk);
>>   	}
>>   
>> -	dc->ahb_clk = devm_clk_get_enabled(dev, "ahb");
>> +	dc->ahb_clk = devm_clk_get_optional_enabled(dev, "ahb");
>>   	if (IS_ERR(dc->ahb_clk)) {
>>   		dev_err(dev, "can't get ahb clock\n");
>>   		return PTR_ERR(dc->ahb_clk);
>> @@ -134,7 +134,10 @@ static int vs_dc_probe(struct platform_device
>> *pdev)
>>   	dev_info(dev, "Found DC%x rev %x customer %x\n", dc-
>>> identity.model,
>>   		 dc->identity.revision, dc->identity.customer_id);
>>   
>> -	dc->funcs = &vs_dc8200_funcs;
>> +	if (dc->identity.model == VSDC_MODEL_DC8200)
> Don't do that. The model value is only for matching hardware values,
> not for detecting what's present. Don't forget that DC8000 has a model
> value of 0x8000, but behaves similarly with DCUltraLite with a model
> value of 0x0.
>
> I suggest adding another field for assigning helper functions.
>
> My suggestion is here:
>
> ```
> enum vs_dc_generation {
> 	VSDC_GEN_DC8000,
> 	VSDC_GEN_DC8200
> };
> ```
>
> Thanks,
> Icenowy
Understood. I will add `enum vs_dc_generation` to vs_hwdb.h and a 
`generation` field to `vs_chip_identity`. Each entry in 
`vs_chip_identities[]` will set `.generation` accordingly (DC8200 
entries → `VSDC_GEN_DC8200`; DCUltraLite → `VSDC_GEN_DC8000`). The probe 
will then branch on `dc->identity.generation == VSDC_GEN_DC8200` instead 
of the model register value.
>> +		dc->funcs = &vs_dc8200_funcs;
>> +	else
>> +		dc->funcs = &vs_dcu_lite_funcs;
>>   
>>   	if (port_count > dc->identity.display_count) {
>>   		dev_err(dev, "too many downstream ports than HW
>> capability\n");
>> diff --git a/drivers/gpu/drm/verisilicon/vs_dc.h
>> b/drivers/gpu/drm/verisilicon/vs_dc.h
>> index 45172c1a525c..d77d4a1babdf 100644
>> --- a/drivers/gpu/drm/verisilicon/vs_dc.h
>> +++ b/drivers/gpu/drm/verisilicon/vs_dc.h
>> @@ -66,5 +66,6 @@ struct vs_dc {
>>   };
>>   
>>   extern const struct vs_dc_funcs vs_dc8200_funcs;
>> +extern const struct vs_dc_funcs vs_dcu_lite_funcs;
>>   
>>   #endif /* _VS_DC_H_ */
>> diff --git a/drivers/gpu/drm/verisilicon/vs_dcu_lite.c
>> b/drivers/gpu/drm/verisilicon/vs_dcu_lite.c
>> new file mode 100644
>> index 000000000000..11ef57d5ebaa
>> --- /dev/null
>> +++ b/drivers/gpu/drm/verisilicon/vs_dcu_lite.c
>> @@ -0,0 +1,78 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Copyright (C) 2026 Joey Lu <[email-masked]>
>> + */
>> +
>> +#include <linux/regmap.h>
>> +
>> +#include "vs_crtc_regs.h"
>> +#include "vs_dc.h"
>> +#include "vs_primary_plane_regs.h"
>> +
>> +static void vs_dcu_lite_bridge_enable(struct vs_dc *dc, unsigned int
>> output)
>> +{
>> +	regmap_set_bits(dc->regs, VSDC_FB_CONFIG(output),
>> +			VSDC_FB_CONFIG_RESET);
>> +}
>> +
>> +static void vs_dcu_lite_bridge_disable(struct vs_dc *dc, unsigned
>> int output)
>> +{
>> +	regmap_clear_bits(dc->regs, VSDC_FB_CONFIG(output),
>> +			  VSDC_FB_CONFIG_RESET);
>> +}
>> +
>> +static void vs_dcu_lite_crtc_begin(struct vs_dc *dc, unsigned int
>> output)
>> +{
>> +	regmap_set_bits(dc->regs, VSDC_FB_CONFIG(output),
>> +			VSDC_FB_CONFIG_VALID);
>> +}
>> +
>> +static void vs_dcu_lite_crtc_flush(struct vs_dc *dc, unsigned int
>> output)
>> +{
>> +	regmap_clear_bits(dc->regs, VSDC_FB_CONFIG(output),
>> +			  VSDC_FB_CONFIG_VALID);
>> +}
>> +
>> +static void vs_dcu_lite_crtc_enable(struct vs_dc *dc, unsigned int
>> output)
>> +{
>> +	regmap_set_bits(dc->regs, VSDC_FB_CONFIG(output),
>> +			VSDC_FB_CONFIG_ENABLE);
>> +}
>> +
>> +static void vs_dcu_lite_crtc_disable(struct vs_dc *dc, unsigned int
>> output)
>> +{
>> +	regmap_clear_bits(dc->regs, VSDC_FB_CONFIG(output),
>> +			  VSDC_FB_CONFIG_ENABLE);
>> +}
>> +
>> +static void vs_dcu_lite_enable_vblank(struct vs_dc *dc, unsigned int
>> output)
>> +{
>> +	regmap_set_bits(dc->regs, VSDC_DISP_IRQ_EN,
>> +			VSDC_DISP_IRQ_VSYNC(output));
>> +}
>> +
>> +static void vs_dcu_lite_disable_vblank(struct vs_dc *dc, unsigned
>> int output)
>> +{
>> +	regmap_clear_bits(dc->regs, VSDC_DISP_IRQ_EN,
>> +			  VSDC_DISP_IRQ_VSYNC(output));
>> +}
>> +
>> +static u32 vs_dcu_lite_irq_handler(struct vs_dc *dc)
>> +{
>> +	u32 irqs;
>> +
>> +	regmap_read(dc->regs, VSDC_DISP_IRQ_STA, &irqs);
>> +	return irqs;
>> +}
>> +
>> +const struct vs_dc_funcs vs_dcu_lite_funcs = {
>> +	.bridge_enable		= vs_dcu_lite_bridge_enable,
>> +	.bridge_disable		=
>> vs_dcu_lite_bridge_disable,
>> +	.crtc_begin		= vs_dcu_lite_crtc_begin,
>> +	.crtc_flush		= vs_dcu_lite_crtc_flush,
>> +	.crtc_enable		= vs_dcu_lite_crtc_enable,
>> +	.crtc_disable		= vs_dcu_lite_crtc_disable,
>> +	.enable_vblank		= vs_dcu_lite_enable_vblank,
>> +	.disable_vblank		=
>> vs_dcu_lite_disable_vblank,
>> +	.irq_handler		= vs_dcu_lite_irq_handler,
>> +};