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[60.250.196.139]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c82bb0ff0edsm4688486a12.20.2026.05.14.23.25.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 May 2026 23:25:54 -0700 (PDT) Message-ID: <1a42a168-1dbb-467e-9053-b5585a737f71@gmail.com> Date: Fri, 15 May 2026 14:25:48 +0800 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 2/2] drm/verisilicon: add support for Nuvoton MA35D1 DCUltra Lite display controller To: Icenowy Zheng , maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org Cc: ychuang3@nuvoton.com, schung@nuvoton.com, yclu4@nuvoton.com, dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20260511075142.54752-1-a0987203069@gmail.com> <20260511075142.54752-3-a0987203069@gmail.com> <93e69179dbc495188cfffd8015350b3a55ce7876.camel@iscas.ac.cn> <3b94806073de8bd1d79aa7ec956493f67679e46b.camel@iscas.ac.cn> <4bf6efbb222ebc4d770ad613d17c6185e7cb2fda.camel@iscas.ac.cn> <1d04dd6d-f245-4b83-96b0-c5491fad8093@gmail.com> <76a9e9b676509e85484a1eb31c723b46c7e21a19.camel@iscas.ac.cn> Content-Language: en-US From: Joey Lu In-Reply-To: <76a9e9b676509e85484a1eb31c723b46c7e21a19.camel@iscas.ac.cn> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 5/12/2026 9:12 PM, Icenowy Zheng wrote: > 在 2026-05-12二的 18:59 +0800，Joey Lu写道： >> On 5/12/2026 6:01 PM, Icenowy Zheng wrote: >>> 在 2026-05-12二的 17:06 +0800，Joey Lu写道： >>> >>> ======= 8< ============= >>>>>>>> diff --git a/drivers/gpu/drm/verisilicon/vs_bridge.c >>>>>>>> b/drivers/gpu/drm/verisilicon/vs_bridge.c >>>>>>>> index 7a93049368db..225af322de32 100644 >>>>>>>> --- a/drivers/gpu/drm/verisilicon/vs_bridge.c >>>>>>>> +++ b/drivers/gpu/drm/verisilicon/vs_bridge.c >>>>>>>> @@ -164,13 +164,16 @@ static void >>>>>>>> vs_bridge_enable_common(struct >>>>>>>> vs_crtc *crtc, >>>>>>>>      VSDC_DISP_PANEL_CONFIG_CLK_EN); >>>>>>>>      regmap_set_bits(dc->regs, >>>>>>>> VSDC_DISP_PANEL_CONFIG(output), >>>>>>>>      VSDC_DISP_PANEL_CONFIG_RUNNING); >>>>>>>> - regmap_clear_bits(dc->regs, >>>>>>>> VSDC_DISP_PANEL_START, >>>>>>>> - >>>>>>>> VSDC_DISP_PANEL_START_MULTI_DISP_SYNC); >>>>>>>> - regmap_set_bits(dc->regs, VSDC_DISP_PANEL_START, >>>>>>>> - >>>>>>>> VSDC_DISP_PANEL_START_RUNNING(ou >>>>>>>> tput)); >>>>>>>> >>>>>>>> - regmap_set_bits(dc->regs, >>>>>>>> VSDC_DISP_PANEL_CONFIG_EX(crtc- >>>>>>>>> id), >>>>>>>> - >>>>>>>> VSDC_DISP_PANEL_CONFIG_EX_COMMIT); >>>>>>>> + if (dc->info->has_config_ex) { >>>>>>>> + regmap_clear_bits(dc->regs, >>>>>>>> VSDC_DISP_PANEL_START, >>>>>>>> + >>>>>>>> VSDC_DISP_PANEL_START_MULTI_DISP_SYNC); >>>>>>>> + regmap_set_bits(dc->regs, >>>>>>>> VSDC_DISP_PANEL_START, >>>>>>>> + VSDC_DISP_PANEL_START_RU >>>>>>>> NNIN >>>>>>>> G(ou >>>>>>>> tput >>>>>>>> )); >>>>>>>> + >>>>>>>> + regmap_set_bits(dc->regs, >>>>>>>> VSDC_DISP_PANEL_CONFIG_EX(crtc->id), >>>>>>>> + VSDC_DISP_PANEL_CONFIG_E >>>>>>>> X_CO >>>>>>>> MMIT >>>>>>>> ); >>>>>>> Should the commit operation happen on DC8000/DCUltraLite >>>>>>> too? >>>>>>> (By >>>>>>> writing to DcregFrameBufferConfig0.VALID). >>>>>>> >>>>>>> Many registers written has "Note: This field is double >>>>>>> buffered" in >>>>>>> the >>>>>>> DCUltraLite documentation. >>>>>>> >>>>>>> I suggest create a static function for commit -- write to >>>>>>> the >>>>>>> corresponding commit bit on DC8200, and write to >>>>>>> DcregFrameBufferConfig0.VALID on DC8000/DCUltraLite. >>>>>> [a] There is no commit operation for DCUltra Lite. >>>>>> I'll not add a `VSDC_FB_CONFIG_VALID` macro. VALID (BIT(3)) >>>>>> is a >>>>>> hardware-managed double-buffer status bit: hardware writes >>>>>> 1=PENDING >>>>>> when a new register set is ready and clears to 0=WORKING >>>>>> after >>>>>> the >>>>>> VBLANK copy. Software must never write it, and there is no >>>>>> polling >>>>>> use >>>>> It seems to be writable and controls whether register buffering >>>>> is >>>>> enabled, see [1]. >>>>> >>>>> The description of this bit in MA35D1 TRM says "This ensures a >>>>> frame >>>>> will always start with a valid working set if this register is >>>>> programmed last, which reduces the need for SW to wait for the >>>>> start of >>>>> a VBLANK signal in order to ensure all states are loaded before >>>>> the >>>>> next VBLANK", which indicates some kind of "committing write", >>>>> although >>>>> the code at [1] seems to indicate that double buffering is only >>>>> enabled >>>>> when bit is cleared. >>>>> >>>>> Anyway this bit should be programmable, and "Software must >>>>> never >>>>> write >>>>> it" contradicts with the MA35D1 TRM. >>>>> >>>>> Thanks, >>>>> Icenowy >>>>> >>>>> [1] >>>>> https://github.com/rockos-riscv/rockos-kernel/blob/rockos-v6.6.y/drivers/gpu/drm/eswin/es_dc_hw.c#L993 >>>> Thank you for the correction. I'll add >>>> `#define VSDC_FB_CONFIG_VALID BIT(3)` to vs_primary_plane_regs.h >>>> and >>>> write it in `vs_primary_plane_commit()` for non-config_ex >>>> variants. >>>>>> case in the driver that requires a named constant. For non- >>>>>> config_ex >>>>>> variants, `vs_primary_plane_commit()` performs no commit >>>>>> operation — >>>>>> `VSDC_FB_CONFIG_ENABLE` (OUTPUT, BIT(0)) is set in >>>>>> `vs_crtc_atomic_enable()` and `VSDC_FB_CONFIG_RESET` (BIT(4)) >>>>>> is >>>>>> set/cleared in the bridge enable/disable paths. >>> Well according to the driver code for DC8000 from Eswin, and the >>> bit >>> named "VALID", maybe it should be cleared before programming the >>> registers, and set after programming registers, to make the process >>> of >>> programming registers atomic from the perspective of the display >>> controller. >>> >>> Anyway this should require testing on real hardware to verify. >>> >>> By the way, I see multiple peripheral drivers for MA35D1 get >>> applied in >>> the torvalds tree, but the device tree is still only a skeleton; >>> when >>> will the device tree be updated? >>> >>> Thanks, >>> Icenowy >> Thanks for pointing this out. I’ll perform tests on real hardware >> since >> I haven’t used this bit before. >> >> As for the device tree, we plan to update it comprehensively after >> completing several major IPs, with the goal of releasing the update >> later this year. > Well I bought a MA35D1 board (MYIR MYB-LMA35 + RGB LCD) earlier this > year (and this is where I got the MA35D1 identification register > values). Hope I can have a chance to test this driver by myself. > > As MMC, Ethernet and USB support is all applied, maybe it's already > worthy to update the device tree ;-) > > Thanks, > Icenowy Yes you can! I have performed hardware validation on the MA35D1 and found that this bit acts as a manual latch for the shadow registers rather than an auto-clearing trigger, which clarifies the slightly ambiguous description in the TRM. Following your suggestion, I will align the implementation with ESWIN's DC8000 logic: setting the VALID bit at atomic_begin and clearing it at atomic_flush. My tests confirm this allows the hardware to latch the plane configuration correctly while avoiding the blank screen issues observed with other configurations. I am preparing the v2 patchset with this change, along with the requested commit splits, and will submit it shortly.🙂 >>>>> ========= 8< ========== >>>>>