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([2a01:e0a:c:37e0:ced3:55bd:f454:e722]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43656b01b7esm15415895e9.13.2024.12.18.02.14.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Dec 2024 02:14:33 -0800 (PST) Message-ID: Date: Wed, 18 Dec 2024 11:14:32 +0100 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 v9 0/6] drm/log: Introduce a new boot logger to draw the kmsg on the screen To: Geert Uytterhoeven Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , John Ogness , Javier Martinez Canillas , "Guilherme G . Piccoli" , bluescreen_avenger@verizon.net, Caleb Connolly , Petr Mladek , Jani Nikula , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Linux-Renesas References: <20241204160014.1171469-1-jfalempe@redhat.com> <301714d8-0723-4881-83e8-24523c121bfe@redhat.com> Content-Language: en-US, fr From: Jocelyn Falempe In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 17/12/2024 15:54, Geert Uytterhoeven wrote: > Hi Jocelyn. > > On Tue, Dec 17, 2024 at 3:46 PM Jocelyn Falempe wrote: >> On 17/12/2024 15:19, Geert Uytterhoeven wrote: >>> On Wed, Dec 4, 2024 at 6:41 PM Jocelyn Falempe wrote: >>>> drm_log is a simple logger that uses the drm_client API to print the kmsg boot log on the screen. >>>> This is not a full replacement to fbcon, as it will only print the kmsg. >>>> It will never handle user input, or a terminal because this is better done in userspace. >>>> >>>> If you're curious on how it looks like, I've put a small demo here: >>>> https://people.redhat.com/jfalempe/drm_log/drm_log_draft_boot_v2.mp4 >>>> >>>> Design decisions: >>>> * It uses the drm_client API, so it should work on all drm drivers from the start. >>>> * It doesn't scroll the message, that way it doesn't need to redraw the whole screen for each new message. >>>> It also means it doesn't have to keep drawn messages in memory, to redraw them when scrolling. >>>> * It uses the new non-blocking console API, so it should work well with PREEMPT_RT >>> >>> I gave this a try on Koelsch (R-Car M2-W), using rcar-du. >>> Unfortunately I don't see any kernel messages, and my monitor complains >>> about no signal. Does this require special support from the driver? >> >> It doesn't require a special support from the driver. But as it is the >> first drm client other than fbdev emulation, I'm not surprised it's >> broken on some driver. >> I know it works on virtio-gpu, nouveau, amdgpu, and even on a OnePlus 6 >> (Qualcomm SDM845/freedreno), without requiring driver changes. >> >> Do you have a serial console on this device, to check if there is >> something in kmsg? > > Nothing interesting to see. Compared to the fbdev client: > > rcar-du feb00000.display: [drm] Registered 2 planes with drm panic > [drm] Initialized rcar-du 1.0.0 for feb00000.display on minor 0 > rcar-du feb00000.display: [drm] Device feb00000.display probed > -Console: switching to colour frame buffer device 240x67 > -rcar-du feb00000.display: [drm] fb0: rcar-dudrmfb frame buffer device > > I did verify (by adding my own debug prints) that the code does > get to the success case in drm_log_register(). > Thanks! Maybe you need to add console=drm_log to your kernel command line, so the kernel will actually use this console. > > Gr{oetje,eeting}s, > > Geert >