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[62.151.111.63]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-436255a0d5dsm13244985e9.27.2024.12.12.03.05.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Dec 2024 03:05:51 -0800 (PST) From: Javier Martinez Canillas To: Simona Vetter , Thomas Zimmermann Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@gmail.com, simona@ffwll.ch, regressions@leemhuis.info, nunojpg@gmail.com, dri-devel@lists.freedesktop.org, regressions@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH] drm/fbdev-dma: Add shadow buffering for deferred I/O In-Reply-To: References: <20241211090643.74250-1-tzimmermann@suse.de> Date: Thu, 12 Dec 2024 12:05:50 +0100 Message-ID: <87jzc5nott.fsf@minerva.mail-host-address-is-not-set> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Simona Vetter writes: > On Wed, Dec 11, 2024 at 10:06:28AM +0100, Thomas Zimmermann wrote: >> DMA areas are not necessarily backed by struct page, so we cannot >> rely on it for deferred I/O. Allocate a shadow buffer for drivers >> that require deferred I/O and use it as framebuffer memory. >>=20 >> Fixes driver errors about being "Unable to handle kernel NULL pointer >> dereference at virtual address" or "Unable to handle kernel paging >> request at virtual address". >>=20 >> The patch splits drm_fbdev_dma_driver_fbdev_probe() in an initial >> allocation, which creates the DMA-backed buffer object, and a tail >> that sets up the fbdev data structures. There is a tail function for >> direct memory mappings and a tail function for deferred I/O with >> the shadow buffer. >>=20 >> It is no longer possible to use deferred I/O without shadow buffer. >> It can be re-added if there exists a reliably test for usable struct >> page in the allocated DMA-backed buffer object. >>=20 >> Signed-off-by: Thomas Zimmermann >> Reported-by: Nuno Gon=C3=A7alves >> CLoses: https://lore.kernel.org/dri-devel/CAEXMXLR55DziAMbv_+2hmLeH-jP96= pmit6nhs6siB22cpQFr9w@mail.gmail.com/ >> Tested-by: Nuno Gon=C3=A7alves >> Fixes: 5ab91447aa13 ("drm/tiny/ili9225: Use fbdev-dma") >> Cc: Thomas Zimmermann >> Cc: # v6.11+ > > fbdev code scares me, but I at least tried to check a few things and looks > all good. > > Reviewed-by: Simona Vetter > Same here, is always scary to review fbdev code but the patch looks good to= me. Reviewed-by: Javier Martinez Canillas --=20 Best regards, Javier Martinez Canillas Core Platforms Red Hat