Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941006AbcJRRsp (ORCPT ); Tue, 18 Oct 2016 13:48:45 -0400 Received: from mail.kmu-office.ch ([178.209.48.109]:43485 "EHLO mail.kmu-office.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932230AbcJRRsj (ORCPT ); Tue, 18 Oct 2016 13:48:39 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Tue, 18 Oct 2016 10:42:46 -0700 From: Stefan Agner To: Daniel Vetter Cc: meng.yi@nxp.com, dri-devel@lists.freedesktop.org, jianwei.wang.chn@gmail.com, linux-kernel@vger.kernel.org, alison.wang@freescale.com, Stefan Agner Subject: Re: [PATCH v3 5/5] drm/fsl-dcu: only init fbdev if required In-Reply-To: <20161018074424.GX20761@phenom.ffwll.local> References: <20161017213321.8074-1-stefan@agner.ch> <20161017213321.8074-6-stefan@agner.ch> <20161018074424.GX20761@phenom.ffwll.local> Message-ID: User-Agent: Roundcube Webmail/1.1.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3628 Lines: 107 On 2016-10-18 00:44, Daniel Vetter wrote: > On Mon, Oct 17, 2016 at 02:33:21PM -0700, Stefan Agner wrote: >> There is no need to request a CMA backed framebuffer if fbdev >> emulation is not enabled. >> >> Signed-off-by: Stefan Agner >> --- >> drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c >> index e04efbe..3a5880c 100644 >> --- a/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c >> +++ b/drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c >> @@ -87,7 +87,8 @@ static int fsl_dcu_load(struct drm_device *dev, unsigned long flags) >> goto done; >> dev->irq_enabled = true; >> >> - fsl_dcu_fbdev_init(dev); >> + if (IS_ENABLED(CONFIG_DRM_FBDEV_EMULATION)) >> + fsl_dcu_fbdev_init(dev); > > Totally not required, since this will all no-op out. Also, please nuke > that fsl_dcu_fbdv_init wrapper seems like pointless indirection. Regarding fsl_dcu_fbdev_init wrapper: Fully agreed. That thing was there since inception of that driver, and I always was on the fence of doing it. Will do it for the next merge window! I somehow remembered there was something more to it than just "no need", but I somehow failed to document it in the patch description... So I went back and tested some things without the patch, here is when it blows: Unable to handle kernel NULL pointer dereference at virtual address 000002f0 pgd = cc24c000 [000002f0] *pgd=8c0df831, *pte=00000000, *ppte=00000000 Internal error: Oops: 17 [#1] SMP ARM Modules linked in: CPU: 0 PID: 536 Comm: sh Not tainted 4.9.0-rc1-00001-g4b1532a-dirty #568 Hardware name: Freescale Vybrid VF5xx/VF6xx (Device Tree) task: cc213000 task.stack: cc23e000 PC is at drm_fbdev_cma_fini+0x14/0x5c LR is at fsl_dcu_unload+0x28/0x4c pc : [] lr : [] psr: a0000013 sp : cc23fd80 ip : cc23fd98 fp : cc23fd94 r10: cc1d1e4c r9 : cc23e000 r8 : 00000000 r7 : c0e34888 r6 : 0000000d r5 : 00000000 r4 : ce6ff100 r3 : c0e13b18 r2 : c0e13b18 r1 : 00000110 r0 : ce6ff100 Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none Control: 10c5387d Table: 8c24c04a DAC: 00000051 Process sh (pid: 536, stack limit = 0xcc23e210) Stack: (0xcc23fd80 to 0xcc240000) ... Backtrace: [] (drm_fbdev_cma_fini) from [] (fsl_dcu_unload+0x28/0x4c) r5:ce61e810[ 372.213609] r4:ce61f000 [] (fsl_dcu_unload) from [] (drm_dev_unregister+0x38/0xbc) r5:ce61f000[ 372.228535] r4:ce61f000 ... > > And if there really is an issue with the cma helpers allocating an fb when > they should, then the correct fix is to fix that in the helpers, not in > the drivers. Hm, to safe memory, it would probably be best to do something like: --- a/drivers/gpu/drm/drm_fb_cma_helper.c +++ b/drivers/gpu/drm/drm_fb_cma_helper.c @@ -492,6 +492,9 @@ struct drm_fbdev_cma *drm_fbdev_cma_init_with_funcs(struct drm_device *dev, struct drm_fb_helper *helper; int ret; + if (!drm_fbdev_emulation) + return NULL; + fbdev_cma = kzalloc(sizeof(*fbdev_cma), GFP_KERNEL); if (!fbdev_cma) { dev_err(dev->dev, "Failed to allocate drm fbdev.\n"); But we don't have drm_fbdev_emulation emulation there. Maybe just add some NULL check in drm_fbdev_cma_fini? -- Stefan > > Nack. > -Daniel >> >> return 0; >> done: >> -- >> 2.10.0 >> >> _______________________________________________ >> dri-devel mailing list >> dri-devel@lists.freedesktop.org >> https://lists.freedesktop.org/mailman/listinfo/dri-devel