On Tue, Oct 18, 2016 at 10:42:46AM -0700, Stefan Agner wrote:
> 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 <stefan@xxxxxxxx>
> >> ---
> >> 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 : [<c04cfb20>] lr : [<c04fad74>] 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:
> [<c04cfb0c>] (drm_fbdev_cma_fini) from [<c04fad74>]
> (fsl_dcu_unload+0x28/0x4c)
> r5:ce61e810[ 372.213609] r4:ce61f000
>
> [<c04fad4c>] (fsl_dcu_unload) from [<c04d9550>]
> (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.
Not just that, but you'd leak memory since cma_init always does the
kmalloc of the fbdev_cma struct.
> Maybe just add some NULL check in drm_fbdev_cma_fini?
Probably. I can't read arm-oopses, so no idea what exactly blew up. On a
hunch it's probably drm_fbdev_cma_defio_fini that got things wrong and
needs to check for !fbi || !fbi->defio.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/dri-devel
