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.
Maybe just add some NULL check in drm_fbdev_cma_fini?
--
Stefan
>
> Nack.
> -Daniel
>>
>> return 0;
>> done:
>> --
>> 2.10.0
>>
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