[PATCH 02/10] drm/etnaviv: mmuv2: don't map zero page

[Guido Günther]

Hi Lucas,
On Wed, Dec 19, 2018 at 03:45:38PM +0100, Lucas Stach wrote:
> Keep the page at address 0 as faulting to catch any potential state
> setup issues early.

This is a nice idea! But applying this and making mesa hit that page
leads to the process hanging in D state over here on GC7000:

# [  242.726192] INFO: task kworker/u8:2:37 blocked for more than 120 seconds.
[  242.733010]       Not tainted 4.18.0-00129-gce2b21074b41 #504
[  242.738795] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[  242.746638] kworker/u8:2    D    0    37      2 0x00000028
[  242.752144] Workqueue: events_unbound commit_work
[  242.756860] Call trace:
[  242.759318]  __switch_to+0x94/0xd0
[  242.762741]  __schedule+0x1c0/0x6b8
[  242.766239]  schedule+0x40/0xa8
[  242.769380]  schedule_timeout+0x2f0/0x428
[  242.773410]  dma_fence_default_wait+0x1cc/0x2b8
[  242.777951]  dma_fence_wait_timeout+0x44/0x1b0
[  242.782403]  drm_atomic_helper_wait_for_fences+0x48/0x108
[  242.787819]  commit_tail+0x30/0x80
[  242.791229]  commit_work+0x20/0x30
[  242.794642]  process_one_work+0x1ec/0x458
[  242.798659]  worker_thread+0x48/0x430
[  242.802331]  kthread+0x130/0x138
[  242.805557]  ret_from_fork+0x10/0x1c

This is in dmesg showing that we hit the first page:

    [   65.907388] etnaviv-gpu 38000000.gpu: MMU fault status 0x00000002
    [   65.913497] etnaviv-gpu 38000000.gpu: MMU 0 fault addr 0x00000e40

Without that patch it's sampling random data from that page but does not hang.

Cheers,
 -- Guido

> 
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c b/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
> index f1c88d8ad5ba..f794e04be9e6 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_iommu_v2.c
> @@ -320,8 +320,8 @@ etnaviv_iommuv2_domain_alloc(struct etnaviv_gpu *gpu)
>  	domain = &etnaviv_domain->base;
>  
>  	domain->dev = gpu->dev;
> -	domain->base = 0;
> -	domain->size = (u64)SZ_1G * 4;
> +	domain->base = SZ_4K;
> +	domain->size = (u64)SZ_1G * 4 - SZ_4K;
>  	domain->ops = &etnaviv_iommuv2_ops;
>  
>  	ret = etnaviv_iommuv2_init(etnaviv_domain);
> -- 
> 2.19.1
> 
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