Re: [PATCH] drm/lima: call drm_mm_init() with a valid allocation range

[Qiang Yu <yuq825@gmail.com>]

On Mon, Jun 1, 2026 at 8:04 PM Henrik Grimler <henrik.grimler@axis.com> wrote:
>
> lima_vm_create() is currently run before va_start and va_end are set up,
> meaning they are both 0. lima_vm_create() runs drm_mm_init() with them
> as arguments for the allocator, and if DRM_DEBUG_MM is enabled the
> DRM_MM_BUG_ON check in drm_mm_init then fires, as seen here on
> exynos4412-odroid-u2:
>
> [    1.736297] ------------[ cut here ]------------
> [    1.740370] kernel BUG at drivers/gpu/drm/drm_mm.c:931!
> [    1.745574] Internal error: Oops - BUG: 0 [#1] SMP ARM
> [    1.750697] Modules linked in:
> [    1.753734] CPU: 0 UID: 0 PID: 41 Comm: kworker/u16:1 Not tainted 7.0.10-postmarketos-exynos4 #11 PREEMPT
> [    1.763372] Hardware name: Samsung Exynos (Flattened Device Tree)
> [    1.769446] Workqueue: events_unbound deferred_probe_work_func
> [    1.775261] PC is at drm_mm_init+0x9c/0xa4
> [    1.779339] LR is at lima_vm_create+0x144/0x17c
> [ ... ]
>
> Fix the issue by moving the lima_vm_create() call after va_start and
> va_end are set up.
>
> Fixes: a1d2a6339961 ("drm/lima: driver for ARM Mali4xx GPUs")
> Signed-off-by: Henrik Grimler <henrik.grimler@axis.com>
> ---
> This is a low priority fix and can wait for v7.2, it does not cause
> any real issues as far as I have seen: drm_mm_init() is re-run some
> seconds after first run with correct parameters.

Reviewed-by: Qiang Yu <yuq825@gmail.com>

drm mm in the empty_vm is not used at all, so no issue caused by it.
drm mm of a real per app vm matters but they are initialized properly
after va_start/end set. In fact only the PDE page matters in empty_vm,
I should only create it instead of the full lima_vm.

> ---
>  drivers/gpu/drm/lima/lima_device.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/lima/lima_device.c b/drivers/gpu/drm/lima/lima_device.c
> index 0bf7105c8748..7c873e62c16d 100644
> --- a/drivers/gpu/drm/lima/lima_device.c
> +++ b/drivers/gpu/drm/lima/lima_device.c
> @@ -368,12 +368,6 @@ int lima_device_init(struct lima_device *ldev)
>         if (err)
>                 goto err_out0;
>
> -       ldev->empty_vm = lima_vm_create(ldev);
> -       if (!ldev->empty_vm) {
> -               err = -ENOMEM;
> -               goto err_out1;
> -       }
> -
>         ldev->va_start = 0;
>         if (ldev->id == lima_gpu_mali450) {
>                 ldev->va_end = LIMA_VA_RESERVE_START;
> @@ -387,6 +381,12 @@ int lima_device_init(struct lima_device *ldev)
>         } else
>                 ldev->va_end = LIMA_VA_RESERVE_END;
>
> +       ldev->empty_vm = lima_vm_create(ldev);
> +       if (!ldev->empty_vm) {
> +               err = -ENOMEM;
> +               goto err_out1;
> +       }
> +
>         ldev->iomem = devm_platform_ioremap_resource(pdev, 0);
>         if (IS_ERR(ldev->iomem)) {
>                 dev_err(ldev->dev, "fail to ioremap iomem\n");
>
> ---
> base-commit: c453c60fdba437f69209e027b418c4a24143605a
> change-id: 20260529-lima-alloc-fix-2cd5408f6493
>
> Best regards,
> --
> Henrik Grimler <henrik.grimler@axis.com>
>