Re: [RFC PATCH v3 6/9] iommu/rockchip: Clear AUTO_GATING bit 1 on the RK356x v1 IOMMU

[Tomeu Vizoso]

On Thu, Jun 4, 2026 at 3:53 PM Midgy BALON <midgy971@xxxxxxxxx> wrote:
>
> On the RK356x v1 IOMMU, RK_MMU_AUTO_GATING resets to 0x3. Bit 1 enables
> auto clock-gating of the page-table walker, so the walker's AXI master
> loses its clock between transactions; a TLB-miss page walk then never
> completes and the IOMMU is left stuck (PAGING_ENABLED, never IDLE).
>
> Clear bit 1 (keeping bit 0, the slave-port gate) once paging is enabled
> so the walker keeps its clock. This is required for the RK3568 NPU MMU.

Hi,

I'm not able to review this patch myself, but maybe it can be
submitted separately while we work on the NPU bits?

Regards,

Tomeu

> Signed-off-by: Midgy BALON <midgy971@xxxxxxxxx>
> ---
>  drivers/iommu/rockchip-iommu.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> index 4da80136933c4..e3d8b6e9ca12b 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c
> @@ -953,6 +953,18 @@ static int rk_iommu_enable(struct rk_iommu *iommu)
>
>         ret = rk_iommu_enable_paging(iommu);
>
> +       if (!ret) {
> +               /*
> +                * RK356x v1 IOMMU: RK_MMU_AUTO_GATING bit 1 enables page-walker
> +                * auto clock-gating; the walker's AXI master then loses its clock
> +                * between transactions and a TLB-miss page walk never completes,
> +                * leaving the IOMMU stuck (PAGING_ENABLED, never IDLE).  Clear
> +                * bit 1 (keep bit 0, the slave-port gate) once paging is enabled.
> +                */
> +               for (i = 0; i < iommu->num_mmu; i++)
> +                       rk_iommu_write(iommu->bases[i], RK_MMU_AUTO_GATING, 0x2);
> +       }
> +
>  out_disable_stall:
>         rk_iommu_disable_stall(iommu);
>  out_disable_clocks:
> --
> 2.39.5
>