Re: [PATCH v4] arm64: errata: Add NXP iMX8QM workaround for A53 cache coherency issue

[Franz Schnyder]

On Mon, Aug 24, 2026 at 12:02:04PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@xxxxxxx>
> 
> According to NXP errata document IMX8_1N94W[1], the i.MX8QuadMax SoC
> suffers from a cache coherency issue (ERR050104). The upper bits, above
> bit 35, of the ARADDR and ACADDR buses within the Arm A53 subsystem
> have been incorrectly connected. This causes some TLBI and IC
> maintenance operations exchanged between the A53 and A72 core clusters
> to be corrupted.
> 
> The workaround requires:
> 
>   - Downgrading targeted TLBI operations to broadcast-all variants.
>     Instead of patching the low-level __TLBI_1 macro (which interferes
>     with the REPEAT_TLBI workaround and causes excessive over-
>     invalidation), redirect high-level TLB flush functions
>     (flush_tlb_mm, __do_flush_tlb_range, flush_tlb_kernel_range,
>     __flush_tlb_kernel_pgtable) to use VMALLE1IS via static key checks.
> 
>   - Upgrading IC IVAU to IC IALLUIS for both kernel (via ALTERNATIVE in
>     invalidate_icache_by_line) and EL0 userspace (via trap-and-upgrade
>     in user_cache_maint_handler with SCTLR_EL1.UCI=0).
> 
>   - Disabling KVM since correct TLB maintenance cannot be guaranteed
>     for guests.
> 
>   - No need to touch SMMU Broadcast TLB Maintenance (BTM) since i.MX8QM
>     does not support broadcast TLB.
> 
> SoC detection uses devicetree compatible string "fsl,imx8qm" or
> "fsl,imx8qp" since the boot CPU MIDR_EL1 (0x410fd034) and AIDR_EL1 (0)
> are not unique to this SoC.
> 
> [1] https://www.nxp.com/docs/en/errata/IMX8_1N94W.pdf

Hi Peng,

I tested this on our HW and the random crashes that occured when both
the A72 and A53 clusters were enabled no longer happen.

Tested-by: Franz Schnyder <franz.schnyder@xxxxxxxxxxx> # Toradex Apalis iMX8QM

Thanks

Franz