Re: [PATCH 17/17] iommu/rockchip: disable fetch dte time limit

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Unconditional application of a hardware workaround to all Rockchip IOMMU versions.
--

commit 927dc2f6e4d804f46fcc9640f9c6e784b79d0d3b
Author: Simon Xue <xxm@rock-chips.com>

iommu/rockchip: disable fetch dte time limit

This commit sets bit 31 of the AUTO_GATING IOMMU register to 1 to fix an
issue where the IOMMU blocks after fetching DTE consecutively four times.
It squashes two vendor commits covering RV1126, RK3568, and RK3588 hardware.

> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> index 0013cf196c573..87ae036d64145 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c

[ ... ]

> @@ -948,6 +951,11 @@ static int rk_iommu_enable(struct rk_iommu *iommu)
>  			       rk_ops->mk_dtentries(rk_domain->dt_dma));
>  		rk_iommu_base_command(iommu->bases[i], RK_MMU_CMD_ZAP_CACHE);
>  		rk_iommu_write(iommu->bases[i], RK_MMU_INT_MASK, RK_MMU_IRQ_MASK);
> +
> +		/* Workaround for iommu blocked, BIT(31) default to 1 */
> +		auto_gate = rk_iommu_read(iommu->bases[i], RK_MMU_AUTO_GATING);
> +		auto_gate |= DISABLE_FETCH_DTE_TIME_LIMIT;
> +		rk_iommu_write(iommu->bases[i], RK_MMU_AUTO_GATING, auto_gate);
>  	}

[Severity: High]
The commit message indicates that this issue affects new IOMMU versions
(specifically RV1126, RK3568, and RK3588) and mentions that older versions
do not have this bug.

Does this code apply the workaround unconditionally to all hardware versions
managed by the driver?

If the RK_MMU_AUTO_GATING register is unimplemented, reserved, or has a
different meaning on legacy v1 silicon (such as RK3288 or RK3399), could
reading and writing it trigger an asynchronous bus error or corrupt
undocumented hardware state?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260606-spu-rga3multicore-v1-0-3ec2b15675f7@pengutronix.de?part=17