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

[Chaoyi Chen <chaoyi.chen@rock-chips.com>]

On 6/8/2026 9:45 AM, Chaoyi Chen wrote:
> Hi Midgy,
> 
> On 6/8/2026 5:05 AM, Midgy Balon wrote:
>> Hi Chaoyi,
>>
>>> As I said, it is v2. Could you please try using the code below instead and
>>> see if it works?
>>> [ auto_gate = read(RK_MMU_AUTO_GATING); auto_gate |= BIT(31); write(...) ]
>>
>> Thanks -- that's clearly the right shape (read-modify-write, before paging is
>> enabled, keeping the reset value instead of my clobbering 0x2).
>>
>> I rebuilt v7.1-rc6 (with the rocket RK3568 series + your per-device-ops work)
>> using your bit-31 version and tested it on a ROCK 3B: the NPU IOMMU comes up and
>> services the NPU's DMA cleanly -- the NPU probes, attaches its domain, and runs
>> repeated conv submissions with no DMA_READ_ERROR and no page-walk stall. No
>> regression from the write.
>>
>> To be precise about what I can and can't show: I tested both ways on v7.1-rc6 --
>> with your bit-31 write, and on the reset value (0x3) -- and the NPU
>> IOMMU services
>> the NPU's reads with zero faults in both cases (no DMA_READ_ERROR, no page-walk
>> stall). So I don't have a failing baseline here that bit-31 visibly
>> fixes. Is the
>> AUTO_GATING write needed on current mainline, or only under conditions I'm not
>> reproducing (a particular traffic pattern / silicon rev)? I'll keep the patch in
>> your form unless you'd prefer to drop it.
>>
>> One question so I document it correctly: what does bit 31 of RK_MMU_AUTO_GATING
>> control on the v2 block -- is it a master "disable internal auto clock-gating"
>> for the page-table walker (i.e. so a TLB-miss walk's AXI master keeps its clock
>> to completion)? The RK3568 TRM I have doesn't cover the IOMMU registers, so a
>> one-line description would let me write an accurate comment.
>>
> 
> Glad to hear this works. Please refer to the commit below.
> 
> [0]: https://github.com/rockchip-linux/kernel/commit/7f8158fb41b5cc8e738aaeebc3637c50ebd74cae
> [1]: https://github.com/rockchip-linux/kernel/commit/6a355e5f9a2069a2309e240791bc3aad63b7324e
> 

It looks like RGA needs this patch too, and it has already been merged :).

https://lore.kernel.org/all/20260428-spu-iommudtefix-v2-1-f592f579e508@pengutronix.de/

-- 
Best, 
Chaoyi