Re: [PATCH 1/2] iommu/mediatek: Always tlb_flush_all when each PM resume

[Yong Wu <yong.wu@mediatek.com>]

Hi Dafna,

Sorry for reply late.

On Mon, 2021-11-22 at 12:43 +0200, Dafna Hirschfeld wrote:
> From: Yong Wu <yong.wu@mediatek.com>
> 
> Prepare for 2 HWs that sharing pgtable in different power-domains.
> 
> When there are 2 M4U HWs, it may has problem in the flush_range in
> which
> we get the pm_status via the m4u dev, BUT that function don't reflect
> the
> real power-domain status of the HW since there may be other HW also
> use
> that power-domain.
> 
> The function dma_alloc_attrs help allocate the iommu buffer which
> need the corresponding power domain since tlb flush is needed when
> preparing iova. BUT this function only is for allocating buffer,
> we have no good reason to request the user always call pm_runtime_get
> before calling dma_alloc_xxx. Therefore, we add a tlb_flush_all
> in the pm_runtime_resume to make sure the tlb always is clean.
> 
> Another solution is always call pm_runtime_get in the
> tlb_flush_range.
> This will trigger pm runtime resume/backup so often when the iommu
> power is not active at some time(means user don't call pm_runtime_get
> before calling dma_alloc_xxx), This may cause the performance drop.
> thus we don't use this.
> 
> In other case, the iommu's power should always be active via device
> link with smi.
> 
> The previous SoC don't have PM except mt8192. the mt8192 IOMMU is
> display's
> power-domain which nearly always is enabled. thus no need fix tags
> here.
> Prepare for mt8195.

In this patchset, this message should be not proper. I think you could
add the comment why this patch is needed in mt8173.

> 
> Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> [imporvie inline doc]
> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
> ---
>  drivers/iommu/mtk_iommu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index 25b834104790..28dc4b95b6d9 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -964,6 +964,13 @@ static int __maybe_unused
> mtk_iommu_runtime_resume(struct device *dev)
>  		return ret;
>  	}
>  
> +	/*
> +	 * Users may allocate dma buffer before they call
> pm_runtime_get,
> +	 * in which case it will lack the necessary tlb flush.
> +	 * Thus, make sure to update the tlb after each PM resume.
> +	 */
> +	mtk_iommu_tlb_flush_all(data);

This should not work. since current the *_tlb_flush_all call
pm_runtime_get_if_in_use which will always return 0 when it called from
this runtime_cb in my test. thus, It won't do the tlb_flush_all
actually.

I guess this also depend on these two patches of mt8195 v3.
[PATCH v3 09/33] iommu/mediatek: Remove for_each_m4u in tlb_sync_all
[PATCH v3 10/33] iommu/mediatek: Add tlb_lock in tlb_flush_all

like in [10/33], I added a mtk_iommu_tlb_do_flush_all which don't have
the pm operation.

This looks has a dependence. Let me know if I can help this.

> +
>  	/*
>  	 * Uppon first resume, only enable the clk and return, since
> the values of the
>  	 * registers are not yet set.
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu