linux-kernel - Re: [PATCH v2 11/29] iommu/mediatek: Always pm_runtime

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Message-ID: <11fe281d-4873-245b-f506-452900f33d3b@collabora.com>
Date:   Thu, 30 Sep 2021 13:26:07 +0200
From:   Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
To:     Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Evan Green <evgreen@...omium.org>,
        Tomasz Figa <tfiga@...gle.com>,
        Tomasz Figa <tfiga@...omium.org>,
        linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, youlin.pei@...iatek.com,
        Nicolas Boichat <drinkcat@...omium.org>, anan.sun@...iatek.com,
        chao.hao@...iatek.com
Subject: Re: [PATCH v2 11/29] iommu/mediatek: Always pm_runtime_get while tlb
 flush



On 13.08.21 08:53, Yong Wu wrote:
> Prepare for 2 HWs that sharing pgtable in different power-domains.
> 
> The previous SoC don't have PM. Only mt8192 has power-domain,
> and it is display's power-domain which nearly always is enabled.

hi, I see that in mt1873.dtsi, many devices that uses the iommu have the
'power-domains' property.

> 
> When there are 2 M4U HWs, it may has problem.
> In this function, we get the pm_status via the m4u dev, but it don't
> reflect the real power-domain status of the HW since there may be other
> HW also use that power-domain.
> 
> Currently we could not get the real power-domain status, thus always
> pm_runtime_get here.
> 
> Prepare for mt8195, thus, no need fix tags here.
> 
> This patch may drop the performance, we expect the user could
> pm_runtime_get_sync before dma_alloc_attrs which need tlb ops.
> 

Could you explain this sentence a bit? should the user call pm_runtime_get_sync
before calling dma_alloc_attrs?

Thanks,
Dafna

> Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> ---
>   drivers/iommu/mtk_iommu.c | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> index add23a36a5e2..abc721a1da21 100644
> --- a/drivers/iommu/mtk_iommu.c
> +++ b/drivers/iommu/mtk_iommu.c
> @@ -238,8 +238,11 @@ static void mtk_iommu_tlb_flush_range_sync(unsigned long iova, size_t size,
>   
>   	for_each_m4u(data, head) {
>   		if (has_pm) {
> -			if (pm_runtime_get_if_in_use(data->dev) <= 0)
> +			ret = pm_runtime_resume_and_get(data->dev);
> +			if (ret < 0) {
> +				dev_err(data->dev, "tlb flush: pm get fail %d.\n", ret);
>   				continue;
> +			}
>   		}
>   
>   		spin_lock_irqsave(&data->tlb_lock, flags);
>