On Tue, 2021-08-24 at 15:10 +0800, Hsin-Yi Wang wrote:

On Fri, Aug 13, 2021 at 2:57 PM Yong Wu [off-list ref] wrote:

quoted

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.

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.

Can you check if there are existing users that need to add this
change?

The issue may exist in our most users. Our users mainly are in v4l2.
normally their flow like this:
a) VIDIOC_REQBUFS: call dma_alloc_attrs or dma_buf_map_attachment.
b) VIDIOC_STREAMON. 
c) VIDIOC_QBUF: device_run: pm_runtime_get_sync.

Requesting they call pm_runtime_get before dma_alloc_attrs looks not
reasonable. It seems that they should not care about this.

This patch mainly make sure the flow is right. Locally I have a TODO to
try get the real power-domain status here, the sample code like below:

static struct notifier_block mtk_penpd_notifier;

/* Register the genpd notifier. */
mtk_penpd_notifier.notifier_call = mtk_iommu_pd_callback;
ret = dev_pm_genpd_add_notifier(dev, &mtk_penpd_notifier);

/* Then get the real power domain status in the notifier */
 static int mtk_iommu_pd_callback(struct notifier_block *nb,
                        unsigned long flags, void *data) 
 {
       if (flags == GENPD_NOTIFY_ON)
           /* the real power domain is power on */
       else if (flags == GENPD_NOTIFY_PRE_OFF)
           /* the real power domain are going to power off. Take it as
power off.
            * Skip the tlb ops after receivice this flag.
            */
 }
 
 How about this? or any other suggestion to get the real power-domain
rather than the iommu device's power domain status.
 Thanks.

quoted

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
---

<snip>

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