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Date:   Sat, 16 Oct 2021 10:23:27 +0800
From:   Yong Wu <yong.wu@...iatek.com>
To:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        David Airlie <airlied@...ux.ie>,
        "Mauro Carvalho Chehab" <mchehab@...nel.org>
CC:     Evan Green <evgreen@...omium.org>,
        Robin Murphy <robin.murphy@....com>,
        Tomasz Figa <tfiga@...omium.org>,
        Will Deacon <will.deacon@....com>,
        <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>,
        Matthias Kaehlcke <mka@...omium.org>, <anan.sun@...iatek.com>,
        <yi.kuo@...iatek.com>, <acourbot@...omium.org>,
        <linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        "Daniel Vetter" <daniel@...ll.ch>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        "Philipp Zabel" <p.zabel@...gutronix.de>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Hsin-Yi Wang <hsinyi@...omium.org>,
        Eizan Miyamoto <eizan@...omium.org>,
        <anthony.huang@...iatek.com>,
        Frank Wunderlich <frank-w@...lic-files.de>
Subject: Re: [PATCH v8 04/12] iommu/mediatek: Add device_link between the
 consumer and the larb devices

On Mon, 2021-10-11 at 14:36 +0200, Dafna Hirschfeld wrote:
> 
> On 29.09.21 03:37, Yong Wu wrote:
> > MediaTek IOMMU-SMI diagram is like below. all the consumer connect
> > with
> > smi-larb, then connect with smi-common.
> > 
> >          M4U
> >           |
> >      smi-common
> >           |
> >    -------------
> >    |         |    ...
> >    |         |
> > larb1     larb2
> >    |         |
> > vdec       venc
> > 
> > When the consumer works, it should enable the smi-larb's power
> > which
> > also need enable the smi-common's power firstly.
> > 
> > Thus, First of all, use the device link connect the consumer and
> > the
> > smi-larbs. then add device link between the smi-larb and smi-
> > common.
> > 
> > This patch adds device_link between the consumer and the larbs.
> > 
> > When device_link_add, I add the flag DL_FLAG_STATELESS to avoid
> > calling
> > pm_runtime_xx to keep the original status of clocks. It can avoid
> > two
> > issues:
> > 1) Display HW show fastlogo abnormally reported in [1]. At the
> > beggining,
> > all the clocks are enabled before entering kernel, but the clocks
> > for
> > display HW(always in larb0) will be gated after clk_enable and
> > clk_disable
> > called from device_link_add(->pm_runtime_resume) and rpm_idle. The
> > clock
> > operation happened before display driver probe. At that time, the
> > display
> > HW will be abnormal.
> > 
> > 2) A deadlock issue reported in [2]. Use DL_FLAG_STATELESS to skip
> > pm_runtime_xx to avoid the deadlock.
> > 
> > Corresponding, DL_FLAG_AUTOREMOVE_CONSUMER can't be added, then
> > device_link_removed should be added explicitly.
> > 
> > [1] 
> > https://lore.kernel.org/linux-mediatek/1564213888.22908.4.camel@mhfsdcap03/
> > [2] https://lore.kernel.org/patchwork/patch/1086569/
> > 
> > Suggested-by: Tomasz Figa <tfiga@...omium.org>
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > Tested-by: Frank Wunderlich <frank-w@...lic-files.de> # BPI-
> > R2/MT7623
> > ---
> >   drivers/iommu/mtk_iommu.c    | 22 ++++++++++++++++++++++
> >   drivers/iommu/mtk_iommu_v1.c | 20 +++++++++++++++++++-
> >   2 files changed, 41 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index d5848f78a677..a2fa55899434 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -560,22 +560,44 @@ static struct iommu_device
> > *mtk_iommu_probe_device(struct device *dev)
> >   {
> >   	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> >   	struct mtk_iommu_data *data;
> > +	struct device_link *link;
> > +	struct device *larbdev;
> > +	unsigned int larbid;
> >   
> >   	if (!fwspec || fwspec->ops != &mtk_iommu_ops)
> >   		return ERR_PTR(-ENODEV); /* Not a iommu client device
> > */
> >   
> >   	data = dev_iommu_priv_get(dev);
> >   
> > +	/*
> > +	 * Link the consumer device with the smi-larb device(supplier)
> > +	 * The device in each a larb is a independent HW. thus only
> > link
> > +	 * one larb here.
> > +	 */
> > +	larbid = MTK_M4U_TO_LARB(fwspec->ids[0]);
> 
> so larbid is always the same for all the ids of a device? 

Yes. For me, each a dtsi node should represent a HW unit which can only
connect one larb.

> If so maybe it worth testing it and return error if this is not the
> case.

Thanks for the suggestion. This is very helpful. I did see someone put
the different larbs in one node. I will check this, and add return
EINVAL for this case.

> 
> Thanks,
> Dafna
 
> > 

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