linux-kernel - Re: [PATCH v8 03/12] iommu/mediatek: Add probe_defer for smi-larb

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Date:   Thu, 30 Sep 2021 15:14:45 +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 03/12] iommu/mediatek: Add probe_defer for smi-larb

On Wed, 2021-09-29 at 18:33 +0200, Dafna Hirschfeld wrote:
> 
> On 29.09.21 03:37, Yong Wu wrote:
> > Prepare for adding device_link.
> > 
> > The iommu consumer should use device_link to connect with the
> > smi-larb(supplier). then the smi-larb should run before the iommu
> > consumer. Here we delay the iommu driver until the smi driver is
> > ready,
> > then all the iommu consumers always are after the smi driver.
> > 
> > When there is no this patch, if some consumer drivers run before
> > smi-larb, the supplier link_status is DL_DEV_NO_DRIVER(0) in the
> > device_link_add, then device_links_driver_bound will use WARN_ON
> > to complain that the link_status of supplier is not right.
> > 
> > device_is_bound may be more elegant here. but it is not allowed to
> > EXPORT from https://lore.kernel.org/patchwork/patch/1334670/.
> > 
> > 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    | 2 +-
> >   drivers/iommu/mtk_iommu_v1.c | 2 +-
> >   2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
> > index d837adfd1da5..d5848f78a677 100644
> > --- a/drivers/iommu/mtk_iommu.c
> > +++ b/drivers/iommu/mtk_iommu.c
> > @@ -844,7 +844,7 @@ static int mtk_iommu_probe(struct
> > platform_device *pdev)
> >   			id = i;
> >   
> >   		plarbdev = of_find_device_by_node(larbnode);
> > -		if (!plarbdev) {
> > +		if (!plarbdev || !plarbdev->dev.driver) {
> >   			of_node_put(larbnode);
> >   			return -EPROBE_DEFER;
> 
> if plarbdev is null doesn't that mean that the device does not exist?

This is probe function, Is it possible the platform device is not ready
at this time?

I checked the platform device should be created at:

of_platform_default_populate_init:  arch_initcall_sync
  ->of_platform_populate
      ->of_platform_device_create_pdata

Not sure if this may be delayed for some device. If not, it should be
ENODEV here.

> so we should return -ENODEV in that case?
> 
> thanks,
> Dafna
> 
> >   		}
> > diff --git a/drivers/iommu/mtk_iommu_v1.c
> > b/drivers/iommu/mtk_iommu_v1.c
> > index 1467ba1e4417..4d7809432239 100644
> > --- a/drivers/iommu/mtk_iommu_v1.c
> > +++ b/drivers/iommu/mtk_iommu_v1.c
> > @@ -602,7 +602,7 @@ static int mtk_iommu_probe(struct
> > platform_device *pdev)
> >   		}
> >   
> >   		plarbdev = of_find_device_by_node(larbnode);
> > -		if (!plarbdev) {
> > +		if (!plarbdev || !plarbdev->dev.driver) {
> >   			of_node_put(larbnode);
> >   			return -EPROBE_DEFER;
> >   		}
> > 
> 
> _______________________________________________
> Linux-mediatek mailing list
> Linux-mediatek@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-mediatek

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