linux-kernel - Re: [PATCH 1/3] memory: mediatek: Add a new interface mtk_smi_larb_is

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Date:	Mon, 25 Jul 2016 10:39:52 +0200
From:	Matthias Brugger <matthias.bgg@...il.com>
To:	Yong Wu <yong.wu@...iatek.com>, David Airlie <airlied@...ux.ie>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Hans Verkuil <hans.verkuil@...co.com>
Cc:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Tiffany Lin <tiffany.lin@...iatek.com>,
	Honghui Zhang <honghui.zhang@...iatek.com>,
	Bibby Hsieh <bibby.hsieh@...iatek.com>,
	YT Shen <yt.shen@...iatek.com>, CK Hu <ck.hu@...iatek.com>,
	Daniel Kurtz <djkurtz@...gle.com>,
	Tomasz Figa <tfiga@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Lucas Stach <l.stach@...gutronix.de>, youlin.pei@...iatek.com,
	linux-mediatek@...ts.infradead.org, srv_heupstream@...iatek.com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	iommu@...ts.linux-foundation.org, Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH 1/3] memory: mediatek: Add a new interface
 mtk_smi_larb_is_ready



On 20/07/16 05:01, Yong Wu wrote:
> Currently the iommu consumer always call iommu_present to get whether
> the iommu is ready. But in MTK IOMMU, this function can't indicate
> this. The IOMMU call bus_set_iommu->mtk_iommu_add_device->
> mtk_iommu_attach_device to parse the iommu data, then it's able to
> transfer "struct mtk_smi_iommu" to SMI-LARB, and the iommu uses the
> larbs as compoents, the iommu will finish its probe until all the larbs
> probe done.
>
> If the iommu consumer(like DRM) begin to probe after the time of
> calling bus_set_iommu and before the time of SMI probe finish, it
> will hang like this:
>
> [    7.832359] Call trace:
> [    7.834778] [<ffffffc000764424>] mtk_smi_larb_get+0x24/0xa8
> [    7.840300] [<ffffffc0005a1390>] mtk_drm_crtc_enable+0x6c/0x450
>
> Because the larb->mmu is NULL at that time.
>
> In order to avoid this issue, we add a new interface
> (mtk_smi_larb_is_ready) for checking whether the IOMMU and SMI have
> finished their probe. If it return false, the iommu consumer should
> probe-defer for the IOMMU and SMI.
>

Can't we just skip the functions in the probe and call bus_set_iommu 
only if we were able to bind all components?
Something like this:

diff --git a/drivers/iommu/mtk_iommu.c b/drivers/iommu/mtk_iommu.c
index c3043d8..0bef49b 100644
--- a/drivers/iommu/mtk_iommu.c
+++ b/drivers/iommu/mtk_iommu.c
@@ -649,10 +649,14 @@ static int mtk_iommu_probe(struct platform_device 
*pdev)
         if (ret)
                 return ret;

+       ret = component_master_add_with_match(dev, &mtk_iommu_com_ops, 
match);
+       if (ret)
+               return ret;
+
         if (!iommu_present(&platform_bus_type))
                 bus_set_iommu(&platform_bus_type, &mtk_iommu_ops);

-       return component_master_add_with_match(dev, &mtk_iommu_com_ops, 
match);
+       return ret;
  } 

 

  static int mtk_iommu_remove(struct platform_device *pdev)

Regards,
Matthias