Messages in this thread | | | Subject | Re: [PATCH v4 5/6] iommu/mediatek: Add mt8173 IOMMU driver | From | Robin Murphy <> | Date | Fri, 11 Sep 2015 16:33:36 +0100 |
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On 03/08/15 11:21, Yong Wu wrote: > This patch adds support for mediatek m4u (MultiMedia Memory Management > Unit). > > Signed-off-by: Yong Wu <yong.wu@mediatek.com> > --- [...] > +/* > + * There is only one iommu domain called the m4u domain that > + * all Multimedia modules share. > + */ > +static struct mtk_iommu_domain *m4udom;
It's a shame this can't be part of the m4u device's mtk_iommu_data, but since the way iommu_domain_alloc works makes that impossible, I think we have little choice but to use the global and hope your guys never build a system with two of these things in ;)
[...] > +static struct iommu_domain *mtk_iommu_domain_alloc(unsigned type) > +{ > + struct mtk_iommu_domain *priv; > + > + if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA) > + return NULL; > + > + if (m4udom)/* The m4u domain exist. */ > + return &m4udom->domain; > + > + priv = kzalloc(sizeof(*priv), GFP_KERNEL); > + if (!priv) > + return NULL; > + > + priv->domain.geometry.aperture_start = 0; > + priv->domain.geometry.aperture_end = DMA_BIT_MASK(32); > + priv->domain.geometry.force_aperture = true;
My intention is that in the IOMMU_DOMAIN_DMA case you'd call iommu_get_dma_cookie(&priv->domain) here as well, that way I can get rid of some of the dodgy workarounds in arch_setup_dma_ops which try to cover all possible cases (and which I'm now not 100% confident in). I'm just about to start trying to fix that up (expect a repost of my series in a week or two once -rc1 has landed).
> + > + m4udom = priv; > + > + return &priv->domain; > +} [...] > +static int mtk_iommu_add_device(struct device *dev) > +{ > + struct iommu_group *group; > + int ret; > + > + if (!dev->archdata.iommu) /* Not a iommu client device */ > + return -ENODEV; > + > + group = iommu_group_get(dev); > + if (!group) { > + group = iommu_group_alloc(); > + if (IS_ERR(group)) { > + dev_err(dev, "Failed to allocate IOMMU group\n"); > + return PTR_ERR(group); > + } > + } > + > + ret = iommu_group_add_device(group, dev); > + if (ret) { > + dev_err(dev, "Failed to add IOMMU group\n"); > + goto err_group_put; > + }
I know the rest of the code means that you can't hit it in practice, but if you ever did have two client devices in the same group then the iommu_group_get() could legitimately succeed for the second device, then you'd blow up creating a duplicate sysfs entry by adding the device to its own group again. Probably not what you want.
> + > + ret = iommu_attach_group(&m4udom->domain, group); > + if (ret) > + dev_err(dev, "Failed to attach IOMMU group\n");
Similarly here, if two devices did share a group then the group could legitimately already be attached to a domain here (by the first device), so attaching it again would be wrong. I think it would be nicer to check with iommu_get_domain_for_dev() first to see if you need to do anything at all (a valid domain from that implies a valid group).
> + > +err_group_put: > + iommu_group_put(group); > + return ret; > +} [...] > +static int mtk_iommu_probe(struct platform_device *pdev) > +{ > + struct mtk_iommu_data *data; > + struct device *dev = &pdev->dev; > + void __iomem *protect; > + int ret; > + > + data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL); > + if (!data) > + return -ENOMEM; > + > + /* Protect memory. HW will access here while translation fault.*/ > + protect = devm_kzalloc(dev, MTK_PROTECT_PA_ALIGN * 2, GFP_KERNEL); > + if (!protect) > + return -ENOMEM; > + data->protect_base = virt_to_phys(protect); > + > + ret = mtk_iommu_parse_dt(pdev, data); > + if (ret) > + return ret; > + > + if (!m4udom)/* There is no iommu client */ > + return 0;
I don't quite follow this: m4udom is apparently only created by someone calling domain_alloc() - how can you guarantee that happens before this driver is probed? - but if they then go and try to attach the device to their new domain, it's going to end up in mtk_hw_init() poking the hardware of the m4u device that can't have even probed yet.
I can only imagine it currently works by sheer chance due to the horrible arch_setup_dma_ops delayed attachment workaround, so even if I can't remove that completely when I look at it next week I'm liable to change it in a way that breaks this badly ;)
Robin.
> + > + data->dev = dev; > + m4udom->data = data; > + dev_set_drvdata(dev, m4udom); > + > + return 0; > +}
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