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Date: Fri, 11 Sep 2015 16:33:36 +0100
From: Robin Murphy <robin.murphy@....com>
To: Yong Wu <yong.wu@...iatek.com>, Joerg Roedel <joro@...tes.org>,
Thierry Reding <treding@...dia.com>,
Mark Rutland <Mark.Rutland@....com>,
Matthias Brugger <matthias.bgg@...il.com>
Cc: Will Deacon <Will.Deacon@....com>,
Daniel Kurtz <djkurtz@...gle.com>,
Tomasz Figa <tfiga@...gle.com>,
Lucas Stach <l.stach@...gutronix.de>,
Rob Herring <robh+dt@...nel.org>,
Catalin Marinas <Catalin.Marinas@....com>,
"linux-mediatek@...ts.infradead.org"
<linux-mediatek@...ts.infradead.org>,
Sasha Hauer <kernel@...gutronix.de>,
"srv_heupstream@...iatek.com" <srv_heupstream@...iatek.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
"pebolle@...cali.nl" <pebolle@...cali.nl>,
"arnd@...db.de" <arnd@...db.de>,
"mitchelh@...eaurora.org" <mitchelh@...eaurora.org>,
"youhua.li@...iatek.com" <youhua.li@...iatek.com>,
"k.zhang@...iatek.com" <k.zhang@...iatek.com>,
"frederic.chen@...iatek.com" <frederic.chen@...iatek.com>
Subject: Re: [PATCH v4 5/6] iommu/mediatek: Add mt8173 IOMMU driver
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@...iatek.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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