Re: [PATCH 20/20] iommu: Convert remaining simple drivers to domain_alloc_paging()

From: Jason Gunthorpe <jgg@nvidia.com>
To: Niklas Schnelle <schnelle@linux.ibm.com>
Cc: Andy Gross <agross@kernel.org>,
	Alim Akhtar <alim.akhtar@samsung.com>,
	Bjorn Andersson <andersson@kernel.org>,
	AngeloGioacchino Del Regno 
	<angelogioacchino.delregno@collabora.com>,
	Baolin Wang <baolin.wang@linux.alibaba.com>,
	Gerald Schaefer <gerald.schaefer@linux.ibm.com>,
	Heiko Stuebner <heiko@sntech.de>,
	iommu@lists.linux.dev, Jernej Skrabec <jernej.skrabec@gmail.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Joerg Roedel <joro@8bytes.org>,
	Konrad Dybcio <konrad.dybcio@linaro.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-arm-msm@vger.kernel.org,
	linux-mediatek@lists.infradead.org,
	linux-rockchip@lists.infradead.org, linux-s390@vger.kernel.org,
	linux-samsung-soc@vger.kernel.org, linux-sunxi@lists.linux.dev,
	linux-tegra@vger.kernel.org,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Matthew Rosato <mjrosato@linux.ibm.com>,
	Orson Zhai <orsonzhai@gmail.com>, Rob Clark <robdclark@gmail.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Samuel Holland <samuel@sholland.org>,
	Thierry Reding <thierry.reding@gmail.com>,
	Krishna Reddy <vdumpa@nvidia.com>, Chen-Yu Tsai <wens@csie.org>,
	Will Deacon <will@kernel.org>, Yong Wu <yong.wu@mediatek.com>,
	Chunyan Zhang <zhang.lyra@gmail.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	Kevin Tian <kevin.tian@intel.com>,
	Nicolin Chen <nicolinc@nvidia.com>,
	Steven Price <steven.price@arm.com>
Subject: Re: [PATCH 20/20] iommu: Convert remaining simple drivers to domain_alloc_paging()
Date: Tue, 2 May 2023 12:25:08 -0300	[thread overview]
Message-ID: <ZFErVOr8RDoeZ2tq@nvidia.com> (raw)
In-Reply-To: <b9b6a50724b4f1ac2b98e518a8b9a820a912850f.camel@linux.ibm.com>

On Tue, May 02, 2023 at 04:52:32PM +0200, Niklas Schnelle wrote:
> @@ -1947,7 +1948,7 @@ static struct iommu_domain *__iommu_domain_alloc(struct bus_type *bus,
>         if ((type == IOMMU_DOMAIN_UNMANAGED || type == IOMMU_DOMAIN_DMA) &&
>             bus->iommu_ops->domain_alloc_paging)
>                 domain = bus->iommu_ops->domain_alloc_paging(dev);
> -       else
> +       else if (bus->iommu_ops->domain_alloc)
>                 domain = bus->iommu_ops->domain_alloc(type);
>         if (!domain)
>                 return NULL;

Agh, yes, it should fail, this is right, I'll fold it in, thanks

> This then uses the fallback of an empty IOMMU_DOMAIN_UNMANAGED and I
> get a working device in the guest. Also tried hot unplug where the
> device is taken over by the host again.

Great, thanks, I'll add your tested-by for the s390 drivers.

> I think with my DMA API
> conversion patches we can support blocking domains properly but for a
> temporary solution the above may be acceptable.

Yes, this is a good idea, I encourage all drivers to implement at
least one of BLOCKING or IDENTITY as global static singletons that
can't fail - this will allow us to have cleaner error recovery flows.

Jason