linux-kernel - Re: [PATCH v1 05/12] iommu: Introduce get_viommu_size and viommu

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Message-ID: <aEsJKZLRTf36Dh3Q@nvidia.com>
Date: Thu, 12 Jun 2025 10:06:49 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
CC: "jgg@...dia.com" <jgg@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>, "joro@...tes.org"
	<joro@...tes.org>, "ddutile@...hat.com" <ddutile@...hat.com>, "Liu, Yi L"
	<yi.l.liu@...el.com>, "peterz@...radead.org" <peterz@...radead.org>,
	"jsnitsel@...hat.com" <jsnitsel@...hat.com>, "praan@...gle.com"
	<praan@...gle.com>, "linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "iommu@...ts.linux.dev"
	<iommu@...ts.linux.dev>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "patches@...ts.linux.dev"
	<patches@...ts.linux.dev>, "baolu.lu@...ux.intel.com"
	<baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v1 05/12] iommu: Introduce get_viommu_size and
 viommu_init ops

On Thu, Jun 12, 2025 at 08:12:29AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Tuesday, June 10, 2025 1:13 AM
> > + * @get_viommu_size: Get the size of a driver-level vIOMMU structure for a
> > given
> > + *                   @dev corresponding to @viommu_type. Driver should return
> > an
> > + *                   errno if vIOMMU isn't supported accordingly. It is required
> > + *                   for driver to use the VIOMMU_STRUCT_SIZE macro to sanitize
> > + *                   a driver-level vIOMMU structure related to the core one
> 
> What about returning size with '0' indicating NOSUPPORT?

I tend to support other errnos here. Basically this moves all the
driver-level sanity checks from viommu_alloc to get_viommu_size,
to reject an incompatible case immediately before allocating any
structure. And there can be another errno than EOPNOTSUPP.

Thanks
Nicolin