Date: Sat, 25 Jul 2026 11:34:11 -0300
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Leon Romanovsky <leon@kernel.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>, iommu@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-coco@lists.linux.dev, Robin Murphy <robin.murphy@arm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Steven Price <steven.price@arm.com>,
	Suzuki K Poulose <Suzuki.Poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
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	Alexey Kardashevskiy <aik@amd.com>,
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	Xu Yilun <yilun.xu@linux.intel.com>, linuxppc-dev@lists.ozlabs.org,
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	stable@vger.kernel.org, Michael Kelley <mhklinux@outlook.com>
Subject: Re: [PATCH v8 01/23] dma-direct: return struct page from
 dma_direct_alloc_from_pool()
Message-ID: <amTJY_CdE-uDgoGG@ziepe.ca>
References: <20260717180442.110954-1-aneesh.kumar@kernel.org>
 <20260717180442.110954-2-aneesh.kumar@kernel.org>
 <20260721115456.GI110966@unreal>
 <yq5atsps77c5.fsf@kernel.org>
 <20260721142921.GN110966@unreal>
 <yq5ao6g0750v.fsf@kernel.org>
 <20260721153321.GO110966@unreal>
 <amEhEKQW0_HJ9cLN@ziepe.ca>
 <20260723075704.GC110966@unreal>
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In-Reply-To: <20260723075704.GC110966@unreal>

On Thu, Jul 23, 2026 at 10:57:04AM +0300, Leon Romanovsky wrote:
> On Wed, Jul 22, 2026 at 04:59:12PM -0300, Jason Gunthorpe wrote:
> > On Tue, Jul 21, 2026 at 06:33:21PM +0300, Leon Romanovsky wrote:
> > 
> > > Something like, but probably void* needs to be phys_addr_t:
> > > 
> > > static inline struct page *dma_phys_to_page(void *addr)
> > > {
> > > #ifdef CONFIG_DMA_DIRECT_REMAP
> > > 	return vmalloc_to_page(addr);
> > > #else
> > > 	return virt_to_page(addr);
> > > #endif
> > > }
> > 
> > I don't like this, we don't know for sure the addr will be in a vmap
> > and this will fail if it isn't.
> 
> Of course we know. The existing "#ifdef CONFIG_DMA_DIRECT_REMAP" is
> relevant for addresses acquired from pool.

Yeah, but I still don't like it :) It is hard to follow if you make
those kinds of leaps, someone will call this new helper on something
they shouldn't

> dma_phys_to_page() is a bad name for some low-level conversion function.
> It needs to be internal to DMA logic, in the level when we convert from
> phys to page.

I think we should not convert from phys to page, that's also easy to
do wrong

Jason