linux-kernel - Re: [RFC PATCH v3 24/37] kvx: Add memory management

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Message-ID: <Zp5zrkwyagnkoY7F@infradead.org>
Date: Mon, 22 Jul 2024 07:58:54 -0700
From: Christoph Hellwig <hch@...radead.org>
To: ysionneau@...rayinc.com
Cc: linux-kernel@...r.kernel.org, Will Deacon <will@...nel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Jonathan Borne <jborne@...rayinc.com>,
	Julian Vetter <jvetter@...rayinc.com>,
	Clement Leger <clement@...ment-leger.fr>,
	Guillaume Thouvenin <thouveng@...il.com>,
	Jean-Christophe Pince <jcpince@...il.com>,
	Jules Maselbas <jmaselbas@...v.net>,
	Julien Hascoet <jhascoet@...rayinc.com>,
	Louis Morhet <lmorhet@...rayinc.com>,
	Marc Poulhiès <dkm@...aplop.net>,
	Marius Gligor <mgligor@...rayinc.com>,
	Vincent Chardon <vincent.chardon@...ys-design.com>,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	linux-riscv@...ts.infradead.org,
	Robin Murphy <robin.murphy@....com>
Subject: Re: [RFC PATCH v3 24/37] kvx: Add memory management

> +#include "../../../drivers/iommu/dma-iommu.h"

This is not a public header as you can guess from the file path.

> +	switch (dir) {
> +	case DMA_TO_DEVICE:
> +		break;
> +	case DMA_FROM_DEVICE:
> +		break;
> +
> +	case DMA_BIDIRECTIONAL:
> +		inval_dcache_range(paddr, size);

Doing this just for bidirectional is weird unless your architecture
never does any speculative prefetching.  Other architectures
include DMA_FROM_DEVICE here.

> +#ifdef CONFIG_IOMMU_DMA
> +void arch_teardown_dma_ops(struct device *dev)
> +{
> +	dev->dma_ops = NULL;
> +}
> +#endif /* CONFIG_IOMMU_DMA*/

This should not be needed right now.  And will be completley
useless once we do the direct calls to dma-iommu which we plan
to do for Linux 6.12.

> +void arch_setup_dma_ops(struct device *dev, bool coherent)
> +{
> +	dev->dma_coherent = coherent;
> +	if (device_iommu_mapped(dev))
> +		iommu_setup_dma_ops(dev);
> +}

And this seems odd, as iommu_setup_dma_ops is called from the iommu
code and you shouldn't need it here.

I also wonder if we can come up with a way to do the ->dma_coherent
setup in common code and remove a few of these arch hooks entirely.