linux-kernel - Re: [PATCH v1 4/9] powerpc: Convert to physical address DMA mapping

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Message-ID: <20251004200204.GK3360665@nvidia.com>
Date: Sat, 4 Oct 2025 17:02:04 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Leon Romanovsky <leon@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Leon Romanovsky <leonro@...dia.com>,
	Andreas Larsson <andreas@...sler.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"David S. Miller" <davem@...emloft.net>,
	Geoff Levand <geoff@...radead.org>, Helge Deller <deller@....de>,
	Ingo Molnar <mingo@...hat.com>, iommu@...ts.linux.dev,
	"James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
	Jason Wang <jasowang@...hat.com>, Juergen Gross <jgross@...e.com>,
	linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Matt Turner <mattst88@...il.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Richard Henderson <richard.henderson@...aro.org>,
	sparclinux@...r.kernel.org,
	Stefano Stabellini <sstabellini@...nel.org>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	virtualization@...ts.linux.dev, x86@...nel.org,
	xen-devel@...ts.xenproject.org, Magnus Lindholm <linmag7@...il.com>
Subject: Re: [PATCH v1 4/9] powerpc: Convert to physical address DMA mapping

On Sat, Oct 04, 2025 at 08:19:40AM +0200, Christophe Leroy wrote:
> 
> 
> Le 03/10/2025 à 18:35, Jason Gunthorpe a écrit :
> > On Sun, Sep 28, 2025 at 06:02:24PM +0300, Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro@...dia.com>
> > > 
> > > Adapt PowerPC DMA to use physical addresses in order to prepare code
> > > to removal .map_page and .unmap_page.
> > > 
> > > Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> > > ---
> > >   arch/powerpc/include/asm/iommu.h         |  8 +++---
> > >   arch/powerpc/kernel/dma-iommu.c          | 22 +++++++---------
> > >   arch/powerpc/kernel/iommu.c              | 14 +++++-----
> > >   arch/powerpc/platforms/ps3/system-bus.c  | 33 ++++++++++++++----------
> > >   arch/powerpc/platforms/pseries/ibmebus.c | 15 ++++++-----
> > >   arch/powerpc/platforms/pseries/vio.c     | 21 ++++++++-------
> > >   6 files changed, 60 insertions(+), 53 deletions(-)
> > 
> > I think this is good enough for PPC anything more looks quite hard
> 
> Can you tell what you have in mind ? What more would be interesting to do
> but looks hard ? Maybe it can be a follow-up change ?

The phys_addr_t should be pushed down through the ops function pointer
and only the implementations that need the vaddr should call
virt_to_phys()

Ie try to avoid doing phys -> virt -> phys as it is not efficient.

Jason