linux-kernel - Re: [PATCH v1 3/9] parisc: Convert DMA map_page to map

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Message-ID: <20251003150144.GC3360665@nvidia.com>
Date: Fri, 3 Oct 2025 12:01:44 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Leon Romanovsky <leon@...nel.org>
Cc: 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 3/9] parisc: Convert DMA map_page to map_phys interface

On Sun, Sep 28, 2025 at 06:02:23PM +0300, Leon Romanovsky wrote:
> +ccio_map_phys(struct device *dev, phys_addr_t phys, size_t size,
> +	      enum dma_data_direction direction, unsigned long attrs)
>  {
> -	return ccio_map_single(dev, page_address(page) + offset, size,
> -			direction);
> +	if (attrs & DMA_ATTR_MMIO)
> +		return DMA_MAPPING_ERROR;
> +
> +	return ccio_map_single(dev, phys_to_virt(phys), size, direction);

This doesn't actually use the virt at all:

	offset = ((unsigned long) addr) & ~IOVP_MASK;
	if((size % L1_CACHE_BYTES) || ((unsigned long)addr % L1_CACHE_BYTES))
		ccio_io_pdir_entry(pdir_start, KERNEL_SPACE, (unsigned long)addr, hint);

And ccio_io_pdir_entry():
	pa = lpa(vba);

Is a special instruction that uses virt but AI tells me that special
LPA instruction is returning phys. Not sure if that is a different
value than virt_to_phys()..

IDK, I'm not feeling brave enough to drop the LPA but maybe include
this note in the commit message.

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason