linux-kernel - Re: [PATCH 02/10] PCI/P2PDMA: Introduce p2pdma_provider structure for cleaner abstraction

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Message-ID: <20250724075533.GR402218@unreal>
Date: Thu, 24 Jul 2025 10:55:33 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Alex Williamson <alex.williamson@...hat.com>,
	Jason Gunthorpe <jgg@...dia.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Christian König <christian.koenig@....com>,
	dri-devel@...ts.freedesktop.org, iommu@...ts.linux.dev,
	Jens Axboe <axboe@...nel.dk>,
	Jérôme Glisse <jglisse@...hat.com>,
	Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	linux-mm@...ck.org, linux-pci@...r.kernel.org,
	Logan Gunthorpe <logang@...tatee.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Vivek Kasireddy <vivek.kasireddy@...el.com>,
	Will Deacon <will@...nel.org>
Subject: Re: [PATCH 02/10] PCI/P2PDMA: Introduce p2pdma_provider structure
 for cleaner abstraction

On Thu, Jul 24, 2025 at 09:51:45AM +0200, Christoph Hellwig wrote:
> On Wed, Jul 23, 2025 at 04:00:03PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...dia.com>
> > 
> > Extract the core P2PDMA provider information (device owner and bus
> > offset) from the dev_pagemap into a dedicated p2pdma_provider structure.
> > This creates a cleaner separation between the memory management layer and
> > the P2PDMA functionality.
> > 
> > The new p2pdma_provider structure contains:
> > - owner: pointer to the providing device
> > - bus_offset: computed offset for non-host transactions
> > 
> > This refactoring simplifies the P2PDMA state management by removing
> > the need to access pgmap internals directly. The pci_p2pdma_map_state
> > now stores a pointer to the provider instead of the pgmap, making
> > the API more explicit and easier to understand.
> 
> I really don't see how anything becomes cleaner or simpler here.
> It adds a new structure that only exists embedded in the exist one
> and more code for no apparent benefit.

Please, see last patch in the series https://lore.kernel.org/all/aea452cc27ca9e5169f7279d7b524190c39e7260.1753274085.git.leonro@nvidia.com
It gives me a way to call p2p code with stable pointer for whole BAR.

Thanks

> 
>