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From: "Christian König" <christian.koenig@amd.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: David1.Zhou@amd.com, intel-gfx@lists.freedesktop.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
	jgg@ziepe.ca, linux-media@vger.kernel.org
Subject: Re: [Intel-gfx] [PATCH 1/6] lib/scatterlist: add sg_set_dma_addr() function
Date: Thu, 12 Mar 2020 11:31:35 +0100	[thread overview]
Message-ID: <b5db44eb-1dde-1671-feb0-9e47d120f172@amd.com> (raw)
In-Reply-To: <20200312101943.GA14618@infradead.org>

Am 12.03.20 um 11:19 schrieb Christoph Hellwig:
> On Thu, Mar 12, 2020 at 11:14:22AM +0100, Christian König wrote:
>>>> The page pointer is set to NULL and only the DMA address,
>>>> length and offset values are valid.
>>> NAK.  The only valid way to fill DMA address in scatterlists is
>>> dma_map_sg / dma_map_sg_attr.
>> How can we then map PCIe BARs into an scatterlist which are not backed by
>> struct pages?
> You can't.  scatterlists by definition map memory backed by a struct
> page.  If you want to map something else struct scatterlist is the
> wrong structure and you need to use something else (which you should
> anyway as struct scatterlist is a bad design patter, and the above
> is only one of the many issues with it).

But how should we then deal with all the existing interfaces which 
already take a scatterlist/sg_table ?

The whole DMA-buf design and a lot of drivers are build around 
scatterlist/sg_table and to me that actually makes quite a lot of sense.

For TTM I'm also trying for quite a while to just nuke the manual 
dma_address arrays we have and switch over to scatterlist/sg_table.

I mean we could come up with a new structure for this, but to me that 
just looks like reinventing the wheel. Especially since drivers need to 
be able to handle both I/O to system memory and I/O to PCIe BARs.

Regards,
Christian.


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  reply	other threads:[~2020-03-12 10:31 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-11 13:51 [Intel-gfx] P2P for DMA-buf Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 1/6] lib/scatterlist: add sg_set_dma_addr() function Christian König
2020-03-11 15:28   ` Christoph Hellwig
2020-03-12 10:14     ` Christian König
2020-03-12 10:19       ` Christoph Hellwig
2020-03-12 10:31         ` Christian König [this message]
2020-03-12 10:47           ` Christoph Hellwig
2020-03-12 11:02             ` Christian König
     [not found]             ` <20200312141928.GK31668@ziepe.ca>
2020-03-12 15:39               ` Christian König
2020-03-12 16:13               ` Logan Gunthorpe
2020-03-13 11:21               ` Christoph Hellwig
2020-03-13 13:33                 ` Christian König
     [not found]                 ` <20200313121742.GZ31668@ziepe.ca>
2020-03-16  8:56                   ` Christoph Hellwig
2020-03-16  9:41                     ` Christian König
2020-03-16  9:52                       ` Christoph Hellwig
2020-03-11 13:51 ` [Intel-gfx] [PATCH 2/6] dma-buf: add peer2peer flag Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 3/6] drm/amdgpu: note that we can handle peer2peer DMA-buf Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 4/6] drm/amdgpu: add checks if DMA-buf P2P is supported Christian König
     [not found]   ` <20200311140415.GB31668@ziepe.ca>
2020-03-11 14:33     ` Christian König
     [not found]       ` <20200311143835.GD31668@ziepe.ca>
2020-03-11 14:43         ` Christian König
2020-03-11 13:51 ` [Intel-gfx] [PATCH 5/6] drm/amdgpu: add support for exporting VRAM using DMA-buf v2 Christian König
2020-03-11 15:08   ` Alex Deucher
2020-03-11 13:51 ` [Intel-gfx] [PATCH 6/6] drm/amdgpu: improve amdgpu_gem_info debugfs file Christian König
2020-03-11 18:09 ` [Intel-gfx] ✗ Fi.CI.CHECKPATCH: warning for series starting with [1/6] lib/scatterlist: add sg_set_dma_addr() function Patchwork
2020-03-11 18:34 ` [Intel-gfx] ✗ Fi.CI.BAT: failure " Patchwork

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