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Message-ID: <20230720082242.GA6932@lst.de>
Date: Thu, 20 Jul 2023 10:22:42 +0200
From: Christoph Hellwig <hch@....de>
To: Petr Tesařík <petr@...arici.cz>
Cc: Christoph Hellwig <hch@....de>,
Petr Tesarik <petrtesarik@...weicloud.com>,
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Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v4 8/8] swiotlb: search the software IO TLB only if a
device makes use of it
On Thu, Jul 20, 2023 at 10:02:38AM +0200, Petr Tesařík wrote:
> On Thu, 20 Jul 2023 08:47:44 +0200
> Christoph Hellwig <hch@....de> wrote:
>
> > Any reason this can't just do a list_empty_careful on the list
> > instead of adding yet another field that grows struct device?
>
> On which list?
dev->dma_io_tlb_mem->pools?
>
> The dma_io_tlb_pools list only contains transient pools, but a device
> may use bounce buffers from a regular pool.
Oh, true.
> The dma_io_tlb_mem.pools list will always be non-empty, unless the
> system runs without SWIOTLB.
>
> On a system which does have a SWIOTLB, the flag allows to differentiate
> between devices that actually use bounce buffers and devices that do
> not (e.g. because they do not have any addressing limitations).
Ok.
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