From: Nicolin Chen <nicoleotsuka@gmail.com>
To: robin.murphy@arm.com, m.szyprowski@samsung.com, hch@lst.de
Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org
Subject: Re: [RFC/RFT][PATCH v2] dma-mapping: set default segment_boundary_mask to ULONG_MAX
Date: Tue, 19 May 2020 01:04:08 -0700 [thread overview]
Message-ID: <20200519080408.GA15325@Asurada-Nvidia> (raw)
In-Reply-To: <20200406210643.20665-1-nicoleotsuka@gmail.com>
Hi Robin/Christoph,
This v2 was sent a while ago. I know that we had a concern,
yet will we have a closure whether merging it or not?
Thanks!
Nic
On Mon, Apr 06, 2020 at 02:06:43PM -0700, Nicolin Chen wrote:
> The default segment_boundary_mask was set to DMA_BIT_MAKS(32)
> a decade ago by referencing SCSI/block subsystem, as a 32-bit
> mask was good enough for most of the devices.
>
> Now more and more drivers set dma_masks above DMA_BIT_MAKS(32)
> while only a handful of them call dma_set_seg_boundary(). This
> means that most drivers have a 4GB segmention boundary because
> DMA API returns a 32-bit default value, though they might not
> really have such a limit.
>
> The default segment_boundary_mask should mean "no limit" since
> the device doesn't explicitly set the mask. But a 32-bit mask
> certainly limits those devices capable of 32+ bits addressing.
>
> So this patch sets default segment_boundary_mask to ULONG_MAX.
>
> Signed-off-by: Nicolin Chen <nicoleotsuka@gmail.com>
> ---
> Changelog:
> v1->v2
> * Followed Robin's comments to revise the commit message by
> dropping one paragraph of not-entirely-true justification
> (no git-diff level change, so please ack if you tested v1)
>
> include/linux/dma-mapping.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 330ad58fbf4d..ff8cefe85f30 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -736,7 +736,7 @@ static inline unsigned long dma_get_seg_boundary(struct device *dev)
> {
> if (dev->dma_parms && dev->dma_parms->segment_boundary_mask)
> return dev->dma_parms->segment_boundary_mask;
> - return DMA_BIT_MASK(32);
> + return ULONG_MAX;
> }
>
> static inline int dma_set_seg_boundary(struct device *dev, unsigned long mask)
> --
> 2.17.1
>
prev parent reply other threads:[~2020-05-19 8:04 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-06 21:06 [RFC/RFT][PATCH v2] dma-mapping: set default segment_boundary_mask to ULONG_MAX Nicolin Chen
2020-05-19 8:04 ` Nicolin Chen [this message]
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