* [RFC/RFT][PATCH v2] dma-mapping: set default segment_boundary_mask to ULONG_MAX
@ 2020-04-06 21:06 Nicolin Chen
2020-05-19 8:04 ` Nicolin Chen
0 siblings, 1 reply; 2+ messages in thread
From: Nicolin Chen @ 2020-04-06 21:06 UTC (permalink / raw)
To: robin.murphy, m.szyprowski, hch; +Cc: iommu, linux-kernel
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
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [RFC/RFT][PATCH v2] dma-mapping: set default segment_boundary_mask to ULONG_MAX
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
0 siblings, 0 replies; 2+ messages in thread
From: Nicolin Chen @ 2020-05-19 8:04 UTC (permalink / raw)
To: robin.murphy, m.szyprowski, hch; +Cc: iommu, linux-kernel
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
>
_______________________________________________
iommu mailing list
iommu@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/iommu
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2020-05-19 8:04 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
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 is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).