From: Evan Lavelle <sa212+lkml@cyconix.com>
To: LKML <linux-kernel@vger.kernel.org>
Subject: DMA/PCIe driver: pci_map_sg not merging chunks in the scatterlist?
Date: Thu, 17 Mar 2016 22:09:30 +0000 [thread overview]
Message-ID: <56EB2B1A.8050006@cyconix.com> (raw)
Everything I've read makes me think that pci_map_sg will merge
consecutive physical pages into one scatterlist entry, if possible.
However, this isn't happening on a driver I'm currently writing. The
returned scatterlist contains one entry per page, with the physical
addresses incrementing by 4K per page.
Is this expected behaviour, or do I have to do something to enable
merging? This wouldn't be a major problem, except that the PCIe card I'm
working on only has enough local storage for about 300 scatterlist
entries, which means that DMA ops are limited to a little over 1Mbyte at
a time, which isn't much use.
I'm on x86_64, RHEL6.7, IOMMU not enabled, and I don't need to support
anything prior to 2.6.32. The PCIe card has 32-bit addressing. uname shows:
2.6.32-431.el6.x86_64 #1 SMP x86_64 x86_64 x86_64
Thanks.
reply other threads:[~2016-03-17 22:17 UTC|newest]
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