Blame libpciaccess-kludge-wc-mmap.patch
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From b30d458202bc0304c705eb081b12ead860584bea Mon Sep 17 00:00:00 2001
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From: Keith Packard <keithp@keithp.com>
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Date: Wed, 16 Apr 2008 19:10:52 +0000
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Subject: Kludge around linux bug and turn off write-through and cache-disable bits
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When mmaping the PCI device, the kernel turns on the write-through and
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cache-disable bits in the allocated PTEs. This disables write-combining mode
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and dramatically reduces write bandwidth to the frame buffer. While that
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should be fixed in the kernel, we'll kludge around it here by using mprotect
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to rewrite the PTEs and get those bits turned off.
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---
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diff --git a/src/linux_sysfs.c b/src/linux_sysfs.c
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index 873dc02..78584d6 100644
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--- a/src/linux_sysfs.c
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+++ b/src/linux_sysfs.c
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@@ -558,6 +558,9 @@ pci_device_linux_sysfs_map_range(struct pci_device *dev,
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strerror(errno), errno);
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/* err = errno;*/
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}
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+ /* KLUDGE ALERT -- rewrite the PTEs to turn off the CD and WT bits */
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+ mprotect (map->memory, map->size, PROT_NONE);
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+ mprotect (map->memory, map->size, PROT_READ|PROT_WRITE);
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}
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#endif
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--
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cgit v0.7.2-37-g538c
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