Messages in this thread | | | Date | Sat, 9 Oct 2010 14:52:11 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH] ARM: allow, but warn, when issuing ioremap() on RAM |
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On Thu, Oct 07, 2010 at 12:44:22PM +0300, Felipe Contreras wrote: > For issues related to this: > http://article.gmane.org/gmane.linux.ports.arm.kernel/84454
This one nicely shows some of the problems which can occur with the memory type attributes - and this is not attributable to ioremap().
ioremap() is used to map devices. It creates device memory type mappings. If what you're mapping doesn't support device memory type mappings, then accesses via an ioremap()'d region isn't going to work - as this guy is observing.
That's not because ioremap() is doing something wrong. It's doing what it's meant to do. The use is wrong, and is completely unrelated to the issue you've raised.
> http://article.gmane.org/gmane.linux.ports.sh.devel/8560
This one we know about, and as I've already said, it ends up with three aliasing mappings each with different attributes thusly:
cpu = dma_alloc_coherent(dev, size, &dma, GFP_KERNEL); dma_declare_coherent_memory(dev, dma, dma, size, DMA_MEMORY_MAP); ==> ioremap(dma, size); ... dma_alloc_coherent(dev, ...);
This wasn't spotted in the review of sh-mobile code because it's not part of the sh-mobile code base, but some of the generic sh architecture code. sh-mobile went into the kernel on March 12th, so it does pre-date the change to ioremap, and is therefore technically a regression.
However, as can be seen from the link above, it's been known about since 8th August - two months ago. The problem has been discussed, and we had a good solution which would work. But then an oar got thrown in which basically resulted in that solution being rejected - on the basis that "it's an established API and it must work".
Well, this usage of the API doesn't work on x86!
The result - progress on the issue hit a brick wall and is unable to proceed because of personal viewpoints conflicting with reality.
> http://www.spinics.net/lists/linux-fbdev/msg01745.html
External user? Unreviewed code? You can't seriously be suggesting that we should care about code we haven't seen which is sitting externally to the kernel tree, and this is a valid reason to hold off on changes to the kernel.
> http://article.gmane.org/gmane.linux.drivers.video-input-infrastructure/22271
"No file".
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