Re: [PATCH] ramoops appears geared to not support ARM

From: Marco Stornelli
Date: Sat Oct 29 2011 - 07:10:36 EST

Il 29/10/2011 11:34, Russell King - ARM Linux ha scritto:
On Sat, Oct 29, 2011 at 10:39:47AM +0200, Marco Stornelli wrote:
(Added linux-arm)

Il 29/10/2011 01:21, Bryan Freed ha scritto:
I had some difficulty in getting ramoops to work on our ARM systems.
The driver maps memory with ioremap() which is supposed to map IO memory,
not physical RAM. This happens to work on x86 and apparently some other
architectures, but it does not work on ARM.
Specifically, I see this comment in __arm_ioremap_pfn_caller():
Don't allow RAM to be mapped - this causes problems with ARMv6+

So here is a patch that hacks around the issue using page_is_ram() to
differentiate between the two.

Am I missing something here?
Is ramoops working on any ARM systems yet, and I am just doing something wrong?

My ARM platform reserves a section of RAM for use by ramoops, but it is still
mapped along with the rest of main memory. This is so /dev/mem can find it
with xlate_dev_mem_ptr().
On x86, I see our BIOS reserves the memory so that it is not counted as main
memory, and it is not mapped until ramoops ioremaps it.

Bryan Freed (1):
ramoops: Add support for ARM systems.

drivers/char/ramoops.c | 67 +++++++++++++++++++++++++++++++++++++----------
1 files changed, 52 insertions(+), 15 deletions(-)

Can some ARM guys give an opinion about that?

Opinion about the patch which isn't present in this email (so we can't
see it) or about the commentry above?

About the ioremap problem. It seems there is a problem on some ARM arch to use ioremap (ramoops driver) to remap a piece of RAM even if it's not used by kernel (reserved at boot with mem option, Bryan can you confirm?). It has been suggested by Bryan to use xlate_dev_mem_ptr(), but I'm not sure if the problem is how to reserve the memory on these ARM archs. I believe ioremap is a general way to do it, of course not using kernel already used by kernel, am I right? Or to be compliant with all archs (in this particular case with ARMv6+) we should use xlate_dev_mem_ptr()?

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