ARM: dts: fix split memory bank for SSDK5440
Subsystems (2)
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
The size of memory bank should be under 256MB, because current section size is 256MB on EXYNOS SoCs. This patch fixes it.
--- arch/arm/boot/dts/exynos5440-ssdk5440.dts | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
arch/arm/boot/dts/exynos5440-ssdk5440.dts +8 -1
@@ -17,7 +17,14 @@ compatible = "samsung,ssdk5440", "samsung,exynos5440"; memory { - reg = <0x80000000 0x80000000>; + reg = <0x80000000 0x10000000 + 0x90000000 0x10000000 + 0xA0000000 0x10000000 + 0xB0000000 0x10000000 + 0xC0000000 0x10000000 + 0xD0000000 0x10000000 + 0xE0000000 0x10000000 + 0xF0000000 0x10000000>; }; chosen {
Signature · 1 line
1.7.10.4
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Hi,
Quoted 2 lines · Kukjin Kim
The size of memory bank should be under 256MB, because current section size is 256MB on EXYNOS SoCs. This patch fixes it.
This makes no sense. You don't have to split up memory ranges, the code should be made to handle it instead.
What's the actual bug caused by this? The description is vague.
-Olof
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Hi Olof,
Quoted 3 lines · On Thursday 20 of December 2012 11:56:59 Olof Johansson wrote:
Hi,
On Thu, Dec 20, 2012 at 11:03 AM, Kukjin Kim <[email protected]>
Quoted 5 lines · wrote:
Quoted 2 lines
The size of memory bank should be under 256MB, because current section size is 256MB on EXYNOS SoCs. This patch fixes it.
This makes no sense. You don't have to split up memory ranges, the code should be made to handle it instead.
It's not Exynos code which causes the problem. Sparsemem initialization relies on the fact that initial amount of structures to described memory equals to maximum section size which is defined per arch (e.g. ARCH_EXYNOS).
Quoted 1 line
What's the actual bug caused by this? The description is vague.
The kernel panics early on NULL pointer dereference in memory initialization.
Best regards,
Tomasz Figa
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
I would like to ask a question here. Do we need to have sparse even if the physical memory is contiguous? All the recent exynos machines come with physical banks without any holes, and I am thinking why not drop it and use flat mem instead. With LPAE these sections sizes wont be useful, and I dont like to keep different section sizes for different configurations. Any suggestions/opinions are very much helpful to me.
Regards,
Subash
Quoted 31 lines · Tomasz Figa
Hi Olof,
Quoted 3 lines · On Thursday 20 of December 2012 11:56:59 Olof Johansson wrote:
Hi,
On Thu, Dec 20, 2012 at 11:03 AM, Kukjin Kim <[email protected]>
Quoted 5 lines · wrote:
Quoted 2 lines
The size of memory bank should be under 256MB, because current section size is 256MB on EXYNOS SoCs. This patch fixes it.
This makes no sense. You don't have to split up memory ranges, the code should be made to handle it instead.
It's not Exynos code which causes the problem. Sparsemem initialization relies on the fact that initial amount of structures to described memory equals to maximum section size which is defined per arch (e.g.
ARCH_EXYNOS).Quoted 1 line
What's the actual bug caused by this? The description is vague.
The kernel panics early on NULL pointer dereference in memory initialization.
Best regards,
Tomasz Figa--
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PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Hi Subash,
Quoted 6 lines · On Thursday 20 of December 2012 14:19:48 Subash Patel wrote:
I would like to ask a question here. Do we need to have sparse even if the physical memory is contiguous? All the recent exynos machines come with physical banks without any holes, and I am thinking why not drop it and use flat mem instead. With LPAE these sections sizes wont be useful, and I dont like to keep different section sizes for different configurations. Any suggestions/opinions are very much helpful to me.
Since sparse memory is the only option available on Exynos currently in kernel configuration, I assume there was a reason for it. However I am not an expert in memory management, so please correct me if I am wrong.
Best regards,
Tomasz Figa
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Quoted 9 lines · Tomasz Figa
Quoted 6 lines · On Thursday 20 of December 2012 14:19:48 Subash Patel wrote:
I would like to ask a question here. Do we need to have sparse even if the physical memory is contiguous? All the recent exynos machines come with physical banks without any holes, and I am thinking why not drop it and use flat mem instead. With LPAE these sections sizes wont be useful, and I dont like to keep different section sizes for different configurations. Any suggestions/opinions are very much helpful to me.
Quoted 4 lines
Since sparse memory is the only option available on Exynos currently in kernel configuration, I assume there was a reason for it. However I am not an expert in memory management, so please correct me if I am wrong.
Hmm...yeah, as Subash said, it's no problem to disable sparsemem on EXYNOS for now but memory hole can be existing on upcoming EXYNOS such as S5PV210 so keeping sparsemem would be better I think.
- Kukjin
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
In reply to Tomasz FigaQuoted 18 lines · Tomasz Figa
Hi Olof,
Quoted 3 lines · On Thursday 20 of December 2012 11:56:59 Olof Johansson wrote:
Hi,
On Thu, Dec 20, 2012 at 11:03 AM, Kukjin Kim <[email protected]>
Quoted 5 lines · wrote:
Quoted 2 lines
The size of memory bank should be under 256MB, because current section size is 256MB on EXYNOS SoCs. This patch fixes it.
This makes no sense. You don't have to split up memory ranges, the code should be made to handle it instead.
It's not Exynos code which causes the problem. Sparsemem initialization relies on the fact that initial amount of structures to described memory equals to maximum section size which is defined per arch (e.g.
ARCH_EXYNOS).
Quoted 4 lines
Quoted 1 line
What's the actual bug caused by this? The description is vague.
The kernel panics early on NULL pointer dereference in memory initialization.
And of course the debugging information is included in the commit log so that others can see what problem you're experiencing and make a decision whether the proposed solution is the right one...
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Quoted 1 line · Russell King - ARM Linux
[...]
Quoted 6 lines
Quoted 5 lines
Quoted 2 lines
What's the actual bug caused by this? The description is vague.
The kernel panics early on NULL pointer dereference in memory initialization.
(Cc'ed KyongHo Cho)
Yeah, correct. The size of memory bank should be under section size and current section size is 256MiB on EXYNOS. So if we don't change the section size, each memory bank should be under 256MiB. If not, as Tomasz said, kernel panic happens in mem_init().
Quoted 3 lines
And of course the debugging information is included in the commit log so that others can see what problem you're experiencing and make a decision whether the proposed solution is the right one...
Yeah, why not, I will add it in next version.
Thanks.
- Kukjin
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Quoted 12 lines · Kukjin Kim
Quoted 1 line · Russell King - ARM Linux
[...]
Quoted 6 lines
Quoted 5 lines
Quoted 2 lines
What's the actual bug caused by this? The description is vague.
The kernel panics early on NULL pointer dereference in memory initialization.
Quoted 6 lines
(Cc'ed KyongHo Cho)
Yeah, correct. The size of memory bank should be under section size and current section size is 256MiB on EXYNOS. So if we don't change the section size, each memory bank should be under 256MiB. If not, as Tomasz said, kernel panic happens in
mem_init().
That's a bug somewhere, the device tree should describe the hardware, and not necessarily the massaged format that the kernel wants it in to not trigger a bug.
So I don't want to see this patch merged, I want to see a proper fix instead, please.
There are also already other exynos platforms and device trees with more than 256MB in the memory node. Changing all of them this way seems unreasonable.
-Olof
PATCH 1/1 ARM: dts: fix split memory bank for SSDK5440
Quoted 27 lines
From: Olof Johansson [mailto:olof at lixom.net]
Sent: Friday, December 21, 2012 9:36 AMQuoted 12 lines · Kukjin Kim
Quoted 1 line · Russell King - ARM Linux
[...]
Quoted 6 lines
Quoted 5 lines
Quoted 2 lines
What's the actual bug caused by this? The description is vague.
The kernel panics early on NULL pointer dereference in memory initialization.
Quoted 6 lines
(Cc'ed KyongHo Cho)
Yeah, correct. The size of memory bank should be under section size and current section size is 256MiB on EXYNOS. So if we don't change the section size, each memory bank should be under 256MiB. If not, as Tomasz said, kernel panic happens in
mem_init().That's a bug somewhere, the device tree should describe the hardware, and not necessarily the massaged format that the kernel wants it in to not trigger a bug.
Quoted 7 lines
So I don't want to see this patch merged, I want to see a proper fix instead, please.
There are also already other exynos platforms and device trees with more than 256MB in the memory node. Changing all of them this way seems unreasonable.
As Kukjin said earlier, the kernel panic may happen while gathering memory statistics in mem_init()(arch/arm/mm/init.c). Russell King does not agreed to modify mem_init() instead he told that a memory bank must not cross section boundaries.