Subject: Re: [PATCH 1/2] remoteproc: drop memset when loading elf
segments
On Thu 09 Apr 18:29 PDT 2020, Peng Fan wrote:
Hi Bjorn,
Subject: Re: [PATCH 1/2] remoteproc: drop memset when loading elf
segments
On Thu 09 Apr 01:22 PDT 2020, Peng Fan wrote:
To arm64, "dc zva, dst" is used in memset.
Per ARM DDI 0487A.j, chapter C5.3.8 DC ZVA, Data Cache Zero by VA,
"If the memory region being zeroed is any type of Device memory,
this instruction can give an alignment fault which is prioritized
in the same way as other alignment faults that are determined by
the memory type."
On i.MX platforms, when elf is loaded to onchip TCM area, the
region is ioremapped, so "dc zva, dst" will trigger abort.
Since memset is not strictly required, let's drop it.
This would imply that we trust that the firmware doesn't expect
remoteproc to zero out the memory, which we've always done. So I
don't think we can say that it's not required.
Saying an image runs on a remote core needs Linux to help zero out BSS
section, this not make sense to me.
Maybe not, but it has always done it, so if there's firmware out there that
depends on it such change would break them..
My case is as following, I need to load section 7 data.
I no need to let remoteproc to memset section 8/9/10/11/12, the
firmware itself could handle that. Just because the memsz is larger
than filesz, remoreproc must memset?
By having a PT_LOAD segment covering these I think it's reasonable to
assume that the ELF loader should be able to touch the associated memory.
Section Headers:
[Nr] Name Type Addr Off Size
ES Flg Lk Inf Al
[ 0] NULL 00000000 000000
000000 00 0 0 0
[ 1] .interrupts PROGBITS 1ffe0000 010000 000240 00
A 0 0 4
[ 2] .resource_table PROGBITS 1ffe0240 010240 000058 00
A 0 0 1
[ 3] .text PROGBITS 1ffe02a0 0102a0 009ccc 00
AX 0 0 16
[ 4] .ARM ARM_EXIDX 1ffe9f6c 019f6c 000008
00 AL 3 0 4
[ 5] .init_array INIT_ARRAY 1ffe9f74 019f74 000004 04
WA 0 0 4
[ 6] .fini_array FINI_ARRAY 1ffe9f78 019f78 000004 04
WA 0 0 4
[ 7] .data PROGBITS 1fff9240 029240 000084
00 WA 0 0 4
[ 8] .ncache.init PROGBITS 1fff92c4 0292c4 000000 00
W 0 0 1
[ 9] .ncache NOBITS 1fff92c4 0292c4 000a80
00 WA 0 0 4
[10] .bss NOBITS 1fff9d44 0292c4 01f5c0
00 WA 0 0 4
[11] .heap NOBITS 20019304 0292c4 000404
00 WA 0 0 1
[12] .stack NOBITS 20019708 0292c4 000400
00 WA 0 0 1
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
drivers/remoteproc/remoteproc_elf_loader.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/drivers/remoteproc/remoteproc_elf_loader.c
b/drivers/remoteproc/remoteproc_elf_loader.c
index 16e2c496fd45..cc50fe70d50c 100644
--- a/drivers/remoteproc/remoteproc_elf_loader.c
+++ b/drivers/remoteproc/remoteproc_elf_loader.c
@@ -238,14 +238,11 @@ int rproc_elf_load_segments(struct rproc
*rproc,
const struct firmware *fw)
memcpy(ptr, elf_data + offset, filesz);
/*
- * Zero out remaining memory for this segment.
+ * No need zero out remaining memory for this segment.
*
* This isn't strictly required since dma_alloc_coherent already
- * did this for us. albeit harmless, we may consider removing
- * this.
+ * did this for us.
In the case of recovery this comment is wrong, we do not
dma_alloc_coherent() the carveout during a recovery.
Isn't the it the firmware's job to memset the region?
I'm not aware of this being a documented requirement, we've always done it
here for them, so removing this call would be a change in behavior.
And in your case you ioremapped existing TCM, so it's never true.
*/
- if (memsz > filesz)
- memset(ptr + filesz, 0, memsz - filesz);
So I think you do want to zero out this region. Question is how we do it...
I have contacted our M4 owners, we no need clear it from Linux side.
And I think _most_ firmware out there, like yours, does clear BSS etc during
initialization.
We also support booting m4 before booting Linux, at that case, Linux
has noting to do with memset. It is just I try loading m4 image with
Linux, and met the issue that memset trigger abort.
Please see the proposal for attaching to already running remoteproc's from
Mathieu. I don't expect that you want to load your PROGBITS either in this
case?
