| Message ID | 57D2E47D.5030105@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 9 Sep 2016, Srinivas Ramana wrote: > Hello, > > While trying to boot arm-32 bit kernel, I came across a problem where TTBCR is > in improper state. If the bootloader uses the long descriptor format and jumps > to kernel decompressor code, TTBCR may not be in the right state. So, as soon > as the MMU is enabled, execution can not proceed further. > > Before enabling the MMU, it is required to clear the TTBCR.PD0 field to use > TTBR0 for translation table walks. Also, TTBCR.N should be reset to '0' to > indicate the correct base address width. The 'commit dbece45894d3a ("ARM: > 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores")' does the reset of > TTBCR.N, but doesn't consider all the bits for the size of TTBCR.N. > > when i tried the below change where i explicitly clear TTBCR.PD0 and use > correct mask for TTBCR.N, I see proper memory after MMU is enabled and > decompression succeeds. > > Request your comments on the change below. If it looks good, I can submit a > patch for inclusion. > > ---------------------8<---------------------------------- > diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S > index af11c2f..5769f1f 100644 > --- a/arch/arm/boot/compressed/head.S > +++ b/arch/arm/boot/compressed/head.S > @@ -779,7 +779,8 @@ __armv7_mmu_cache_on: > orrne r0, r0, #1 @ MMU enabled > movne r1, #0xfffffffd @ domain 0 = client > bic r6, r6, #1 << 31 @ 32-bit translation system > - bic r6, r6, #3 << 0 @ use only ttbr0 > + bic r6, r6, #7 << 0 @ width of base address field > + bic r6, r6, #1 << 4 @ use only ttbr0 You could combine those instructions like this: bic r6, r6, #(7 << 0) | (1 << 4) @ use only ttbr0 Nicolas
On 09/09/2016 11:06 PM, Nicolas Pitre wrote: > On Fri, 9 Sep 2016, Srinivas Ramana wrote: > >> Hello, >> >> While trying to boot arm-32 bit kernel, I came across a problem where TTBCR is >> in improper state. If the bootloader uses the long descriptor format and jumps >> to kernel decompressor code, TTBCR may not be in the right state. So, as soon >> as the MMU is enabled, execution can not proceed further. >> >> Before enabling the MMU, it is required to clear the TTBCR.PD0 field to use >> TTBR0 for translation table walks. Also, TTBCR.N should be reset to '0' to >> indicate the correct base address width. The 'commit dbece45894d3a ("ARM: >> 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores")' does the reset of >> TTBCR.N, but doesn't consider all the bits for the size of TTBCR.N. >> >> when i tried the below change where i explicitly clear TTBCR.PD0 and use >> correct mask for TTBCR.N, I see proper memory after MMU is enabled and >> decompression succeeds. >> >> Request your comments on the change below. If it looks good, I can submit a >> patch for inclusion. >> >> ---------------------8<---------------------------------- >> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S >> index af11c2f..5769f1f 100644 >> --- a/arch/arm/boot/compressed/head.S >> +++ b/arch/arm/boot/compressed/head.S >> @@ -779,7 +779,8 @@ __armv7_mmu_cache_on: >> orrne r0, r0, #1 @ MMU enabled >> movne r1, #0xfffffffd @ domain 0 = client >> bic r6, r6, #1 << 31 @ 32-bit translation system >> - bic r6, r6, #3 << 0 @ use only ttbr0 >> + bic r6, r6, #7 << 0 @ width of base address field >> + bic r6, r6, #1 << 4 @ use only ttbr0 > > You could combine those instructions like this: > > bic r6, r6, #(7 << 0) | (1 << 4) @ use only ttbr0 Sure, Thanks for the suggestion. I can incorporate this and submit a patch. Can i use your Acked-by? Thanks, -- Srinivas R > > Nicolas > -- > To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
On 09/09/2016 11:06 PM, Nicolas Pitre wrote: > On Fri, 9 Sep 2016, Srinivas Ramana wrote: > >> Hello, >> >> While trying to boot arm-32 bit kernel, I came across a problem where TTBCR is >> in improper state. If the bootloader uses the long descriptor format and jumps >> to kernel decompressor code, TTBCR may not be in the right state. So, as soon >> as the MMU is enabled, execution can not proceed further. >> >> Before enabling the MMU, it is required to clear the TTBCR.PD0 field to use >> TTBR0 for translation table walks. Also, TTBCR.N should be reset to '0' to >> indicate the correct base address width. The 'commit dbece45894d3a ("ARM: >> 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores")' does the reset of >> TTBCR.N, but doesn't consider all the bits for the size of TTBCR.N. >> >> when i tried the below change where i explicitly clear TTBCR.PD0 and use >> correct mask for TTBCR.N, I see proper memory after MMU is enabled and >> decompression succeeds. >> >> Request your comments on the change below. If it looks good, I can submit a >> patch for inclusion. >> >> ---------------------8<---------------------------------- >> diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S >> index af11c2f..5769f1f 100644 >> --- a/arch/arm/boot/compressed/head.S >> +++ b/arch/arm/boot/compressed/head.S >> @@ -779,7 +779,8 @@ __armv7_mmu_cache_on: >> orrne r0, r0, #1 @ MMU enabled >> movne r1, #0xfffffffd @ domain 0 = client >> bic r6, r6, #1 << 31 @ 32-bit translation system >> - bic r6, r6, #3 << 0 @ use only ttbr0 >> + bic r6, r6, #7 << 0 @ width of base address field >> + bic r6, r6, #1 << 4 @ use only ttbr0 > > You could combine those instructions like this: > > bic r6, r6, #(7 << 0) | (1 << 4) @ use only ttbr0 Sure, I can do that. Thanks for the suggestion. Will send out a patch for review. Thanks, -- Srinivas R
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S index af11c2f..5769f1f 100644 --- a/arch/arm/boot/compressed/head.S +++ b/arch/arm/boot/compressed/head.S @@ -779,7 +779,8 @@ __armv7_mmu_cache_on: orrne r0, r0, #1 @ MMU enabled movne r1, #0xfffffffd @ domain 0 = client bic r6, r6, #1 << 31 @ 32-bit translation system - bic r6, r6, #3 << 0 @ use only ttbr0 + bic r6, r6, #7 << 0 @ width of base address field + bic r6, r6, #1 << 4 @ use only ttbr0 mcrne p15, 0, r3, c2, c0, 0 @ load page table pointer mcrne p15, 0, r1, c3, c0, 0 @ load domain access
Hello, While trying to boot arm-32 bit kernel, I came across a problem where TTBCR is in improper state. If the bootloader uses the long descriptor format and jumps to kernel decompressor code, TTBCR may not be in the right state. So, as soon as the MMU is enabled, execution can not proceed further. Before enabling the MMU, it is required to clear the TTBCR.PD0 field to use TTBR0 for translation table walks. Also, TTBCR.N should be reset to '0' to indicate the correct base address width. The 'commit dbece45894d3a ("ARM: 7501/1: decompressor: reset ttbcr for VMSA ARMv7 cores")' does the reset of TTBCR.N, but doesn't consider all the bits for the size of TTBCR.N. when i tried the below change where i explicitly clear TTBCR.PD0 and use correct mask for TTBCR.N, I see proper memory after MMU is enabled and decompression succeeds. Request your comments on the change below. If it looks good, I can submit a patch for inclusion. ---------------------8<---------------------------------- control mcrne p15, 0, r6, c2, c0, 2 @ load ttb control ---------------------8<---------------------------------- Thanks, -- Srinivas R