[U-Boot] [PATCH] arm: mxs: Fix vectoring table crafting
The vectoring table has to be placed at 0x0, but U-Boot on MX23/MX28 starts from RAM, so the vectoring table at 0x0 is not present. Craft code that will be placed at 0x0 and will redirect interrupt vectoring to proper location of the U-Boot in RAM.
Signed-off-by: Marek Vasut marex@denx.de CC: Stefano Babic sbabic@denx.de CC: Fabio Estevam fabio.estevam@freescale.com --- arch/arm/cpu/arm926ejs/mxs/mxs.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/arch/arm/cpu/arm926ejs/mxs/mxs.c b/arch/arm/cpu/arm926ejs/mxs/mxs.c index e2b4196..600e2a8 100644 --- a/arch/arm/cpu/arm926ejs/mxs/mxs.c +++ b/arch/arm/cpu/arm926ejs/mxs/mxs.c @@ -139,13 +139,32 @@ int mxs_reset_block(struct mxs_register_32 *reg) return 0; }
+/* + * This function will craft a jumptable at 0x0 which will redirect interrupt + * vectoring to proper location of U-Boot in RAM. + * + * The structure of the jumptable will be as follows: + * ldr pc, [pc, #0x18] ..... for each vector, thus repeated 8 times + * <destination address> ... for each previous ldr, thus also repeated 8 times + * + * The "ldr pc, [pc, #0x18]" instruction above loads address from memory at + * offset 0x18 from current value of PC register. Note that PC is already + * incremented by 4 when computing the offset, so the effective offset is + * actually 0x20, this the associated <destination address>. Loading the PC + * register with an address performs a jump to that address. + */ void mx28_fixup_vt(uint32_t start_addr) { - uint32_t *vt = (uint32_t *)0x20; + /* ldr pc, [pc, #0x18] */ + const uint32_t ldr_pc = 0xe59ff018; + /* Jumptable location is 0x0 */ + uint32_t *vt = (uint32_t *)0x0; int i;
- for (i = 0; i < 8; i++) - vt[i] = start_addr + (4 * i); + for (i = 0; i < 8; i++) { + vt[i] = ldr_pc; + vt[i + 8] = start_addr + (4 * i); + } }
#ifdef CONFIG_ARCH_MISC_INIT
On Thu, Apr 25, 2013 at 11:37 PM, Marek Vasut marex@denx.de wrote:
The vectoring table has to be placed at 0x0, but U-Boot on MX23/MX28 starts from RAM, so the vectoring table at 0x0 is not present. Craft code that will be placed at 0x0 and will redirect interrupt vectoring to proper location of the U-Boot in RAM.
Signed-off-by: Marek Vasut marex@denx.de CC: Stefano Babic sbabic@denx.de CC: Fabio Estevam fabio.estevam@freescale.com
Please always Cc me in 'mxs' patches.
+/*
- This function will craft a jumptable at 0x0 which will redirect interrupt
- vectoring to proper location of U-Boot in RAM.
- The structure of the jumptable will be as follows:
- ldr pc, [pc, #0x18] ..... for each vector, thus repeated 8 times
- <destination address> ... for each previous ldr, thus also repeated 8 times
- The "ldr pc, [pc, #0x18]" instruction above loads address from memory at
- offset 0x18 from current value of PC register. Note that PC is already
- incremented by 4 when computing the offset, so the effective offset is
- actually 0x20, this the associated <destination address>. Loading the PC
- register with an address performs a jump to that address.
- */
I understood what you're doing but not the motivation for it. What problem you're fixing or feature this will allow?
-- Otavio Salvador O.S. Systems E-mail: otavio@ossystems.com.br http://www.ossystems.com.br Mobile: +55 53 9981-7854 http://projetos.ossystems.com.br
Dear Otavio Salvador,
[...]
+/*
- This function will craft a jumptable at 0x0 which will redirect
interrupt + * vectoring to proper location of U-Boot in RAM.
- The structure of the jumptable will be as follows:
- ldr pc, [pc, #0x18] ..... for each vector, thus repeated 8 times
- <destination address> ... for each previous ldr, thus also repeated
8 times + *
- The "ldr pc, [pc, #0x18]" instruction above loads address from memory
at + * offset 0x18 from current value of PC register. Note that PC is already + * incremented by 4 when computing the offset, so the effective offset is + * actually 0x20, this the associated <destination address>. Loading the PC + * register with an address performs a jump to that address.
- */
I understood what you're doing but not the motivation for it. What problem you're fixing or feature this will allow?
In case the CPU core gets and interrupt (data abort, invalid instruction...), the CPU will jump to 0x0. It is imperative for handling code to be present at 0x0, but since U-Boot on MXS is started from RAM, only remnants of SPL are present at 0x0. Any core interrupt will then hit those remnants and cause undefined behavior. This patch puts redirection table there which in turn jumps to U-Boot vectoring entry points in RAM ... but this is all in the commit message already, so dunno if that helps you.
Best regards, Marek Vasut
On Fri, Apr 26, 2013 at 12:10 AM, Marek Vasut marex@denx.de wrote:
Dear Otavio Salvador,
[...]
+/*
- This function will craft a jumptable at 0x0 which will redirect
interrupt + * vectoring to proper location of U-Boot in RAM.
- The structure of the jumptable will be as follows:
- ldr pc, [pc, #0x18] ..... for each vector, thus repeated 8 times
- <destination address> ... for each previous ldr, thus also repeated
8 times + *
- The "ldr pc, [pc, #0x18]" instruction above loads address from memory
at + * offset 0x18 from current value of PC register. Note that PC is already + * incremented by 4 when computing the offset, so the effective offset is + * actually 0x20, this the associated <destination address>. Loading the PC + * register with an address performs a jump to that address.
- */
I understood what you're doing but not the motivation for it. What problem you're fixing or feature this will allow?
In case the CPU core gets and interrupt (data abort, invalid instruction...), the CPU will jump to 0x0. It is imperative for handling code to be present at 0x0, but since U-Boot on MXS is started from RAM, only remnants of SPL are present at 0x0. Any core interrupt will then hit those remnants and cause undefined behavior. This patch puts redirection table there which in turn jumps to U-Boot vectoring entry points in RAM ... but this is all in the commit message already, so dunno if that helps you.
Much clear now. Did you actually tested this in MX23 as well? How did you simulated the exception to test it?
-- Otavio Salvador O.S. Systems E-mail: otavio@ossystems.com.br http://www.ossystems.com.br Mobile: +55 53 9981-7854 http://projetos.ossystems.com.br
Dear Otavio Salvador,
On Fri, Apr 26, 2013 at 12:10 AM, Marek Vasut marex@denx.de wrote:
Dear Otavio Salvador,
[...]
+/*
- This function will craft a jumptable at 0x0 which will redirect
interrupt + * vectoring to proper location of U-Boot in RAM.
- The structure of the jumptable will be as follows:
- ldr pc, [pc, #0x18] ..... for each vector, thus repeated 8 times
- <destination address> ... for each previous ldr, thus also
repeated 8 times + *
- The "ldr pc, [pc, #0x18]" instruction above loads address from
memory at + * offset 0x18 from current value of PC register. Note that PC is already + * incremented by 4 when computing the offset, so the effective offset is + * actually 0x20, this the associated <destination address>. Loading the PC + * register with an address performs a jump to that address.
- */
I understood what you're doing but not the motivation for it. What problem you're fixing or feature this will allow?
In case the CPU core gets and interrupt (data abort, invalid instruction...), the CPU will jump to 0x0. It is imperative for handling code to be present at 0x0, but since U-Boot on MXS is started from RAM, only remnants of SPL are present at 0x0. Any core interrupt will then hit those remnants and cause undefined behavior. This patch puts redirection table there which in turn jumps to U-Boot vectoring entry points in RAM ... but this is all in the commit message already, so dunno if that helps you.
Much clear now. Did you actually tested this in MX23 as well?
No, it is not needed, but you can test it if it'd make you feel better. The ARM core is the same in both, so is the memory map for DRAM and SRAM.
How did you simulated the exception to test it?
Try "md.l 0x1" or "go 0x20", they'll cause either dabt or invalid instruction.
Best regards, Marek Vasut
On Thu, Apr 25, 2013 at 11:37 PM, Marek Vasut marex@denx.de wrote:
The vectoring table has to be placed at 0x0, but U-Boot on MX23/MX28 starts from RAM, so the vectoring table at 0x0 is not present. Craft code that will be placed at 0x0 and will redirect interrupt vectoring to proper location of the U-Boot in RAM.
Signed-off-by: Marek Vasut marex@denx.de CC: Stefano Babic sbabic@denx.de CC: Fabio Estevam fabio.estevam@freescale.com
On a mx23evk:
Tested-by: Fabio Estevam fabio.estevam@freescale.com
On 26/04/2013 04:37, Marek Vasut wrote:
The vectoring table has to be placed at 0x0, but U-Boot on MX23/MX28 starts from RAM, so the vectoring table at 0x0 is not present. Craft code that will be placed at 0x0 and will redirect interrupt vectoring to proper location of the U-Boot in RAM.
Signed-off-by: Marek Vasut marex@denx.de CC: Stefano Babic sbabic@denx.de CC: Fabio Estevam fabio.estevam@freescale.com
Applied to u-boot-imx, thanks.
Best regards, Stefano Babic
participants (4)
-
Fabio Estevam -
Marek Vasut -
Otavio Salvador -
Stefano Babic