[PATCH] ppc: don't use virtual image stack for startup context

[Mark Cave-Ayland]

Part of commit 070ea60 created a new stack within the virtual image for use by
the startup context. Unfortunately the current implementations of virt_to_phys()
as used by some drivers are incorrect which causes issues with some parts of
OpenBIOS, notably the USB stack.

Revert back to using the initial stack in start.S which ensures a 1:1 mapping
between virtual and physical addresses to avoid such problems.

Signed-off-by: Mark Cave-Ayland 
---
 arch/ppc/qemu/context.c |    1 -
 arch/ppc/qemu/ldscript  |    6 +-----
 arch/ppc/qemu/start.S   |    6 ++++++
 include/arch/ppc/io.h   |    2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/ppc/qemu/context.c b/arch/ppc/qemu/context.c
index 18459b8..65cd4e4 100644
--- a/arch/ppc/qemu/context.c
+++ b/arch/ppc/qemu/context.c
@@ -41,7 +41,6 @@ void of_client_callback(void);
  * to start us up.
  */
 static struct context main_ctx = {
-    .sp = (unsigned long) &_estack - SAVE_SPACE,
     .pc = (unsigned long) start_main,
     .return_addr = (unsigned long) __exit_context,
 };
diff --git a/arch/ppc/qemu/ldscript b/arch/ppc/qemu/ldscript
index 11ebf4b..8027b39 100644
--- a/arch/ppc/qemu/ldscript
+++ b/arch/ppc/qemu/ldscript
@@ -51,11 +51,7 @@ SECTIONS
    *(.bss)
    *(.bss.*)
    *(COMMON)
-	
-	_stack = .;
-	. += CSTACK_SIZE;
-	. = ALIGN(16);
-	_estack = .;
+	_ebss = .;
     }

. = HRESET_ADDR;
diff --git a/arch/ppc/qemu/start.S b/arch/ppc/qemu/start.S
index 33ca1e0..fed1b55 100644
--- a/arch/ppc/qemu/start.S
+++ b/arch/ppc/qemu/start.S
@@ -482,6 +482,12 @@ real_entry:
 #endif

bl	BRANCH_LABEL(setup_mmu)
+
+	/* load stack pointer into context */
+	LOAD_REG_IMMEDIATE(r4, __context)
+	PPC_LL  r4, 0(r4)
+	PPC_STL r1, (2 * ULONG_SIZE)(r4)
+
    bl	BRANCH_LABEL(__switch_context_nosave)
 1:	nop
    b	1b
diff --git a/include/arch/ppc/io.h b/include/arch/ppc/io.h
index 39c60d7..3449c5b 100644
--- a/include/arch/ppc/io.h
+++ b/include/arch/ppc/io.h
@@ -6,7 +6,7 @@
 #define NO_QEMU_PROTOS
 #include "arch/common/fw_cfg.h"

-extern char _start, _end, _estack;
+extern char _start, _end;
 extern unsigned long virt_offset;

#define phys_to_virt(phys) ((void *) ((unsigned long) (phys) - virt_offset))

[Mark Cave-Ayland]

On 22/10/16 11:05, Mark Cave-Ayland wrote:
> Part of commit 070ea60 created a new stack within the virtual image for use by
> the startup context. Unfortunately the current implementations of virt_to_phys()
> as used by some drivers are incorrect which causes issues with some parts of
> OpenBIOS, notably the USB stack.
>
> Revert back to using the initial stack in start.S which ensures a 1:1 mapping
> between virtual and physical addresses to avoid such problems.
> Signed-off-by: Mark Cave-Ayland
>
> arch/ppc/qemu/context.c |    1 -
>  arch/ppc/qemu/ldscript  |    6 +-----
>  arch/ppc/qemu/start.S   |    6 ++++++
>  include/arch/ppc/io.h   |    2 +-
>  4 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/ppc/qemu/context.c b/arch/ppc/qemu/context.c
> index 18459b8..65cd4e4 100644
> --- a/arch/ppc/qemu/context.c
> +++ b/arch/ppc/qemu/context.c
> @@ -41,7 +41,6 @@ void of_client_callback(void);
> to start us up.
>
> */
>  static struct context main_ctx = {
> .sp = (unsigned long) &_estack - SAVE_SPACE,
> .pc = (unsigned long) start_main,
> .return_addr = (unsigned long) __exit_context,
>
> };
> diff --git a/arch/ppc/qemu/ldscript b/arch/ppc/qemu/ldscript
> index 11ebf4b..8027b39 100644
> --- a/arch/ppc/qemu/ldscript
> +++ b/arch/ppc/qemu/ldscript
> @@ -51,11 +51,7 @@ SECTIONS
>    *(.bss)
>    *(.bss.*)
>    *(COMMON)
> _stack = .;
> . += CSTACK_SIZE;
> . = ALIGN(16);
> _estack = .;
>
> _ebss = .;
> }
>
> . = HRESET_ADDR;
>
> diff --git a/arch/ppc/qemu/start.S b/arch/ppc/qemu/start.S
> index 33ca1e0..fed1b55 100644
> --- a/arch/ppc/qemu/start.S
> +++ b/arch/ppc/qemu/start.S
> @@ -482,6 +482,12 @@ real_entry:
>  #endif
>
> bl	BRANCH_LABEL(setup_mmu)
> /* load stack pointer into context */
> LOAD_REG_IMMEDIATE(r4, __context)
> PPC_LL  r4, 0(r4)
> PPC_STL r1, (2 * ULONG_SIZE)(r4)
> bl	BRANCH_LABEL(__switch_context_nosave)
>
> 1:	nop
>    b	1b
> diff --git a/include/arch/ppc/io.h b/include/arch/ppc/io.h
> index 39c60d7..3449c5b 100644
> --- a/include/arch/ppc/io.h
> +++ b/include/arch/ppc/io.h
> @@ -6,7 +6,7 @@
>  #define NO_QEMU_PROTOS
>  #include "arch/common/fw_cfg.h"
>
> -extern char _start, _end, _estack;
> +extern char _start, _end;
>  extern unsigned long virt_offset;
>
> #define phys_to_virt(phys) ((void *) ((unsigned long) (phys) - virt_offset))

I've given this a good test today, and it fixes the USB issue without
introducing any regressions on my PPC boot tests so I've applied this to
master.

ATB,

Mark.