Re: Relocatable kernel for ppc44x

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Wed, 2011-06-15 at 11:43 +0530, Suzuki Poulose wrote:
> On 06/14/11 17:34, Michal Simek wrote:
> > Hi,
> >
> > have someone tried to support RELOCATABLE kernel on ppc44x?
> As Josh, mentioned, I will be working on this. In fact I was trying a couple of
> patches towards this on PPC440x. But, I am stuck in debugging the hang that I am
> experiencing with the changes. I am setting up a RISCWatch processor probe to
> debug the same.
> 
> Here is some information that I wanted to share :
> 
> The PPC440X currently uses 256M TLB entries to pin the lowmem. When we go for a
> relocatable kernel we have to :
> 
> 1) Restrict the kernel load address to be 256M aligned

Wait a minute ... :-)

There's a difference between having the kernel run from any address and
mapping the linear mapping not starting at 0.

Those are completely orthogonal.

I don't see why off hand you are changing the way the TLB is used. The
only possible change needed is to make sure the initial bolted entry set
by the asm code properly covers the kernel in whatever it's "current"
location is. The rest is a matter of fixing up the relocations...

Cheers,
Ben.

> OR
> 
> 2) Use 16M TLB(the next possible TLB page size supported) entries till the first
> 256M and then use the 256M TLB entries for the rest of lowmem.
> 
> Option 1 is not feasible.
> 
> Towards this, I have tried a patch which uses 16M TLB entries to map the entire
> lowmem on an ebony board. But that doesn't seem to work. I am setting up the JTAG
> to debug the state.
> 
> I have attached the patch below for your reference. Any suggestions/comments would
> be really helpful.
> 
> 
> Thanks
> Suzuki
> 
> ==============================
> 
> 
> Use 16M TLB pages to pin the lowmem on PPC440x.
> 
> ---
>   arch/powerpc/include/asm/mmu-44x.h |    9 +++++++++
>   arch/powerpc/kernel/head_44x.S     |    2 +-
>   arch/powerpc/mm/44x_mmu.c          |    2 +-
>   3 files changed, 11 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6.38.1/arch/powerpc/include/asm/mmu-44x.h
> ===================================================================
> --- linux-2.6.38.1.orig/arch/powerpc/include/asm/mmu-44x.h
> +++ linux-2.6.38.1/arch/powerpc/include/asm/mmu-44x.h
> @@ -121,7 +121,12 @@ typedef struct {
>   #endif
>   
>   /* Size of the TLBs used for pinning in lowmem */
> +#define PPC_PIN_SIZE	(1 << 24)	/* 16M */
> +#define PPC44x_TLB_PIN_SIZE	PPC44x_TLB_16M
> +#if 0
>   #define PPC_PIN_SIZE	(1 << 28)	/* 256M */
> +#define PPC44x_TLB_PIN_SIZE	PPC44x_TLB_256M
> +#endif
>   
>   #if (PAGE_SHIFT == 12)
>   #define PPC44x_TLBE_SIZE	PPC44x_TLB_4K
> @@ -142,7 +147,11 @@ typedef struct {
>   #error "Unsupported PAGE_SIZE"
>   #endif
>   
> +#if 0
>   #define mmu_linear_psize	MMU_PAGE_256M
> +#else
> +#define mmu_linear_psize	MMU_PAGE_16M
> +#endif
>   
>   #define PPC44x_PGD_OFF_SHIFT	(32 - PGDIR_SHIFT + PGD_T_LOG2)
>   #define PPC44x_PGD_OFF_MASK_BIT	(PGDIR_SHIFT - PGD_T_LOG2)
> Index: linux-2.6.38.1/arch/powerpc/kernel/head_44x.S
> ===================================================================
> --- linux-2.6.38.1.orig/arch/powerpc/kernel/head_44x.S
> +++ linux-2.6.38.1/arch/powerpc/kernel/head_44x.S
> @@ -805,7 +805,7 @@ skpinv:	addi	r4,r4,1				/* Increment */
>   
>   	/* pageid fields */
>   	clrrwi	r3,r3,10		/* Mask off the effective page number */
> -	ori	r3,r3,PPC44x_TLB_VALID | PPC44x_TLB_256M
> +	ori	r3,r3,PPC44x_TLB_VALID | PPC44x_TLB_PIN_SIZE
>   
>   	/* xlat fields */
>   	clrrwi	r4,r4,10		/* Mask off the real page number */
> Index: linux-2.6.38.1/arch/powerpc/mm/44x_mmu.c
> ===================================================================
> --- linux-2.6.38.1.orig/arch/powerpc/mm/44x_mmu.c
> +++ linux-2.6.38.1/arch/powerpc/mm/44x_mmu.c
> @@ -84,7 +84,7 @@ static void __init ppc44x_pin_tlb(unsign
>   	: "r" (PPC44x_TLB_SW | PPC44x_TLB_SR | PPC44x_TLB_SX | PPC44x_TLB_G),
>   #endif
>   	  "r" (phys),
> -	  "r" (virt | PPC44x_TLB_VALID | PPC44x_TLB_256M),
> +	  "r" (virt | PPC44x_TLB_VALID | PPC44x_TLB_PIN_SIZE),
>   	  "r" (entry),
>   	  "i" (PPC44x_TLB_PAGEID),
>   	  "i" (PPC44x_TLB_XLAT),
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