Re: [PATCH v2 2/2] ARM: mmu_32: fix setting up zero page when it is in SDRAM

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, May 31, 2023 at 02:40:13PM +0200, Ahmad Fatoum wrote:
> On 31.05.23 14:38, Sascha Hauer wrote:
> > On Wed, May 31, 2023 at 01:58:33PM +0200, Ahmad Fatoum wrote:
> >>> From b6e5c92682467496bd9c57918996f1feffda2dd6 Mon Sep 17 00:00:00 2001
> >>> From: Sascha Hauer <s.hauer@pengutronix.de>
> >>> Date: Wed, 31 May 2023 11:58:51 +0200
> >>> Subject: [PATCH] ARM: mmu_32: fix setting up zero page when it is in SDRAM
> >>>
> >>> We used to skip setting the zero page to faulting when SDRAM starts at
> >>> 0x0. As bootm code now explicitly sets the zero page accessible before
> >>> copying ATAGs there this should no longer be necessary, so
> >>> unconditionally set the zero page to faulting during MMU startup.  This
> >>> also moves the zero page and vector table setup after the point the
> >>> SDRAM has been mapped cachable, because otherwise the zero page and
> >>> possibly the vector table mapping would be overwritten.
> >>>
> >>> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> >>> ---
> >>>  arch/arm/cpu/mmu_32.c | 23 +++++++++--------------
> >>>  1 file changed, 9 insertions(+), 14 deletions(-)
> >>>
> >>> diff --git a/arch/arm/cpu/mmu_32.c b/arch/arm/cpu/mmu_32.c
> >>> index c4e5a3bb0a..14775768a3 100644
> >>> --- a/arch/arm/cpu/mmu_32.c
> >>> +++ b/arch/arm/cpu/mmu_32.c
> >>> @@ -461,19 +461,14 @@ static int set_vector_table(unsigned long adr)
> >>>  
> >>>  static void create_zero_page(void)
> >>
> >> Is this commit incomplete? Vectors should be set up unconditionally and
> >> create_zero_page should be called after it.
> > 
> > Vectors are set up unconditionally and create_zero_page() is called the
> > same way as before.
> 
> So zero page is requested first and then on platforms with vector at
> address 0 requesting fails and we are left without configured IVT?

I think you are misreading the patch. Please look at it again.
create_zero_page() is called only when the vector table is not at 0x0.
It has been like that without this patch, the patch doesn't change
anything here.

Sascha

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