Re: [PATCH] MIPS: reloc: make flush_cache_all() usable

[Antony Pavlov <antonynpavlov@gmail.com>]

On Wed, 26 Jun 2019 08:53:54 +0200
Sascha Hauer <s.hauer@pengutronix.de> wrote:

> Hi Antony,
> 
> On Fri, Jun 21, 2019 at 08:15:07AM +0300, Antony Pavlov wrote:
> > flush_cache_all() uses 'struct cpuinfo_mips current_cpu_data' data fields.
> > These data fields are initialized in r4k_cache_init().
> > 
> > However in the current implementation the r4k_cache_init() function
> > is called __AFTER__ relocate_code().
> > 
> > Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
> > ---
> >  arch/mips/lib/reloc.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/arch/mips/lib/reloc.c b/arch/mips/lib/reloc.c
> > index 14ba6167dd..6f1cd6d82f 100644
> > --- a/arch/mips/lib/reloc.c
> > +++ b/arch/mips/lib/reloc.c
> > @@ -37,6 +37,7 @@
> >  #include <asm/mipsregs.h>
> >  #include <asm/relocs.h>
> >  #include <asm/sections.h>
> > +#include <asm/cpu-features.h>
> >  #include <linux/sizes.h>
> >  #include <asm-generic/memory_layout.h>
> >  
> > @@ -157,6 +158,17 @@ void relocate_code(void *fdt, u32 fdt_size, u32 ram_size)
> >  		apply_reloc(type, (void *)addr, off);
> >  	}
> >  
> > +	/* clear the BSS first */
> > +	memset(__bss_start, 0x00, bss_len);
> > +
> > +	cpu_probe();
> > +
> > +	if (cpu_has_4k_cache) {
> > +		extern void r4k_cache_init(void);
> > +
> > +		r4k_cache_init();
> > +	}
> > +
> >  	/* Ensure the icache is coherent */
> >  	flush_cache_all();
> 
> Can we initialize one field in current_cpu_data to something nonzero so
> that it goes out of the bss?

Or clear only current_cpu_data and keep it in bss?

> Another way would be to pass cpu_probe() a pointer to a struct
> cpuinfo_mips allocated on the stack and then pass it to
> flush_cache_all().
> 
> Clearing the bss twice doesn't look very nice.

It's two diffrent bss segments: one before relocation and one after relocation.

-- 
Best regards,
  Antony Pavlov

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