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

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

[Antony Pavlov]

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();
 
-- 
2.20.1


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

[Sascha Hauer]

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?

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.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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

[Antony Pavlov]

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

[Sascha Hauer]

On Fri, Jun 28, 2019 at 11:35:45AM +0300, Antony Pavlov wrote:
> 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?

That would at least make it clear why this is done.

That's important because otherwise some day somebody sends a patch
"mips: remove duplicate clearing of bss" and I might apply it because
it looks correct ;)

There might be one problem with putting current_cpu_data into bss. I
don't know much about MIPS booting, but in case the initial image is
located in some potentially small SRAM then putting current_cpu_data
into bss means that the SRAM has to be big enough for initial image and
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.

Yes, I know, otherwise you could just drop the second bss clearing.

Sascha

-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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