Subject: [RFC 3/4] Misc: SRAM: Hack for allowing executable code in SRAM.

From: [email-masked] (Tony Lindgren)
Date: Wed, 4 Sep 2013 11:06:39 -0700

* Russ Dill <[email-masked]> [130903 09:52]:
> The generic SRAM mechanism does not ioremap memory in a
> manner that allows code to be executed from SRAM. There is
> currently no generic way to request ioremap to return a
> memory area with execution allowed.
> 
> Insert a temporary hack for proof of concept on ARM.
> 
> Signed-off-by: Russ Dill <[email-masked]>
> ---
>  drivers/misc/sram.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
> index 08baaab..e059a23 100644
> --- a/drivers/misc/sram.c
> +++ b/drivers/misc/sram.c
> @@ -31,6 +31,7 @@
>  #include <linux/genalloc.h>
>  #include <linux/sram.h>
>  #include <asm-generic/cacheflush.h>
> +#include <asm/io.h>
>  
>  #define SRAM_GRANULARITY	32
>  
> @@ -138,7 +139,7 @@ static int sram_probe(struct platform_device *pdev)
>  	int ret;
>  
>  	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> -	virt_base = devm_ioremap_resource(&pdev->dev, res);
> +	virt_base = __arm_ioremap_exec(res->start, resource_size(res), false);
>  	if (IS_ERR(virt_base))
>  		return PTR_ERR(virt_base);

You can get rid of this hack by defining ioremap_exec in
include/asm-generic/io.h the same way as ioremap_nocache
is done:

#ifndef ioremap_exec
#define ioremap_exec ioremap
#endif

Then the arch that need ioremap_exec can define and
implement it. Needs to be reviewed on LKML naturally :)

Regards,

Tony