[U-Boot-Users] [patch] disable caches before booting an app for Blackfin apps

[Mike Frysinger]

On Wednesday 30 January 2008, Rafal Jaworowski wrote:
> Hi Mike,
>
> > It isn't generally save to execute applications outside of U-Boot with
> > caches enabled due to the way the Blackfin processor handles caches
> > (requires software assistance).  This patch disables caches before
> > booting an ELF or just booting raw code.  The previous discussion on the
> > patch was that we wanted to use weaks instead, but that proved to not be
> > feasible when multiple symbols are involved, which puts us back at the
> > ifdef solution.  I've minimized the ugliness by moving the setup step
> > outside of the main function.
> >
> > Signed-off-by: Mike Frysinger <vapier at gentoo.org>
> > ---
> > diff --git a/common/cmd_boot.c b/common/cmd_boot.c
> > index e68f16f..9d4f026 100644
> > --- a/common/cmd_boot.c
> > +++ b/common/cmd_boot.c
> > @@ -32,6 +32,23 @@
> >  DECLARE_GLOBAL_DATA_PTR;
> >  #endif
> >
> > +static inline void go_setup(int argc, char *argv[])
> > +{
> > +#if defined(CONFIG_I386)
> > +	/*
> > +	 * x86 does not use a dedicated register to pass the pointer
> > +	 * to the global_data
> > +	 */
> > +	argv[0] = (char *)gd;
> > +
> > +#elif defined(CONFIG_BLACKFIN)
> > +	if (dcache_status ())
> > +		dcache_disable ();
> > +	if (icache_status ())
> > +		icache_disable ();
> > +#endif
> > +}
> > +
> >  int do_go (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
> >  {
> >  	ulong	addr, rc;
> > @@ -46,25 +63,20 @@ int do_go (cmd_tbl_t *cmdtp, int flag, int argc, char
> > *argv[])
> >
> >  	printf ("## Starting application at 0x%08lX ...\n", addr);
> >
> > +	go_setup(argc, argv);
> > +
> > +#if defined(CONFIG_NIOS)
> >  	/*
> > -	 * pass address parameter as argv[0] (aka command name),
> > -	 * and all remaining args
> > -	 */
> > -#if defined(CONFIG_I386)
> > -	/*
> > -	 * x86 does not use a dedicated register to pass the pointer
> > -	 * to the global_data
> > +	 * Nios function pointers are address >> 1
> >  	 */
> > -	argv[0] = (char *)gd;
> > +	addr >>= 1;
> >  #endif
> > -#if !defined(CONFIG_NIOS)
> > -	rc = ((ulong (*)(int, char *[]))addr) (--argc, &argv[1]);
> > -#else
> > +
> >  	/*
> > -	 * Nios function pointers are address >> 1
> > +	 * pass address parameter as argv[0] (aka command name),
> > +	 * and all remaining args
> >  	 */
> > -	rc = ((ulong (*)(int, char *[]))(addr>>1)) (--argc, &argv[1]);
> > -#endif
> > +	rc = ((ulong (*)(int, char *[]))addr) (--argc, &argv[1]);
> >  	if (rc != 0) rcode = 1;
> >
> >  	printf ("## Application terminated, rc = 0x%lX\n", rc);
> > diff --git a/common/cmd_elf.c b/common/cmd_elf.c
> > index 2eb7453..4683554 100644
> > --- a/common/cmd_elf.c
> > +++ b/common/cmd_elf.c
> > @@ -27,6 +27,21 @@ DECLARE_GLOBAL_DATA_PTR;
> >  #define MAX(a,b) ((a) > (b) ? (a) : (b))
> >  #endif
> >
> > +static inline void bootelf_setup(int argc, char *argv[])
> > +{
> > +	/*
> > +	 * QNX images require the data cache is disabled.
> > +	 * Data cache is already flushed, so just turn it off.
> > +	 */
> > +	if (dcache_status ())
> > +		dcache_disable ();
> > +
>
> Please re-formulate the comment, so it doesn't only refer to QNX, as per
> our recent discussion disabling d-cache before running an external app is
> considered a generic U-Boot operation, not platform specific, see this
> thread:

i dont know anything about the topic.  feel free to submit a follow up patch.  
i merely relocated the existing comment.

> Also, I'm wondering if we shouldn't re-enable the cache after returning
> from an external app (as they are allowed to do so)? Without doing it we
> end up with degraded performance without any notice, require explicit reset
> to return to previous state etc.

i did see that deficiency in the code ... that'd require the code to stay 
inline in the function :/
-mike
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