What to do with rtems_cache_disable_data()?

[Sebastian Huber]

On 14.06.24 11:47, Sebastian Huber wrote:
> Hello,
> 
> an user noticed that for example on the Xilinx Zynq 7000 BSP, the 
> rtems_cache_disable_data() doesn't work.
> 
> I had a look at this and managed to disable the L1 and L2 caches, 
> however, afterwards I got not that far. On the Cortex-A cores it seems 
> at least the L1 data cache is required to provide support for atomic 
> operations:
> 
> https://stackoverflow.com/questions/76207164/disabled-dcache-will-prevent-atomic-flag-from-being-set
> 
> I guess we have this situation on most modern chips with caches since 
> the reservation granule is usually a cache line. How do we want to deal 
> with rtems_cache_disable_data() in this case? From my point of view, 
> this function as no real use case and adding it in the first place was a 
> mistake.
> 
> We have a couple of options:
> 
> * Make the rtems_cache_disable_data() directive a no-operation. 
> Afterwards the cache is still enabled, and an user may get confused.
> 
> * Issue a fatal error if someone calls rtems_cache_disable_data().
> 
> * Really disable the cache and let the user figure out that the atomic 
> operations no longer work. Disabling the data cache can be a quite 
> complex thing to do.
> 
> * Add a return status code to rtems_cache_disable_data() and let it 
> return RTEMS_UNSATISFIED for example.

Removing the ability to disable the data cache leads to further issues. 
Since in this case I am no longer able to test the 
rtems_cache_invalidate_entire_data() function. So, if you cannot disable 
the data cache, then invalidating the entire data cache needs to be a 
fatal error also.

-- 
embedded brains GmbH & Co. KG
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber at embedded-brains.de
phone: +49-89-18 94 741 - 16
fax:   +49-89-18 94 741 - 08

Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/