[U-Boot] [PATCH v9 12/18] sandbox: Enhance map_to_sysmem() to handle foreign pointers

[Simon Glass]

Hi Alex,

On 26 August 2018 at 19:11, Alexander Graf <agraf at suse.de> wrote:
>
>
> On 08.08.18 11:54, Simon Glass wrote:
>> At present map_sysmem() maps an address into the sandbox RAM buffer,
>> return a pointer, while map_to_sysmem() goes the other way.
>>
>> The mapping is currently just 1:1 since a case was not found where a more
>> flexible mapping was needed. PCI does have a separate and more complex
>> mapping, but uses its own mechanism.
>>
>> However this arrange cannot handle one important case, which is where a
>> test declares a stack variable and passes a pointer to it into a U-Boot
>> function which uses map_to_sysmem() to turn it into a address. Since the
>> pointer is not inside emulated DRAM, this will fail.
>>
>> Add a mapping feature which can handle any such pointer, mapping it to a
>> simple tag value which can be passed around in U-Boot as an address.
>>
>> Signed-off-by: Simon Glass <sjg at chromium.org>
>
> I think you are aware that this logic will fall apart spectacularly if
> any arithmetic operation happens on the virtual (U-Boot) address, right?
> So simple code like
>
>   readl(vaddr + 1);
>
> will just fail (hopefully) or (more likely) return a completely
> incorrect value.
>
> I assume this is intentional, but shouldn't the tag increment be
> something slightly larger then?

What do you expect readl() to do on sandbox? At present it is just a
no-op. I suppose we could support memory-mapped I/O but it has not
been attempted yet.

Regards,
Simon