Re: [Qemu-arm] [PATCH 4/7] m25p80: add a m25p80_set_rom_storage() routine

[Cédric Le Goater]

On 07/04/2016 08:12 PM, Cédric Le Goater wrote:
> On 07/04/2016 07:57 PM, mar.krzeminski wrote:
>>
>>
>> W dniu 04.07.2016 o 14:18, Cédric Le Goater pisze:
>>> Some SPI controllers, such as the Aspeed AST2400, have a mode in which
>>> accesses to the flash content are no different than doing MMIOs. The
>>> controller generates all the necessary commands to load (or store)
>>> data in memory.
>>>
>>> To emulate such a behavior, we need to have access to the underlying
>>> storage of the flash object. The purpose of the routine is to set the
>>> storage of a preinitialized SPI flash object, which can then be used
>>> by the object itself but also by a SPI controller to handled the
>>> MMIOs.
>> Hi,
>>
>> I am not sure if this approach is correct. I can not find any datasheet
>> to this SPI controller, but as you mentioned in first paragraph, controller
>> generates all commands (probably ones are somehow configurable).
> 
> yes. see this patch :
> 
>       http://lists.nongnu.org/archive/html/qemu-devel/2016-06/msg08229.html
> 
>       /* CEx Control Register */
>       #define R_CTRL0           (0x10 / 4)
>       #define   CTRL_CMD_SHIFT           16
>       #define   CTRL_CMD_MASK            0xff
> 
> 
>> In this series you hack this behaviour and you do direct access to file.
> 
> It is true it is not very respectful of the m25p80 interface.
> 
>> IMHO you should emulate sending such commands in SPI controller
>> model.
> 
> I will give it a try. I don't think the alternative is a complex 
> change anyhow.

So yes, that would work out pretty well. But there is another need 
that does not show up in the series (I am not splitting the patches 
correctly I guess) We would like to boot directly from a flash image. 
For this purpose, the pflash_cfi object uses a memory region of type 
rom and uses the storage behind the region.

m25p80_set_rom_storage() is probably not the right API to share the 
storage. I am looking for a way to handle this without changing too
much m25p80, which does not have a mem region currently. Suggestions 
welcomed ! :) 

Thanks,

C.