Re: [Qemu-devel] [PATCH V4 0/5] Ehnahced SSI bus support + M25P80 SPI flash + Xilinx SPI controller

[John Williams]

Hi Paul,

On Tue, Jun 5, 2012 at 11:34 AM, Paul Brook <address@hidden> wrote:
>> Patch 1 Enhances SSI bus support to properly support multiple attached
>> devices. An api is provided for SSI/SPI masters to select a particular
>> device attached to the bus.
>>
>> Patch 2 is a device model for the m25p80 style SPI flash chip.
>>
>> Patch 3 is  the Xilinx XPS SPI contoller. Its a sysbus device that
>> instantiates a ssi bus, and interfaces the two (as per the controllers
>> functionality)
>>
>> Patch 4 instantiates the XPS SPI controller in the petalogix ML605
>> reference platform and connects two m25p80s to it.
>>
>> Patch 5 updates the stellaris machine model to use the multi slave SSI
>> support
>
> I'm still not convinced modelling this as a multipoint bus is a good idea.  If
> nothing else you've failed to model the case where multiple slaves are
> selected simultanously.  Given the chip selects are actual wires, not part of
> the bus itself, I think multiple point-point busses are a better fit.
>

On 5th April, when we first RFC'd our SPI layer support, you said to Peter:

==
I don't believe there is any difference between SSI and SPI.  It's the exact
same thing - the same way that many devices support a "two-wire interface"
that is actually just I2C with a different name.

The behavior of the CS pin varies between devices.  It sounds like you need a
bit of extra logic not present in the current ssi code.  You should fix that,
not invent a whole new bus.
==

He's gone and done exactly that, indeed generalised it with the
proposed changes to SSI.

If you don't like how he's done the Stellaris change then feel free to
NACK that specific patch, but otherwise it seems this generic SSI set
should be good to go now?

Thanks,

John
--
John Williams, PhD, B. Eng, B. IT
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com  p: +61-7-30090663  f: +61-7-30090663