[PATCH 2/11] cell: generalize io-workarounds code

[Ishizaki Kou]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote:
> I may have missed something in your patch but if the workarounds are
> specific to a given bridge, they may as well set the top level
> indirections once straight to the right workarounds.
> 
> Also, my understanding is that we are pretty much using the same 
> bridge on the cell blades, so is there any way that can be
> consolidated rather than having function pointers ?

Celleb has two different bus bridges such as PCI and PCI-Express, and 
they have different bus access methods. Cell blades support only one 
PCI, so you may have only one indirect access method. That is why I 
introduced second level indirect function.
Considering to embed 'second level' indirect function into first level 
macros, it may break iSeries.

> I'll try to have a closer look next week, but I'm a bit worried by
> having all IO go through 2 level of function pointers, the PPE isn't
> very good at it and this will slow things down more than they already
> are.

Only on celleb, all IO go through 2 level of function pointers.
 
On cell blades, you can set global variable "ppc_pci_io" up at function 
spider_pci_workaround_init() directly instead of calling function
io_workaround_init(), so all IO on cell blades use only one level of 
function pointer which is stored in ppc_pci_io.


> > I may have missed something in your patch but if the workarounds are
> > specific to a given bridge, they may as well set the top level
> > indirections once straight to the right workarounds.
> 
> Looking more closely, I wonder if a good solution would be to move the
> function pointers away from globals, to the dev_archdata structure,
> and thus make them per-device (like the DMA ops)

As you said, if read/write/in/out functions take device parameter,
taking I/O function pointers into the dev_archdata structure should be
the best solution. But they don't take device parameter, and they must
search I/O function pointers with address parameter. I think it's
better they search pointers from bus bridges, because access mothod
for a device on its parent bus bridge, not device itself.

Best regards,
Kou Ishizaki