[PATCH video-siliconmotion] Added detection of SM501 on PPC LocalBus.

[Francisco Jerez]

Marc Scherer <marc.scherer at mp-ndt.de> writes:

> This is the first patch in a series to make the Siliconmotion driver
> work with the TQM5200 Board.
>
> If no PCI device is found the driver tries to MMIO to the relevant
> location for a SM501 on PowerPC Localbus. If it finds the right device
> ID after MMIO-mapping it assumes the chip is there. If not it exits with
> an error message.
>
MMIO'ing arbitrary addresses is likely to make the X server crash when
there're no devices decoding it, do you have a more reliable way to
identify the TQM5200 board? Maybe '/proc/cpuinfo'?

> On my TQM5200, gcc reverses the bit-fields (which are heavily used).
> Therefore, the bit-accesses to the registers are all wrong. I have not
> found a way to reverse the bit-fields back to the right order.
>
> As an example, I have converted the bit-field access to the STATUS
> register to bit-masking. But all other bit-fields still have to be
> converted that way, too.
>
Yeah, that sounds reasonable to me, IMHO making the sm501 code access
the hardware via bitfields was an unfortunate choice because C makes no
internal representation guarantees.

> Anyway, with this patch, the driver should work as normal with the PCI
> devices. I cannot check this, could somebody please confirm?
>
> Regards,
> Marc
>
PS: Regarding the XAA vs EXA performance regression, have you tried to
benchmark EXA with 'Option "MigrationHeuristic" "greedy"'? It shouldn't
be that hard to make EXA play better with boards like this one, with
very limited composite capabilities. If you stick to XAA you aren't
going to get accelerated framebuffer rotations because they're
implemented using composite, not sure it's one of the use cases you're
interested in.

>
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