Hi Jon,

Jonathan Corbet schrieb:

On Fri, 09 Apr 2010 05:07:34 +0200
Florian Tobias Schandinat [off-list ref] wrote:

quoted

in your later patch "[PATCH 06/16] viafb: complete support for 
VX800/VX855 accelerated framebuffer" you reintroduce initializing those 
bits to 0. That's fine but I can't see a reason for preserving this bits 
here as it adds useless overhead unless the hardware itself changed some 
of those bits and behaves differently according to those bits. 

Somehow the cost of an additional MMIO read at mode setting time is
just not going to keep me up at night.

Well it's not only mode setting its for each hardware accelerated 
operation, but...

I will admit that I've learned to be rather superstitious when it comes
to messing with reserved bits.  Hardware designers like to hide
functionality like "bring down the wrath of the gods" behind such
bits.  The old code preserved them and worked, so I did the same.  I
don't see any real reason not to keep it.

...if you insist on it its okay with me. I still disagree but its 
nothing I can't live with.

quoted

Additionally the first 2 bits are not reserved but provide a rotation 
where 00 is what we want (no rotation).

That much is true, yes.  My mistake, will fix.

quoted

And if you rip code off hw_bitblt_2 it would be better to do the same 
with hw_bitblt_1. A quick look reveals that the same function can be 
used there (the error message would need to be adjusted but that's minor).

That had crossed my mind; there is quite a bit of duplicated code
between those two very long functions.  At the time I was focused on
making things work, and I didn't want to mess with code that I couldn't
actually test.  So further cleanup is on my list, but I would prefer to
defer it for a little bit.

The code (and the spec regarding the reserved bits also) is obviously 
identical so please don't ignore it. If you decide to put it in a 
separate function please do so for both blit engines especially if they 
really do the same as in this case. As you say they are mostly identical 
and that's by design. Please keep them in sync if possible. They exist 
that way to be a stateless and to avoid cluttering if's around.
(no need to say that I'll test those patches on my CLE266 and VX800 as 
soon as they apply cleanly to mainline)


Thanks,

Florian Tobias Schandinat