On Wed, Apr 15, 2015 at 4:59 PM, Andy Walls [off-list ref] wrote:

On Wed, 2015-04-15 at 16:42 -0700, Andy Lutomirski wrote:

quoted

On Wed, Apr 15, 2015 at 3:38 PM, Andy Walls [off-list ref] wrote:

quoted

quoted

IMO the right solution would be to avoid ioremapping the whole bar at
startup.  Instead ioremap pieces once the driver learns what they are.
This wouldn't have any of these problems -- you'd ioremap() register
regions and you'd ioremap_wc() the framebuffer once you find it.  If
there are regions of unknown purpose, just don't map them all.

Would this be feasible?

Feasible? Maybe.

Worth the time and effort for end-of-life, convential PCI hardware so I
can have an optimally performing X display on a Standard Def Analog TV
screen?   Nope. I don't have that level of nostalgia.

The point is actually to let us unexport or delete mtrr_add.  We can
either severely regress performance on ivtv on PAT-capable hardware if
we naively switch it to arch_phys_wc_add or we can do something else.
The something else remains to be determined.

We sort of know where some things are in the MMIO space due to
experimentation and past efforts examining the firmware binary.

Documentation/video4linux/cx2341x/fw-*.txt documents some things.  The
driver code actually codifies a little bit more knowledge.

The driver code for doing transfers between host and card is complex and
fragile with some streams that use DMA, other streams that use PIO,
digging VBI data straight out of card memory, and scatter-gather being
broken on newer firmwares.  Playing around with ioremapping will be hard
to get right and likely cause something in the code to break for the
primary use case of the ivtv supported cards.

Ick.

If the only thing that really wants WC is the esoteric framebuffer
thing, could we just switch to arch_phys_wc_add and assume that no one
will care about the regression on new CPUs with ivtv cards?


--Andy