On Wed, Apr 15, 2015 at 4:59 PM, Andy Walls <awalls@xxxxxxxxxxxxxxxx> wrote: > On Wed, 2015-04-15 at 16:42 -0700, Andy Lutomirski wrote: >> On Wed, Apr 15, 2015 at 3:38 PM, Andy Walls <awalls@xxxxxxxxxxxxxxxx> wrote: > >> > >> >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
