Dear Arnd Bergmann, On Wed, 30 Jan 2013 09:55:49 +0000, Arnd Bergmann wrote: > I don't remember the kernel ever caring about whether hardware complies > to a standard or not. The kernel's job is to make hardware work, based > on the actual implementation of that hardware. In a lot of cases that > means taking the standard document as a reference, and adding quirks > for the devices that are different. > > In the end, it comes down to the impact on the code complexity, and > the run-time overhead for whatever hardware is most common when adding > those quirks. This is not only about standards, it is also about re-using the PCI resource allocation code. In my RFCv1, sent December, 7th, I wasn't using any emulated PCI-to-PCI bridge. So it *can* perfectly work without it. However, one major drawback of my RFCv1 version is that since I didn't know how much I/O space and memory space was needed for each PCIe device, I had to oversize the address decoding windows. And also, I had to have a special allocator (certainly simple, but still) to find an available physical address to set up each address decoding window. Emulating a PCI-to-PCI bridge very nicely allows to re-use the PCI core resource allocation code. I think it's really the main reason for emulated those PCI-to-PCI bridges, rather than willing to comply to some standards. So what I'm going to do now is rework my patch series by removing the emulated host bridge (which is normally mandatory by PCIe standard, but Linux doesn't need it, so we don't care), but I'll keep the emulated PCI-to-PCI bridges in order to benefit for the PCI core resource allocation mechanisms. Is this ok for you? I'd like to settle on the strategy to follow, because we're really going a funny road here: on December 7th, I submit a series that doesn't use any PCI-to-PCI bridge, and I'm told that I should emulate some. I spent a long time working on an implementation that uses emumlated PCI-to-PCI bridges, which I submitted on Monday, now to be told that I should work really hard not to use PCI-to-PCI bridges. I hope you can feel my little embarrassment here... Thanks, Thomas -- Thomas Petazzoni, Free Electrons Kernel, drivers, real-time and embedded Linux development, consulting, training and support. http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
