On Tue, Sep 08, 2015 at 03:42:40PM +0200, Arnd Bergmann wrote: > On Thursday 03 September 2015 03:44:15 Luis R. Rodriguez wrote: > > On Sun, Aug 30, 2015 at 09:30:26PM +0200, Arnd Bergmann wrote: > > > On Friday 28 August 2015 17:17:27 Luis R. Rodriguez wrote: > > > > While at it, as with the ioremap*() variants, since we have no clear > > > > semantics yet well defined provide a solution for them that returns > > > > NULL. This allows architectures to move forward by defining pci_ioremap*() > > > > variants without requiring immediate changes to all architectures. Each > > > > architecture then can implement their own solution as needed and > > > > when they get to it. > > > > > > Which architectures are you thinking about here? > > > > Really only S390 would benefit from this now. > > Ok > > > > > Build tested with allyesconfig on: > > > > > > > > * S390 > > > > * x86_64 > > > > > > > > Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx> > > > > > > It's not really clear to me what the purpose of the patch is, is this > > > meant as a cleanup, or are you trying to avoid some real-life bugs > > > you ran into? > > > > Upon adding a new helper into CONFIG_PCI_IOMAP it was only through > > 0-day build testing that I found that I needed to add something for S390. > > This means we fix S390 reactively. With the asm-generic stuff in place > > to return NULL we don't need to do anything but a respective return > > NULL static inline, the moment that is done the author would know some > > architectures may not get support for the functionality they are adding. > > Without this we only find out reactively. > > Hmm, my gut feeling tells me that your approach won't solve the problem > in general. s390 PCI is just weird in many ways and it will occasionally > suffer from problems like this (as do other aspects of the s390 architecture > that are unlike the rest of the world). > > Maybe Martin and Heiko can comment on this, they may have a preference > from the s390 point of view. Hrm, so S390 is quirky is really odd ways that no other architecture is or is at least for now not expected to be ? > > > The version from lib/iomap.c seems correct for uses of CONFIG_GENERIC_IOMAP, > > > but most architectures can do better without that option. > > > > By do better do you mean a more optimized solution ? > > Yes: most architectures access the PCI I/O space through memory mapped I/O, > so we can return a regular __iomem pointer from ioport_map, rather than > a garbled pointer that the x86 version has to use. > > This means we also get to define iowrite32() to be identical to writel() > and can save the conditional for each caller. > > The lib/iomap.c version is really only needed for architectures that use > pointer access for PCI memory space, and special instructions for PCI > I/O space, like x86. s390 has special instructions for both, some > architectures do not have any I/O port access at all, and most of them > treat memory and I/O space the same way. I see, thanks. Luis -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
