On Tue, May 03, 2022 at 01:08:04PM +0000, David Laight wrote: > From: Linus Walleij > > Sent: 01 May 2022 22:56 > > > > On Fri, Apr 29, 2022 at 5:37 PM William Breathitt Gray > > <william.gray@xxxxxxxxxx> wrote: > > > On Fri, Apr 29, 2022 at 04:46:00PM +0200, Niklas Schnelle wrote: > > > > > > Good question. As far as I can see most (all?) of these have "select > > > > ISA_BUS_API" which is "def_bool ISA". Now "config ISA" seems to > > > > currently be repeated in architectures and doesn't have an explicit > > > > HAS_IOPORT dependency (it maybe should have one). But it does only make > > > > sense on architectures with HAS_IOPORT set. > > > > > > There is such a thing as ISA DMA, but you'll still need to initialize > > > the device via the IO Port bus first, so perhaps setting HAS_IOPORT for > > > "config ISA" is the right thing to do: all ISA devices are expected to > > > communicate in some way via ioport. > > > > Adding that dependency seems like the right solution to me. > > I think it all depends on what HAS_IOPORT is meant to mean and > how portable kernel binaries need to be. > > x86 is (probably) the only architecture that actually has 'in' > and 'out' instructions - but that doesn't mean that some other > cpu (and I mean cpu+pcb not architecture) have the ability to > generate 'IO' bus cycles on a specific physical bus. > > While the obvious case is a physical address window that generates > PCI(e) IO cycles from normal memory cycles it isn't the only one. > > I've used sparc cpu systems that have pcmcia card slots. > These are pretty much ISA and the drivers might expect to > access port 0x300 (etc) - certainly that would be right on x86. > > In this case is isn't so much that the ISA_BUS depends on support > for in/out but that presence of the ISA bus provides the required > in/out support. That's true, it does seem somewhat backwards to have a depends on line when the bus is really just providing the support for devices that want to use it rather than requiring it. Do you think a HAVE_IOPORT line should be added independently for each driver instead of adding it to ISA_BUS? > Now, maybe, the drivers should be using some ioremap variant and > then calling ioread8() rather than directly calling inb(). > But that seems orthogonal to this changeset. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) Using ioremap() does have the benefit of making it easier to reuse the code for some of these PC104 drivers with their PCI device variants; the ioread8() calls and such can stay the same and we just initialize to the proper address during probe. I plan to look into this in the future then. William Breathitt Gray
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