How disable attachment of sio(4) driver to device?

[John Baldwin]

On Saturday 22 October 2005 12:32 pm, M. Warner Losh wrote:
> In message: <200510221516.j9MFGnqT026691 at pinky.frank-behrens.de>
>
>             "Frank Behrens" <frank at pinky.sax.de> writes:
> : > Another solution would be to have your driver use the tty layer
> : > instead of banging the hardware directly, if that is compatible with
> : > the goals of your driver.  This solution isn't in quotes because for
> : > some class of devices (say a keyboard driver for a sun or apple newton
> : > keyboard that does serial), it might be the right one.
> :
> : Hm, this looks even more complicated and has more overhead. To show
> : shortly my requirements: The protocol is for an eib driver, (further
> : information on http://www.sax.de/~frank/eib4bsd/), it uses 9600 baud
> : on serial line. If the PC wants to send a telegram it resets RTS and
> : has to poll CTS. If CTS is active the transmission of one byte is
> : possible. If the last bit is sent (transceiver shift empty!) the PC
> : sets RTS and waits until CTS is inactive. Then a new handshake can
> : start and a transmission of about 30 bytes must be finished in 130
> : ms. IMHO this can be handled only in an interrupt routine with low
> : overhead.
>
> That's only about a 25% duty cycle on the line.  You might look at the
> uart driver to see if you can hook into it in such a way as to get the
> notification of these events via interrupt.  I thought that when the
> control bits changed there was an interrupt.
>
> : M. Warner Losh <imp at bsdimp.com> wrote on 21 Oct 2005 11:37:
> : > I'd like to be able to say that sio0 is at handle=\_SB_.PCI0.PX40.UAR2
> : > rather than some arbitrary address.  Or that bge1 is at
> : >
> : >             bge0 pnpinfo vendor=0x14e4 device=0x16a6 subvendor=0x14e4
> : > subdevice=0x8009 class=0x020000 at slot=3 function=0
> : > handle=\_SB_.PCI0.G0PA.LAN0 miibus0
> : >                 brgphy0 pnpinfo oui=0x818 model=0x16 rev=0x2 at phyno=1
> : >             bge1 pnpinfo vendor=0x14e4 device=0x16a6 subvendor=0x14e4
> : > subdevice=0x8009 class=0x020000 at slot=4 function=0
> : > handle=\_SB_.PCI0.G0PA.LAN1
> : >
> : > either at pci2.4.0 *OR* at handle=\_SB_.PCI0.G0PA.LAN1 (or even
> : > handle=LAN1).  So there'd need to be some kind of bus specific mapping
> : > function that would say true or false if a given device_t on that bus
> : > matched the string presented.
> :
> : For my driver I made already a sort of this. Part of my probe routine
> : is
> : 	if (resource_string_value(EIBNAME, 0, "at", &hintBus))
> : 		return (ENXIO);
> : 	if (strcmp(hintBus, "pci"))
> : 		return (ENXIO);
> :
> : 	if (resource_int_value(EIBNAME, 0, "bus", &hint) == 0 &&
> : 		pci_get_bus(device) != hint) {
> : 		return (ENXIO);
> : 	}
> : 	if (resource_int_value(EIBNAME, 0, "slot", &hint) == 0 &&
> : 		pci_get_slot(device) != hint) {
> : 		return (ENXIO);
> : 		}
> : 	if (resource_int_value(EIBNAME, 0, "function", &hint) == 0 &&
> : 		pci_get_function(device) != hint) {
> : 		return (ENXIO);
> : 	}
>
> There's problems doing this in the general case.  I tried doing
> something similar to this a few years back, and discovered that doing
> it in the driver caused problems.  Specifically, if another device is
> before you in the probe order, that device might snag the hinted
> device's location.  With most drivers returning BUS_PROBE_DEFAULT
> these days, this is effectively masked.  It is also tedious and
> error-prone to specificy things this way...  it will likely be
> completely adequate for most of your needs, however...
>
> : So my conclusion is:
> : 2. I will create a PR to change the sio(4) driver, that it returns
> : BUS_PROBE_DEFAULT instead of BUS_PROBE_SPECIFIC.
> : Then further patching is not necessary.
>
> I believe that's correct.

Only if you make sure that sio(4) doesn't try to pass data between probe() and 
attach() via the softc since the softc is preserved from probe to attach if 
you return 0 from probe.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org