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How so? Unless I'm missing something, this method, which is what I use, is not recursive and works just fine:Korona wrote:Recursive PCI enumeration does not hang PCs.
Recursive PCI enumeration is the only correct strategy to enumerate busses. For configuration mechanisms such as ECAM, non-recursive enumeration does not even work.
Code: Select all
let mut maxsg: u16 = 0;
(0..MAX_SG).for_each(|i| {
if regions.physical_address(i as u16, 0, 0, 0).is_some() {
maxsg += 1;
}
});
for sg in 0u16..maxsg {
for bus in 0..MAX_BUS {
for device in 0..MAX_DEVICE {
for function in 0..MAX_FUNCTION {
// Probe
}
}
}
}
How do you handle/detect nested/secondary/subordinate buses? Recursion seems to be the natural way to go about it.Ethin wrote: How so? Unless I'm missing something, this method, which is what I use, is not recursive and works just fine:
I don't treat a bridge or bus any differently than any other device. If I can scan it (that is, if the vendor ID isn't 0xFFFF or 0x0000), I add it. For bridges and such, I have this extra bit of handlign code:kzinti wrote:How do you handle/detect nested/secondary/subordinate buses? Recursion seems to be the natural way to go about it.Ethin wrote: How so? Unless I'm missing something, this method, which is what I use, is not recursive and works just fine:
Code: Select all
// Bridge or PCI card bus
secondary_bus: if (read_byte(addr as usize, HEADER_TYPE) & 0x7F)
== 1
|| (read_byte(addr as usize, HEADER_TYPE) & 0x7F) == 2
{
read_byte(addr as usize, SEC_BUS)
} else {
0
},
Okay, that works but that's kind of a hack -- using recursive enumeration you know a priori whether a bus number is valid or not.Ethin wrote:I use a method to check to see if the region I'm accessing in PCIe is actually a region in PCIe space but other than that, this is the code I'm using. Are you saying that this way isn't the right way?
Hmm... That definitely seems like a problem. I might switch my code to using the recursive initialization sequence then.Korona wrote:Okay, that works but that's kind of a hack -- using recursive enumeration you know a priori whether a bus number is valid or not.Ethin wrote:I use a method to check to see if the region I'm accessing in PCIe is actually a region in PCIe space but other than that, this is the code I'm using. Are you saying that this way isn't the right way?
Aside from that, there are situations where non-recursive enumeration truly does not work: for example, on most (all?) ARM devices, the firmware does not allocate bus numbers for you and you have to do it yourself once you see a bridge. The same is true even for x86 if you have a bridge on an expansion card.
That method is not recursive, but it will scan a lot of busses that are not actually present. And a lot of functions that are not present. I mean, the code will work, it's just doing a lot of useless nonsense.Ethin wrote:How so? Unless I'm missing something, this method, which is what I use, is not recursive and works just fine:
I would handle that by putting a separate PCI bridge initialization step before the actual enumeration. Besides, if I have to initialize PCI bridges, I will likely also have to initialize PCI BARs, and that is where it gets complicated without knowledge of the system.Korona wrote:Aside from that, there are situations where non-recursive enumeration truly does not work: for example, on most (all?) ARM devices, the firmware does not allocate bus numbers for you and you have to do it yourself once you see a bridge. The same is true even for x86 if you have a bridge on an expansion card.
To see all bridges, you have to see all devices anyway, so you can integrate these two kinds of iterations into a single recursive scan.nullplan wrote:I would handle that by putting a separate PCI bridge initialization step before the actual enumeration. Besides, if I have to initialize PCI bridges, I will likely also have to initialize PCI BARs, and that is where it gets complicated without knowledge of the system.