Messages in this thread | | | Date | Thu, 03 Apr 2008 17:54:51 +0200 | From | Rene Herman <> | Subject | Re: [patch 00/37] PNP resource_table cleanups, v2 |
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On 02-04-08 23:35, Bjorn Helgaas wrote:
>> By the way, the original isapnp_parse_id explicitly encodes the top _6_ >> bits in str[0] (& 0x3f) which seems odd. Bit 31 had better be 0 indeed, >> but I wonder why the original didn't just assume such. > > Yes, I wonder about that, too. Including that bit would mean that > the first character of PNP IDs could include characters at offsets > 0x20-0x3f, i.e., "`a..z{|}~" and DEL. I poked around and found > some IDs that seem to depend on that, e.g., "nEC8241" in the 8250_pnp > serial driver.
Oh well, PC hardware...
> I changed this to include six bits for the first character, and > masked off the top bit in PNPBIOS. I think that should preserve > the previous behavior; see what you think.
Yes, it should. I checked the ISAPnP specification and it explicitly fixes bit 31 at 0 (and defines the "compressed ASCII" as 5 bits). Given what you describe you probably don't have a good place to stash a comment but with 6 bits being non-spec something like "appease broken ISAPnP hardware" would probably be good.
>> 2: There are 4 tests for ACPI_READ_WRITE_MEMORY here which are turned >> into IORESOURCE_MEM_WRITEABLE or 0. Not sure, but should they be >> turned into IORESOURCE_MEM_WRITEABLE or IORESOURCE_READONLY? > > One would expect that "mem.write_protect == 1" would mean read-only. > Unfortunately, I'm too lazy to un-obfuscate the ACPI CA logic that > deals with mem.write_protect, since it seems to be all table-driven. > In the absence of understanding, I tried to preserve the existing > behavior. I think I did, i.e., if "write_protect == ACPI_READ_WRITE_MEMORY", > we add in IORESOURCE_MEM_WRITEABLE, otherwise do nothing. If I > goofed that up, let me know.
No, you didn't, is fine.
> I have an ISA question here, too: previously isapnp_read_resources() > set only res.start for IO and MMIO resources and left res.end unset > (should be zero, I think). I don't think ISA tells you the size, so > I assumed "1", but I don't know if that's the right thing to do. My > reasoning was "zero is obviously wrong, two could be too big and > generate bogus conflicts, so one is the only possible choice."
Yes, as far as I'm aware the actual value is of no consequence. The size is not a setable parameter; to hardware they're only base address registers, It used to be kept simply at -1 (in an unsigned sort of way) and as far as I'm aware, we're also not interested yet at this level.
However, now that you made me look closer and in context -- there's actually a possibly somewhat serious problem here.
isapnp_read_resources() stores the resources as read from the hardware at the index in the table that matches the actual index in the hardware and isapnp_set_resources() stores them back into those same hardware indices.
Now by using pnp_add_foo_resource() which just scans for the first _UNSET resource, the resources might not end up in the same linear position in table/list if intermediate resources were unset in hardware (!ret). A subsequent isapnp_set_resources() would them restore the value to the wrong hardware index.
The IORESOURCE_ flags currently reserve too few bits (IORESOURCE_BITS, 8) to be able to store the hardware index: IORESOURCE_MEM and IORESOURCE_DMA need 2 and 1 respectively and there are 1 and 0 available respectively. It's ofcourse possible to hijack a few more bits in IORESOURCE_ flags but you're turning this into a list. I suppose the idea is to make it a simple list of struct resource, but perhaps a resource-private "driver_data" sort of field comes in handy for more than this already? Swiping more of IORESOURCE_ is a bit ugly...
In any case, I missed this, but ISAPnP is still (at least in principle) broken with the current set therefore.
> I also made the _len() functions inlines and restructured the logic in > both _len() and _valid() functions. I couldn't stand the thought of all > those extra list traversals in there :-) I'd appreciate a double-check > of that.
Will do.
Rene.
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