Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision
Previous revision
soc:2009:oremanj:journal:week12 [2009/08/11 22:54]
rwcr
soc:2009:oremanj:journal:week12 [2009/08/15 01:36] (current)
rwcr
Line 4: Line 4:
  
 Also, I believe this IRC message needs to find a permanent record here: Also, I believe this IRC message needs to find a permanent record here:
-  10:45 <     ​mcb30> At the point you're talking about, the system is not fully initialised. ​ On many systems, the memory map +  10:45 <​mcb30>​ At the point you're talking about, the system is not  
-                     ​is not yet valid. ​ If running normal BIOS-level code is marked with "Here be dragons",​ running during POST +                ​fully initialised. ​ On many systems, the memory map 
-                     ​is marked with "Here be huge, ugly, vindictive, sociopathic dragons with a mean sense of humour"​+                is not yet valid. ​ If running normal BIOS-level code 
 +                ​is marked with "Here be dragons",​ running during POST 
 +                is marked with "Here be huge, ugly, vindictive, sociopathic 
 +                ​dragons with a mean sense of humour"​
 Well put indeed! Well put indeed!
  
Line 41: Line 44:
 Thought about future driver support; it seems that the combination of //b43//, //ath9k//, and //iwlwifi// should support almost all currently-unsupported cards in common use. Each of these drivers is over 20,000 lines of C in the Linux kernel, though, so this won't be an easy task. Thought about future driver support; it seems that the combination of //b43//, //ath9k//, and //iwlwifi// should support almost all currently-unsupported cards in common use. Each of these drivers is over 20,000 lines of C in the Linux kernel, though, so this won't be an easy task.
  
 +==== Wednesday, 12 August ====
 +Mostly worked on the ROM-from-PCI loader, which can be found as branch **xrom** in my personal repository for the curious. I doubt I'll be cleaning this up for mainline, as there seems to be no really safe way of doing it, and newer systems with PCI3.0 and PMM get the benefit for free.
 +
 +==== Thursday, 13 August ====
 +Wrote some [[:​wirelessboot:​implementation|implementation notes]] for the wireless code.
 +
 +Updated branch **linker** in staging to add the line number to symbols generated by ''​REQUIRE_SYMBOL(foo)'',​ so that they now look like e.g. ''​_''''​_require_foo_47''​. This fixes an issue with ''​REQUIRE_OBJECT()''​ multiple times in the same file (e.g. with both ''​GDBUDP''​ and ''​GDBSERIAL''​ defined); now that the symbols that macro introduces are initialized data rather than common, the compiler refuses to allow two with the same name.
 +
 +Discovered that a stock e1000 gPXE ROM does not work on my development system (very recent BIOS, PCI3.0/​BBS/​PMM). It seems the BIOS will refuse to hand out 1MB or more at a time using PMM, and since gPXE keeps requesting larger allocations until it gets one aligned to 2MB, gPXE doesn'​t use PMM at all. The ROM is 70656 bytes, and it's relocated 71680 bytes below the end of option ROM space. Loading gPXE from the POST-time prompt works fine (except that e820 is not yet available there on my system); loading it as a boot device freezes immediately after "gPXE starting execution...",​ and I get garbage onscreen after 10 seconds or so. I suspect some other card is trampling on our tail and hopelessly confusing the decompressor.
 +
 +It turns out my test system exhibits the same underlying problem (BIOS won't give out 1MB or more via PMM); it just has slightly more option ROM space. When I tried to test a fix that would accept A20-set allocations if the BIOS had set up the A20 line properly, I managed to brick my e1000 //again//. Forty minutes of shuffling around PCI cards later, I fixed things, and verified that the state of the A20 line during POST is no indication of the state of A20 when our BEV or int19h is called. The BIOS disables it before booting.
 +
 +Fix that would allow us to use PMM (and thus larger ROMs) on such limited BIOSes: accept any PMM buffer address, and set the A20 gate ourselves in the BEV. The code to do this is rather messy, though, and might not be worth it.
 +
 +Also discovered a small bug in ''​src/​arch/​i386/​firmware/​pcbios/​gateA20.c'':​
 +  #define A20_KBC_RETRIES ​        ​(2^21)
 +"You keep on using that operator. I do not think it means what you think it means."​ :-)
 +
 +==== Friday, 14 August ====
 +On my test system, if we make use of a PMM buffer with A20 set, we don't even get to the BEV entry point to have a chance to set the A20 gate up properly. Adding a
 +  ljmp    $0xf000, $0xfff0
 +immediately after ''​bev_entry:'',​ which reboots the system at that point on a PMMless gPXE, does not prevent the freeze. There may be a subtler issue here.
 +
 +Started taking a look at the Linux ''​b43''​ (Broadcom wireless) driver. It's quite well-written and -commented, especially for a reverse-engineered driver, but the hardware is really a mess. Some models have the 30-bit DMA restriction Stefan dealt with during his SoC last year. The hardware uses an SSB interface, which seems to be on the level of a whole different bus bridged to PCI. And then there'​s this line:
 +          err = request_firmware(&​blob,​ ctx->​fwname,​ ctx->​dev->​dev->​dev);​
 +''​dev->​dev->​dev''?​ Seriously? :-)
 +
 +Figured out a possible solution for the problem for **xrom** that we can't know about the devices like APICs that don't have their mappings in PCI BARs: just read the entire space we're going to cover with our mapping before we map it. The standard on x86 is for unmapped memory to read all-ones, and designers of MMIO interfaces actively avoid all-ones being normal in a register. If all 128k or whatever read as ''​0xFF'',​ plus we find no overlap in BARs or e820, it's almost certainly safe to map.
 +
 +The ROM-mapping logic could also be used for UNDI.
 +
 +Split up the FireWire branch into a more logical separation of commits (first the generic interface, then the gPXE code that uses it, then the host-side utilities to make it useful). Pushed it as **firewire** to my personal repository and removed it from staging, as I have other code there that I think is more important (specifically **linker** and the various things depending on it).
 +
 +==== Final Thoughts ====
 +
 +Well, Summer of Code is over, and what an adventure it's been. I've immensely enjoyed working on such a mature and well-developed codebase, with a great many talented people, and in a very interesting field with lots of room for innovation. Thank you to everyone who's helped to make it possible!
 +
 +Things I'd like to still get done, in rough order of priority:
 +  * Merge branch **linker** to mainline.
 +  * Merge branch **wireless** to mainline, with all the crypto and iwmgmt stuff.
 +  * Get branch **firmware** ready for mainline.
 +  * Get branch **firewire** ready for mainline, in one form or another. (It may be a very useful interface for driving gPXE for testing, a la DrV's project.)
 +  * Write **xrom** in a fashion that's remotely valid, doing the grunt work of scanning PCI BARs and e820 and such to look for a valid place to map instead of the ugly and immoral hack I initially went with.
 +  * In the Maybe category:
 +    * Extend branch **eap** into some real support for EAP / WPA Enterprise authentication,​ with a few common methods implemented.
 +    * Port driver ''​ath9k''​ or ''​b43''​ or ''​iwlwifi''​ from Linux. The latter two require firmware loading, and all are something of a mess.
 +    * Add standardized support for NV options using the VPD area or (on EFI) RuntimeServices->​SetVariable(). The storing in EEPROM using NVS is nice, but most cards don't support it because their EEPROM is earmarked for other purposes. With wireless cards especially, another spot is needed for SSID and encryption key.
 +
 +Final sanity check of local git branches related to the work I've done:
 +  ath5k                  Merged (ath5k wireless driver)
 +  bigrom-oremanj ​        ​Merged (small patch to support big ROMs)
 +  sky2                   ​Merged (sky2 wired NIC driver)
 +  mainline-review ​       Merged (initial bout of wireless code)
 +  wiprocfix ​             Merged (small patch to wireless code)
 +  linker ​                In staging (improve linker macros, object-specific config)
 +  firewire ​              ​Waiting (debugging interface over FireWire)
 +  firmware-pretty ​       Waiting (firmware image embedding and loading)
 +  wireless-pretty ​       Waiting (wireless crypto and improvements)
 +  eap                    To-do (802.1X authentication,​ WPA Enterprise)
 +  xrom                   To-do (load ROM from the PCI card)
 +  ath5k-old ​             History (superseded by ath5k)
 +  firewire-old ​          ​History (superseded by firewire)
 +  firewire-really-old ​   History (superseded by firewire)
 +  wireless ​              ​History (superseded by wireless-pretty)
 +  fwtrans ​               Academic interest (load files over firewire debug link)
 +
 +And so we go, again.
 +
 +Thank you to everyone who's made this summer great, and I hope to be able to continue contributing! :-)

QR Code
QR Code soc:2009:oremanj:journal:week12 (generated for current page)