I received the netbook from John last Saturday. It took a while to get
it integrated into my network as this is my first Fedora system, but I
now have some results to report.
I loaded wl logging both MMIO and PCI configuration register reads and
writes. The two types are now interleaved. The latter are logged with
trace_printk() calls. Note: There is a bug in current kernel code that
keeps these calls from being logged. Thanks to Stephen Rostedt for
sorting out this problem.
Both systems have the same core sequence and the same revisions. The
cores in order are ChipCommon rev 0x16, IEEE 802.11 rev 0x0F, PCMCIA rev
0x0A, and PCI-E rev 0x09.
I now know for certain that the netbook has an SPROM at offset 0x800.
Trying to read at offset 0x1000, which is the SPROM location in the
laptop, locks the machine, thus we need to determine the SPROM location
without reading 0x1000.
Fortunately, the wl driver reads and writes PCI configuration space from
the Linux shim code, not from the binary blob, thus these operations can
be traced.
The _only_ differences between the laptop and netbook operations between
startup and the reading of the SPROM are as follows:
Register Laptop Netbook Explanation
PCI 0x0C 0x10 0x08 Cache Line Size
PCI 0x04 0x00100106 0x001000006 Command Features [1]
Core 0 0x2C 0x10 0x12 Chip Status Reg [2]
Core 3 0x800 0x2801 0x3801 On laptop 0x3801 written
Core 3 0x280a 0x6dbe 0xedbe On laptop 0xedbe written
The code then switches to Core 1 (802.11) and begins reading SPROM. On
the laptop, it reads from 0x1000 and does a try at the smaller size
SPROM, then switches to the larger size, just as ssb does. On the
netbook, it immediately reads the larger size at offset 0x800.
I have not yet looked closely at the differences between wl and ssb, but
I did note one difference. In wl, bits 0xFF00 are cleared in PCI
register 0x40. The only thing I could find is this code fragment from
ipw2100 and ipw2200:
/* We disable the RETRY_TIMEOUT register (0x41) to keep
* PCI Tx retries from interfering with C3 CPU state */
pci_read_config_dword(pdev, 0x40, &val);
if ((val & 0x0000ff00) != 0)
pci_write_config_dword(pdev, 0x40, val & 0xffff00ff);
Larry
[1] The Wikipedia article on PCI configuration space says that this is a
bitmask of features that can be enabled/disabled. I have no explanation
of the details.
[2] This extra bit looks most promising of all the differences. It is
the bit involved in the is_sprom_available() routine for the 4315 device
in the Broadcom driver that has been reverse engineered; however, the
definition must have changed as that code would say there is no SPROM,
which is clearly untrue.
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