As I wrote a few weeks back, I am working on the extension to rtwn(4) to add
RTL8188EE support. At the moment, I am working on the Rx code, which handles
interrupts. After the interrupt is triggered, the code goes into the Rx routine
and delivers "junk data" in a continuous loop. It seems that the interrupt code
is **constantly** called - enough that the load average is frequently above 1.0.

I suspect the issue is giving the WiFi driver an acknowledgement of some sort,
but I am not certain. I attempted to copy Linux's interrupt code as best as
possible, but cannot determine if the error is within my code.

Here is a verbose explanation of what I believe Linux is doing and what I am
doing on FreeBSD.

-----Linux code works as follows-----

1. The IRQ trigger calls the function _rtl_pci_interrupt
2. This calls disable_interrupt, which for rtl8188ee is
   rtl88ee_disable_interrupt. This function writes IMR_DISABLED (0x0) to
   REG_HIMR (0xb0) and REG_HIMRE (0xb8).
3. Next _rtl_pci_interrupt calls interrupt_recognized(), a function pointer to
   rtl88ee_interrupt_recognized(), which:
   * Reads from REG_HISR (0xb4), stores the value in 'inta', ANDs that value by
     0x200084ff, then writes that value back to the same register.
   * Reads from REG_HISRE (0xbc), stores the value in 'intb', ANDs that value by
     0x100, then writes that value back to the same register.
   Then the function returns returns.

4. Back in _rtl_pci_interrupt if 'inta' is 0 and 'intb' is 0xffff, the code will
   skip step 5, goto to "done" and execute enable_interrupt code

5. If bit(0) is set to 1, this is an Rx interrupt and will run
   _rtl_pci_rx_interrupt(). From my review of the code, from here the Linux
   driver will read from the DMA memory and send the frame to the ieee80211
   layer. I only found 1 additional read instruction related to the power value,
   but nothing else is changed.

6. Here is the "done" portion, that happens no matter what, but is jumped to
   immediately as referenced above. It will call enable_interrupt(), a function
   pointer to rtl88ee_enable_Interrupt(), which will:
   a. Write 0x200084ff to REG_HIMR (0xb0)
   b. Write 0x100 to REG_HIMRE (0xb8)
   c. Write 0 to to REG_C2HEVT_CLEAR (0x01AF, A register having to do with C2H
   d. Write 0xc0 to REG_HSIMR (0x58 , I know this value from printf'ing it)

This is what I identified from reviewing from the Linux code.

-----My FreeBSD Code-----

My code is located here:

1. The IRQ trigger calls the function rtwn_pci_intr()
2. The equivalent of Linux's line 2 and 3 is in rtwn_classify_intr, which is a
   pointer to r88ee_enable_intr located in sys/dev/rtwn/rtl8188e/pci/r88ee_rx.
   This write's 0x0 to REG_HIMR (0xb0) and REG_HIMRE (0xb8)
3. Continuing, the same function:
   * Reads from ISR_MINE (same as REG_HISR, 0xb4), ANDs the value by 0x200084ff,
     store it in 'status'. Then I write the value back to the same register.
   * Read from REG_HISRE (0xbc), AND the value by 0x100, store it in 'statusb'.
     Write this value back to the same register.
   * Since this is an Rx register, the 'ret' value is AND'd by RTWN_PCI_INTR_RX.

4. In the Linux code, if 'status' is 0x0 and 'statusb' is 0xFFFF, it will goto
   to "done". On FreeBSD, it simply does not set any bits on the 'ret' value and
   the function returns 0, going back to rtwn_pci_intr.

5. Returning to rtwn_pci_intr(), if the 'ret' (now 'status') has
   RTWN_PCI_INTR_RX flag on, it executes rtwn_pci_tx_done(), which will read the
   DMA memory and send the frame to the ieee80211 layer. The execution will skip
   step 5 if 'ret' was 0 (the RTWN_PCI_INTR_RX flag was never set). This returns
   execution back to rtwn_pci_intr().

6. rtwn_pci_intr() concludes by running rtwn_pci_enable_intr(). This is similar
   to Linux's enable_interrupt(), it does the following:
   a. Write 0x200084f to R88EE_HIMR (0xb0)
   b. Write 0x100 to R88EE_HIMRE (0xb8)
   c. Write 0x0 to REG_C2HEVT_CLEAR (0x01AF)
   d. Write 0xc0 to REG_HSIMR


To me, it appears that I did a complete 1-to-1 copy of the Linux code. However,
in my case the driver is receiving constant interrupts without stopping. I am
not certain what I am missing or what is different. Could it be that something
outside of this particular code path was not properly set. If so, what might
that be?

Please advise.
Thank you,

Farhan Khan
PGP Fingerprint: B28D 2726 E2BC A97E 3854 5ABE 9A9F 00BC D525 16EE
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