re: defxx: DEFEA's ESIC port I/O decoding cleanup

Maciej W. Rozycki
2014-10-01T17:20:00Z

On Wed, 1 Oct 2014, Dan Carpenter wrote:

> The patch b98dfaf2b0a3: "defxx: DEFEA's ESIC port I/O decoding
> cleanup" from Sep 25, 2014, leads to the following static checker
> warning:
>
> drivers/net/fddi/defxx.c:741 dfx_bus_init()
> warn: odd binop '0x3 & 0xfffffffffffffffc'
>
> drivers/net/fddi/defxx.c
> 729 val = PI_IO_CMP_M_SLOT;
> 730 outb(val, base_addr + PI_ESIC_K_IO_ADD_MASK_0_1);
> 731 val = (PI_ESIC_K_CSR_IO_LEN - 1) & ~3;
> 732 outb(val, base_addr + PI_ESIC_K_IO_ADD_MASK_0_0);
> 733
> 734 val = 0;
> 735 outb(val, base_addr + PI_ESIC_K_IO_ADD_CMP_1_1);
> 736 val = PI_DEFEA_K_BURST_HOLDOFF;
> 737 outb(val, base_addr + PI_ESIC_K_IO_ADD_CMP_1_0);
> 738
> 739 val = PI_IO_CMP_M_SLOT;
> 740 outb(val, base_addr + PI_ESIC_K_IO_ADD_MASK_1_1);
> 741 val = (PI_ESIC_K_BURST_HOLDOFF_LEN - 1) & ~3;
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This is just saying "val = 0" in a complicated way. It's not clear what
> was intended...
>
> 742 outb(val, base_addr + PI_ESIC_K_IO_ADD_MASK_1_0);
> 743

This is self-documenting code, plus if PI_ESIC_K_BURST_HOLDOFF_LEN is
ever set to something else to what it is now (please be aware this piece
of hardware is not fully documented), then there'll be no need to review
code throughout to update mask calculation. See a similar calculation for
PI_ESIC_K_CSR_IO_LEN and the board's other address decode register above.

In this case the resulting mask comes out as all-zeros, meaning no
address bits will be discarded in decoding, i.e. only a single address
will match, which is exactly what is needed here. This is a 32-bit
register we don't want partial accesses to and hence the ~3 mask.

I think your checker might be just a little bit too picky for this case,
although I realise this pickiness may catch dumb mistakes elsewhere and
save people trouble where a pair of disjoint mask is not really intended
unlike here. Thanks for the heads-up therefore, but this code is good and
I plan to keep it like this. :)

Maciej