Re: [PATCH] IBM Lanstreamer bugfixes (round 3)

Jeff Garzik
2002-03-04T19:10:20Z

Kent Yoder wrote:
> Ok, hopefully below is the section you were referring to:
>
> -------
>
> pci_read_config_byte(pdev, PCI_CACHE_LINE_SIZE, &cls);
> cls <<= 2;
> if (cls != SMP_CACHE_BYTES) {
> printk(KERN_INFO " PCI cache line size set incorrectly "
> "(%i bytes) by BIOS/FW, ", cls);
> if (cls > SMP_CACHE_BYTES)
> printk("expecting %i\n", SMP_CACHE_BYTES);
> else {
> printk("correcting to %i\n", SMP_CACHE_BYTES);
> pci_write_config_byte(pdev, PCI_CACHE_LINE_SIZE,
> SMP_CACHE_BYTES >> 2);
> }
> }

this gets cache line size correct

> /* Turn off Fast B2B enable */
> pcr &= ~PCI_COMMAND_FAST_BACK;
> /* Turn on SERR# enable and others */
> pcr |= (PCI_COMMAND_SERR | PCI_COMMAND_INVALIDATE | PCI_COMMAND_PARITY |
> PCI_COMMAND_IO | PCI_COMMAND_MEMORY);
>
> pci_write_config_word (pdev, PCI_COMMAND, pcr);
> pci_read_config_word (pdev, PCI_COMMAND, &pcr);

You only need to worry about the PCI_COMMAND_INVALIDATE bit here, unless
your chip requires other setup, or you care to handle PCI hard errors in
the driver.

> Out of curiosity, does it in fact make sense to use memory write and
> invalidate and set cache line size to 0 in some cases? This seems to go
> against the PCI spec, which, if I'm reading it correctly, says that memory
> write and invalidate is the same as a memory write, but it guarantees that
> at least 1 cache line will be written. So, setting cacheline size =0 would
> negate this effect(?)

The rule is, never ever enable MWI if cache line size is zero.

MWI -does- make a difference in performance, though you may need to
check lanstreamer docs to see if there is a chip-specific MWI bit you
need to enable, over and above the PCI_COMMAND bit.

Jeff

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Jeff Garzik |
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