Setting IDE Bus speed during boot

[j.natowitz-KealBaEQdz4 at public.gmane.org (Jerry Natowitz)]

Actually the idebus parameter doesn't change the PCI bus speed, it set 
the bus speed in the calculations for how many bus cycles to wait for 
various operations in Programmed I/O (PIO).  If you change a bus clock 
that your chipset uses to set the PCI bus clock, you should set idebus.

For instance, if you change the system clock from 200 MHz to 220, you 
should divide 220 by 6 (200/33 ~= 6) and round up, using idebus=37.

	Jerry Natowitz
	j.natowitz (at) rcn.com
	Owner of Unix port 1572 (chip-lm), as found by Google
	and returned to the IANA 2009/12/15


Dan Ritter wrote:
> On Wed, Jan 13, 2010 at 12:12:41PM -0500, bill-CIZd1d4GmLheoWH0uzbU5w at public.gmane.org wrote:
>> Thanks for reading this. 
>>
>> I have a Debian system, and during bootup today, I noticed these 
>> entries in the syslog (some lines snipped):
>>
>> kernel: ..... CPU clock speed is 601.0226 MHz.
>> kernel: ..... host bus clock speed is 66.0802 MHz.
>>
>> kernel: ide: Assuming 33MHz system bus speed for PIO modes; \
>>      override with idebus=xx
>>
>> So, I changed the boot line as follows:
>>
>> kernel: Kernel command line: root=/dev/hda1 ro idebus=66
>>
>> But, I got these results:
>>
>> kernel: ide: Assuming 66MHz system bus speed for PIO modes
>> kernel: vesafb: probe of vesafb0 failed with error -6
>> kernel: NET: Registered protocol family 1
>> kernel: VP_IDE: IDE controller at PCI slot 0000:00:07.1
>> kernel: VP_IDE: chipset revision 16
>> kernel: VP_IDE: not 100%% native mode: will probe irqs later
>> kernel: VP_IDE: User given PCI clock speed impossible (66000), using 33 MHz instead.
>>
>> ... and I'd like all devices to use the bus at 66MHz, so please tell me how. Thank you.
> 
> That's the clockspeed of the bus that the IDE adapter is
> attached to -- in this case, PCI. You don't want to try to
> change that, really.
> 
> (yes, it's badly named.)
> 
> Instead, use hdparm to work on each individual ide device.
> 
> -dsr-
> 
>