aboutsummaryrefslogtreecommitdiffstats
path: root/drivers/ata/pata_sis.c
diff options
context:
space:
mode:
authorMikael Pettersson <mikpe@it.uu.se>2007-08-18 16:58:53 -0400
committerJeff Garzik <jeff@garzik.org>2007-08-23 05:32:07 -0400
commit78c4af0b43e152c40d232137f8cb637f2c58826a (patch)
treeeac864762ba107d041a1760823881704317e3836 /drivers/ata/pata_sis.c
parent8270bec40075eec9df8778c1d5da36ef0e535176 (diff)
pata_pdc2027x: PLL detection fixes
Previously I reported that the pata_pdc2027x PLL detection changes in kernel 2.6.22 broke the driver on my PowerMac: >pata_pdc2027x: Invalid PLL input clock 1691742kHz, give up! This is followed by a number of errors and speed reduction steps on the affected ports. There are two bugs in pata_pdc2027x's PLL detection code: 1. The PLL counter's start value is read before the chip is put in "test mode". Outside of test mode the counter is halted, and on the PowerMac the counter is zero because the chip hasn't been initialised by its BIOS. The fix is to move the read of the start value to after test mode is started, but before the mdelay() in test mode. This also improves the precision of the PLL detection. 2. The code to compute the number of PLL decrements during the mdelay() in test mode fails to consider that the PLL counter only is 30 bits wide. If there is a wraparound, it will compute an incorrect and much too large value. On the PowerMac, the start count is zero, the end count is a large 30-bit value, so wraparound occurs and an out of bounds PLL clock is detected. The fix is to mask the (start - end) computation to 30 bits. While debugging this I also noticed that pdc_read_counter() reads the two halves of the 30-bit PLL counter as 16-bit values, and then combines them as if the halves only are 15 bits wide. To avoid confusion, the halves should be read as 15-bit values. This patch implements all three changes. It fixes the PLL detection failure on my PowerMac, and doesn't cause any regressions on an x86 with an identical card. Signed-off-by: Mikael Pettersson <mikpe@it.uu.se> Signed-off-by: Jeff Garzik <jeff@garzik.org>
Diffstat (limited to 'drivers/ata/pata_sis.c')
0 files changed, 0 insertions, 0 deletions