• Mikael Pettersson's avatar
    pata_pdc2027x: PLL detection fixes · 78c4af0b
    Mikael Pettersson authored
    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: default avatarMikael Pettersson <mikpe@it.uu.se>
    Signed-off-by: default avatarJeff Garzik <jeff@garzik.org>
    78c4af0b
pata_pdc2027x.c 23.3 KB