Jeff Garzik wrote: > Mikael Pettersson wrote: > >> 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@xxxxxxxx> > > > Fantastic! Thanks for putting in a great effort to track these down. > > I'll queue it up [unless someone responds with a problem requiring > revision, of course] > > >> diff -rupN linux-2.6.23-rc3/drivers/ata/pata_pdc2027x.c >> linux-2.6.23-rc3.pata_pdc2027x-pll-detection-fixes/drivers/ata/pata_pdc2027x.c >> >> --- linux-2.6.23-rc3/drivers/ata/pata_pdc2027x.c 2007-07-09 >> 22:01:31.000000000 +0200 >> +++ >> linux-2.6.23-rc3.pata_pdc2027x-pll-detection-fixes/drivers/ata/pata_pdc2027x.c >> 2007-08-18 21:53:40.000000000 +0200 >> @@ -563,13 +563,13 @@ static long pdc_read_counter(struct ata_ >> u32 bccrl, bccrh, bccrlv, bccrhv; >> >> retry: >> - bccrl = readl(mmio_base + PDC_BYTE_COUNT) & 0xffff; >> - bccrh = readl(mmio_base + PDC_BYTE_COUNT + 0x100) & 0xffff; >> + bccrl = readl(mmio_base + PDC_BYTE_COUNT) & 0x7fff; >> + bccrh = readl(mmio_base + PDC_BYTE_COUNT + 0x100) & 0x7fff; >> rmb(); >> >> /* Read the counter values again for verification */ >> - bccrlv = readl(mmio_base + PDC_BYTE_COUNT) & 0xffff; >> - bccrhv = readl(mmio_base + PDC_BYTE_COUNT + 0x100) & 0xffff; >> + bccrlv = readl(mmio_base + PDC_BYTE_COUNT) & 0x7fff; >> + bccrhv = readl(mmio_base + PDC_BYTE_COUNT + 0x100) & 0x7fff; >> rmb(); >> >> counter = (bccrh << 15) | bccrl; > > > Unrelated to your changes, but, I wonder why those rmb() are there at > all...? > The first rmb() is to make sure bccrl is read before bccrlv for later (bccrl >= bccrlv) check since both reading the same memory address. The second rmb() looks like leftover when the code copy-and-paste'ed. Maybe we can remove this one. -- albert - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
