[PATCH 1/1] libata: pata_pdc2027x PLL input clock fix
mikpe at it.uu.se
Wed Jul 11 09:14:32 EST 2007
On Tue, 10 Jul 2007 11:52:59 +0800, Albert Lee wrote:
> >>Recently the PLL input clock of pata_pdc2027x is sometimes detected
> >>higer than expected (e.g. 20.027 MHz compared to 16.714 MHz).
> >>It seems sometimes the mdelay() function is not as precise as it
> >>used to be. Per Alan's advice, HT or power management might affect
> >>the precision of mdelay().
> >>This patch calls gettimeofday() to mesure the time elapsed and
> >>calculate the PLL input clock accordingly.
> > Unfortunately this breaks pata_pdc2027x on my PowerMac G3:
> > In fairness, this is a slightly non-standard PowerMac G3, in that it
> > has a G4 upgrade processor. The firmware doesn't recognise the CPU
> > and gives some CPU core frequency-related properties too low values.
> > However, the bus frequency property _is_ correct, which is what
> > most or all timing stuff should be based on.
> > Looks like a platform bug.
> According to the document, do_gettimeofday() has microsecond
> resolution. Since the driver calls mdelay(100) (100000 microseconds),
> it won't affect the PLL input clock calculation much if somehow
> do_gettimeofday() drifts several (say 100) microseconds.
> Could you please apply the attached debug patch and collect more info
> on the PowerMac G3. Hopefully we can have more clue. Thanks.
> (BTW, maybe opening a bug in bugzilla.kernel.org would help the
> --- 00_libata-dev/drivers/ata/pata_pdc2027x.c 2007-07-07 09:58:55.000000000 +0800
> +++ 01_debug/drivers/ata/pata_pdc2027x.c 2007-07-10 11:18:38.000000000 +0800
> @@ -722,6 +722,15 @@ static long pdc_detect_pll_input_clock(s
> pll_clock = (start_count - end_count) / 100 *
> (100000000 / usec_elapsed);
> + do_gettimeofday(&start_time);
> + mdelay(37);
> + do_gettimeofday(&end_time);
> + usec_elapsed = (end_time.tv_sec - start_time.tv_sec) * 1000000 +
> + (end_time.tv_usec - start_time.tv_usec);
> + printk(KERN_ERR "usec_elapsed for mdelay(37) [%ld]\n", usec_elapsed);
> + printk(KERN_ERR "start time: [%ld]s [%ld]us \n", start_time.tv_sec, start_time.tv_usec);
> + printk(KERN_ERR "end time: [%ld]s [%ld]us \n", end_time.tv_sec, end_time.tv_usec);
> PDPRINTK("start[%ld] end[%ld] \n", start_count, end_count);
> PDPRINTK("PLL input clock[%ld]Hz\n", pll_clock);
2.6.22 + this prints the following on my G3:
pata_pdc2027x 0000:00:0e.0: version 0.9
usec_elapsed for mdelay(37) 
start time: s us
end time: s us
pata_pdc2027x 0000:00:0e.0: PLL input clock 1691741 kHz
pata_pdc2027x: Invalid PLL input clock 1691741kHz, give up!
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