Re: [PATCH 1/1] libata: pata_pdc2027x PLL input clock fix

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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:

<snip>

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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.
--
albert

(BTW, maybe opening a bug in bugzilla.kernel.org would help the
debugging.)

--- 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);