Hi Wolfgang.
On 12/07/11 20:36, Graeme Russ wrote:
> As I said, I will have a closer look at the Linux API...
OK, I've had a look at how the Linux API is used - in particular
time_after(). Here is a typical random example (from drivers/spi/ep93xx_spi.c):
timeout = jiffies + msecs_to_jiffies(SPI_TIMEOUT);
while (ep93xx_spi_read_u16(espi, SSPSR) & SSPSR_RNE) {
if (time_after(jiffies, timeout)) {
dev_warn(&espi->pdev->dev,
"timeout while flushing RX FIFO\n");
msg->status = -ETIMEDOUT;
return;
}
ep93xx_spi_read_u16(espi, SSPDR);
}
Now I personally do not like the global 'jiffies' variable for two reasons:
a) It assumes there is some interrupt source updating jiffies which we
cannot guarantee. The discussions of the new API had the background counter
being update by both a background interrupt (if available) or a call to
get_timer()
b) It has no fixed time base
So it looks like the nanosecond clocksource code and the time_after et al
macros are not directly related (as evidenced by time_after being in jiffies.h)
So maybe we should look at something along the lines of:
timeout = get_ms_count() + SPI_TIMEOUT;
while (ep93xx_spi_read_u16(espi, SSPSR) & SSPSR_RNE) {
if (time_after(get_ms_count(), timeout)) {
dev_warn(&espi->pdev->dev,
"timeout while flushing RX FIFO\n");
msg->status = -ETIMEDOUT;
return;
}
ep93xx_spi_read_u16(espi, SSPDR);
}
The get_ms_count() name is up for debate
So this would mean minimal timer related code conversion bringing drivers
from Linux, and a namespace which does not match Linux that will hence
generate obvious compile errors.
If you really wanted to we could
#define jiffies get_ms_count()
#define msecs_to_jiffies(x) x
But I think that might be dangerous
Now we can use the existing get_timer(0) call (as I already did with this
patch series) now and create the underlying architecture intrusive re-write
of the generic 'clocksource' API later.
And then phase 3 would be to revisit udelay
Regards,
Graeme
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