On Thu, 17 Apr 2008 18:05:32 +0200, Wolfram Sang wrote:
> Greetings,
>
> (this goes mostly to David, I assume)
>
> In at24_ee_write:
> > + /* Writes fail if the previous one didn't complete yet. We'll
> > + * loop a few times until this one succeeds, waiting at least
> > + * long enough for one entire page write to work.
> > + */
> > + timeout = jiffies + msecs_to_jiffies(AT24_EE_TIMEOUT);
> > + for (retries = 0; retries < 3; retries++) {
> > +
> > + if (at24->use_smbus) {
> > + status = i2c_smbus_write_i2c_block_data(client,
> > + offset, count, buf);
> > + if (status == 0)
> > + status = count;
> > + } else {
> > + status = i2c_transfer(client->adapter, &msg, 1);
> > + if (status == 1)
> > + status = count;
> > + }
> > + dev_dbg(&client->dev, "write [EMAIL PROTECTED] --> %zd (%ld)\n",
> > + count, offset, status, jiffies);
> > +
> > + if (status == count)
> > + return count;
> > +
> > + if (retries < 3 || time_after(timeout, jiffies)) {
> > + /* REVISIT: at HZ=100, this is sloooow */
> > + msleep(1);
> > + continue;
> > + }
> > + }
> I assume 'retries < 3' (always true) and 'continue' (nothing follows)
> are left-overs from earlier revisions and can be thrown out? My main
> questions is 'msleep(1)' though: As I understand it, this means the
> for-loop will wait roughly 3ms on failures until it reports a timeout
> (assuming good precision of msleep). Comparing this to AT24_EE_TIMEOUT
> (25 ms), it looks to me that the msleep value could be increased a
> little (maybe to AT24_EE_TIMEOUT / 3)? Or is i2c_transfer slow enough
> and can we count on that behaviour?
msleep() can't sleep less than one jiffie, so msleep(1) is the same as
msleep(10) at HZ=100. At HZ=1000, msleep(1) is almost possible,
although it might sleep for up to 2 ms in practice (finish the current
jiffie + the next jiffie.)
The bottom line is that you never really know how much msleep(N)
will sleep for small values of N.
I realize that it doesn't really answer your question, but that's still
worth keeping in mind.
--
Jean Delvare
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