On Tue, 30 Jan 2007 11:26:42 +0100
Rodolfo Giometti <[email protected]> wrote:
> > > +static int tsl2550_get_adc_value(struct i2c_client *client, int channel)
> > > +{
> > > + u8 cmd = channel == 0 ? TSL2550_READ_ADC0 : TSL2550_READ_ADC1;
> > > + int timeout, ret;
> > > +
> > > + /* Read ADC channel waiting at most 400ms (see data sheet for further
> > > + * info) */
> > > + for (timeout = 400; timeout > 0; timeout--) {
> > > + i2c_smbus_write_byte(client, cmd);
> > > + mdelay(1);
> > > + ret = i2c_smbus_read_byte(client);
> > > + if (ret < 0)
> > > + return ret;
> > > + else if (ret & 0x0080)
> > > + break;
> > > + }
> > > + if (timeout == 0)
> > > + return -EIO;
> > > + return ((u8) ret) & 0x7f; /* remove the "valid" bit */
> > > +}
> >
> > eek. Is there no way to avoid the busy-wait? We cannot sleep here?
>
> That's why I have to retry reading data for at most 400ms otherwise
> the chip will start a new ADC conversion.
>
> I can replace mdelay(1) with schedule_timeout(HZ/1000) but doing this
> I'm not sure that just 1ms has elapesed. Also the chip has no irq
> lines to use for that.
I expect an msleep(1) will be OK, if you can indeed sleep on this
codepath. Yes, that can delay for longer: ten milliseconds for sure
if HZ=100.
If that's a problem I guess you could spin for a millisecond or two, then
start sleeping:
end = jiffies + msecs_to_jiffies(400);
while (time_before(jiffies, end)) {
loop++;
...
if (loop < 5)
mdelay(1);
else
msleep(1);
}
or something like that.
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