Em Sun, 05 Jan 2014 11:20:02 -0200
Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx> escreveu:
> Em Sun, 05 Jan 2014 12:19:41 +0100
> Frank Schäfer <fschaefer.oss@xxxxxxxxxxxxxx> escreveu:
>
> > Am 04.01.2014 11:55, schrieb Mauro Carvalho Chehab:
> > > Instead of assuming that msleep() is precise, use a jiffies
> > > based code to wait for AC97 to be available.
> > >
> > > Signed-off-by: Mauro Carvalho Chehab <m.chehab@xxxxxxxxxxx>
> > > ---
> > > drivers/media/usb/em28xx/em28xx-core.c | 7 +++++--
> > > drivers/media/usb/em28xx/em28xx.h | 5 ++++-
> > > 2 files changed, 9 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/media/usb/em28xx/em28xx-core.c b/drivers/media/usb/em28xx/em28xx-core.c
> > > index 818248d3fd28..36b2f1ab4474 100644
> > > --- a/drivers/media/usb/em28xx/em28xx-core.c
> > > +++ b/drivers/media/usb/em28xx/em28xx-core.c
> > > @@ -23,6 +23,7 @@
> > > */
> > >
> > > #include <linux/init.h>
> > > +#include <linux/jiffies.h>
> > > #include <linux/list.h>
> > > #include <linux/module.h>
> > > #include <linux/slab.h>
> > > @@ -254,16 +255,18 @@ EXPORT_SYMBOL_GPL(em28xx_toggle_reg_bits);
> > > */
> > > static int em28xx_is_ac97_ready(struct em28xx *dev)
> > > {
> > > - int ret, i;
> > > + unsigned long timeout = jiffies + msecs_to_jiffies(EM2800_AC97_XFER_TIMEOUT);
> > > + int ret;
> > >
> > > /* Wait up to 50 ms for AC97 command to complete */
> > > - for (i = 0; i < 10; i++, msleep(5)) {
> > > + while (time_is_after_jiffies(timeout)) {
> > time_is_before_jiffies(timeout)
> >
> > > ret = em28xx_read_reg(dev, EM28XX_R43_AC97BUSY);
> > > if (ret < 0)
> > > return ret;
> > >
> > > if (!(ret & 0x01))
> > > return 0;
> > > + msleep (5);
> > > }
> > >
> > > em28xx_warn("AC97 command still being executed: not handled properly!\n");
> > > diff --git a/drivers/media/usb/em28xx/em28xx.h b/drivers/media/usb/em28xx/em28xx.h
> > > index 9d6f43e4681f..ac79501f5d9f 100644
> > > --- a/drivers/media/usb/em28xx/em28xx.h
> > > +++ b/drivers/media/usb/em28xx/em28xx.h
> > > @@ -182,9 +182,12 @@
> > >
> > > #define EM28XX_INTERLACED_DEFAULT 1
> > >
> > > -/* time in msecs to wait for i2c writes to finish */
> > > +/* time in msecs to wait for i2c xfers to finish */
> > > #define EM2800_I2C_XFER_TIMEOUT 20
> > >
> > > +/* time in msecs to wait for AC97 xfers to finish */
> > > +#define EM2800_AC97_XFER_TIMEOUT 100
> > > +
> > I applies to all chips supporting AC97 audio, so call it
> > EM28XX_AC97_XFER_TIMEOUT.
>
> Ok.
>
> > Why did you increase the timeout from 50ms to 100ms ?
> > 50ms already seems to be a lot !
Err... actually, the code is currently waiting for up to 100ms.
The thing is that msleep(5) will wait for a minimum time of 1/CONFIG_HZ.
If CONFIG_HZ is equal to 100 (the minimum), that means that it will
wait for 10 ms. So,
for (i = 0; i < 10; i++, msleep(5)) {
...
}
Will actually wait up to 10*10ms = 100ms at the worse case.
The patch is just keeping the maximum timeout equal for all setups, no
matter what's set at CONFIG_HZ.
Arbitrarily changing it to a lower value seems risky, as it may cause
regressions on some boards.
So, I'll just rename the define here, preserving 100ms as timeout.
Regards,
Mauro
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