Em Sun, 27 Nov 2016 12:12:36 +0100 Marcel Hasler <mahasler@xxxxxxxxx> escreveu: > The STK1160 needs some time to transfer data from the AC97 registers into its own. On some > systems reading the chip's own registers to soon will return wrong values. The "proper" way to > handle this would be to poll STK1160_AC97CTL_0 after every read or write command until the > command bit has been cleared, but this may not be worth the hassle. > > Signed-off-by: Marcel Hasler <mahasler@xxxxxxxxx> > --- > drivers/media/usb/stk1160/stk1160-ac97.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/drivers/media/usb/stk1160/stk1160-ac97.c b/drivers/media/usb/stk1160/stk1160-ac97.c > index 60327af..b39f51b 100644 > --- a/drivers/media/usb/stk1160/stk1160-ac97.c > +++ b/drivers/media/usb/stk1160/stk1160-ac97.c > @@ -23,6 +23,7 @@ > * > */ > > +#include <linux/delay.h> > #include <linux/module.h> > > #include "stk1160.h" > @@ -64,6 +65,14 @@ static u16 stk1160_read_ac97(struct stk1160 *dev, u16 reg) > */ > stk1160_write_reg(dev, STK1160_AC97CTL_0, 0x8b); > > + /* > + * Give the chip some time to transfer the data. > + * The proper way would be to poll STK1160_AC97CTL_0 > + * until the command bit has been cleared, but this > + * may not be worth the hassle. Why not? Relying on a fixed amount time is not nice. Take a look at em28xx_is_ac97_ready() function, at drivers/media/usb/em28xx/em28xx-core.c to see how this could be implemented instead. > + */ > + usleep_range(20, 40); > + > /* Retrieve register value */ > stk1160_read_reg(dev, STK1160_AC97_CMD, &vall); > stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh); Thanks, Mauro -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
