On 2 December 2016 at 08:09, Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxxx> wrote: > 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. > We were reluctant to implement this properly because the read reg function is only used for debugging purposes, to dump registers. That said, it's not too much of a hassle to do it properly, and we might have to if we are going to have our own mixer. > >> + */ >> + 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 -- Ezequiel García, VanguardiaSur www.vanguardiasur.com.ar -- 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
