From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-wm0-f46.google.com ([74.125.82.46]:38631 "EHLO mail-wm0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753032AbcKTRhG (ORCPT ); Sun, 20 Nov 2016 12:37:06 -0500 Received: by mail-wm0-f46.google.com with SMTP id f82so109966158wmf.1 for ; Sun, 20 Nov 2016 09:37:05 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20161028085224.GA9826@arch-desktop> References: <20161028085224.GA9826@arch-desktop> From: Ezequiel Garcia Date: Sun, 20 Nov 2016 14:37:04 -0300 Message-ID: Subject: Re: [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec. To: Marcel Hasler Cc: Mauro Carvalho Chehab , linux-media , Hans Verkuil Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: linux-media-owner@vger.kernel.org List-ID: On 28 October 2016 at 05:52, Marcel Hasler wrote: > 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 > --- > drivers/media/usb/stk1160/stk1160-ac97.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/media/usb/stk1160/stk1160-ac97.c b/drivers/media/usb= /stk1160/stk1160-ac97.c > index 31bdd60d..caa65a8 100644 > --- a/drivers/media/usb/stk1160/stk1160-ac97.c > +++ b/drivers/media/usb/stk1160/stk1160-ac97.c > @@ -20,6 +20,7 @@ > * > */ > > +#include > #include > > #include "stk1160.h" > @@ -61,6 +62,9 @@ static u16 stk1160_read_ac97(struct stk1160 *dev, u16 r= eg) > */ > stk1160_write_reg(dev, STK1160_AC97CTL_0, 0x8b); > > + /* Give the chip some time to transfer data */ > + usleep_range(20, 40); > + I don't recall any issues with this. In any case, we only read the register= s for debugging purposes, so it's not a big deal. Maybe it would be better to expand the comment a little bit, using your commit log: "" 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. "" This way, if the sleep proves problematic in the future, the "proper way" is already documented. > /* Retrieve register value */ > stk1160_read_reg(dev, STK1160_AC97_CMD, &vall); > stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh); > -- > 2.10.1 > --=20 Ezequiel Garc=C3=ADa, VanguardiaSur www.vanguardiasur.com.ar