* [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec. @ 2016-10-28 8:52 Marcel Hasler [not found] ` <CAOJOY2MwyX++KbGLBXpf5nKihmrP+Qx5JgYJ==q-41t-znVwKQ@mail.gmail.com> 2016-11-20 17:37 ` Ezequiel Garcia 0 siblings, 2 replies; 5+ messages in thread From: Marcel Hasler @ 2016-10-28 8:52 UTC (permalink / raw) To: Ezequiel Garcia, Mauro Carvalho Chehab; +Cc: linux-media 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@gmail.com> --- 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 <linux/delay.h> #include <linux/module.h> #include "stk1160.h" @@ -61,6 +62,9 @@ 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 data */ + usleep_range(20, 40); + /* Retrieve register value */ stk1160_read_reg(dev, STK1160_AC97_CMD, &vall); stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh); -- 2.10.1 ^ permalink raw reply related [flat|nested] 5+ messages in thread
[parent not found: <CAOJOY2MwyX++KbGLBXpf5nKihmrP+Qx5JgYJ==q-41t-znVwKQ@mail.gmail.com>]
* Fwd: [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec. [not found] ` <CAOJOY2MwyX++KbGLBXpf5nKihmrP+Qx5JgYJ==q-41t-znVwKQ@mail.gmail.com> @ 2016-10-28 10:39 ` Marcel Hasler 0 siblings, 0 replies; 5+ messages in thread From: Marcel Hasler @ 2016-10-28 10:39 UTC (permalink / raw) Cc: linux-media This patch might need some explaining. I actually noticed this problem early on while trying to fix the sound problem, but it was only this morning that I realized the (trivial) cause of it. I first noticed something strange going on when I read the AC97 registers from /proc/asound/cardX/codec97#0/ac97#0-0+regs using the current version of the driver. Every time I read that file I would get slightly different values, not only for one register but for several of them. Also, every time I plugged in the device and opened alsamixer I would be presented with a different set of mixer controls. So obviously something was going wrong while talking to the AC97 chip. When analyzing the USB trace I took from Windows (on VirtualBox) I found long delays (2 ms) between control packets and wondered whether those might be set by the driver on purpose. So I tried adding delays in stk1160_[read|write]_reg, and sure enough, the problem disappeared. In retrospective I suspect those long delays to really be the result of virtualization overhead. I actually tried getting a native trace using USBpcap, but unfortunately its timer resolution is so low that it's impossible to get any useful data. Once I realized what the actual problem was I removed the delays in stk1160_[read|write]_reg and instead experimented with different delays in stk1160_read_ac97 and found 20 us to be perfectly sufficient to get reliable reads. Now the strange thing about this problem is that it occurs on both of my notebooks, but not on my desktop computer. I can only speculate about the reason for this. My theory is that is has something to do with the way different USB host controllers handle/buffer outgoing control packets. Both of my notebooks are recent models by Acer (a normal notebook and a cloudbook) and most likely use the same host controller. My desktop motherboard on the other hand is a bit older. So I wonder, have you experienced this problem on your own systems? Best regards Marcel 2016-10-28 10:52 GMT+02:00 Marcel Hasler <mahasler@gmail.com>: > 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@gmail.com> > --- > 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 <linux/delay.h> > #include <linux/module.h> > > #include "stk1160.h" > @@ -61,6 +62,9 @@ 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 data */ > + usleep_range(20, 40); > + > /* Retrieve register value */ > stk1160_read_reg(dev, STK1160_AC97_CMD, &vall); > stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh); > -- > 2.10.1 > ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec. 2016-10-28 8:52 [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec Marcel Hasler [not found] ` <CAOJOY2MwyX++KbGLBXpf5nKihmrP+Qx5JgYJ==q-41t-znVwKQ@mail.gmail.com> @ 2016-11-20 17:37 ` Ezequiel Garcia 2016-11-26 13:59 ` Marcel Hasler 2016-11-26 14:07 ` Marcel Hasler 1 sibling, 2 replies; 5+ messages in thread From: Ezequiel Garcia @ 2016-11-20 17:37 UTC (permalink / raw) To: Marcel Hasler; +Cc: Mauro Carvalho Chehab, linux-media, Hans Verkuil On 28 October 2016 at 05:52, Marcel Hasler <mahasler@gmail.com> 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 <mahasler@gmail.com> > --- > 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 <linux/delay.h> > #include <linux/module.h> > > #include "stk1160.h" > @@ -61,6 +62,9 @@ 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 data */ > + usleep_range(20, 40); > + I don't recall any issues with this. In any case, we only read the registers 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 > -- Ezequiel García, VanguardiaSur www.vanguardiasur.com.ar ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec. 2016-11-20 17:37 ` Ezequiel Garcia @ 2016-11-26 13:59 ` Marcel Hasler 2016-11-26 14:07 ` Marcel Hasler 1 sibling, 0 replies; 5+ messages in thread From: Marcel Hasler @ 2016-11-26 13:59 UTC (permalink / raw) To: Ezequiel Garcia; +Cc: Mauro Carvalho Chehab, linux-media, Hans Verkuil 2016-11-20 18:37 GMT+01:00 Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>: > On 28 October 2016 at 05:52, Marcel Hasler <mahasler@gmail.com> 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 <mahasler@gmail.com> >> --- >> 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 <linux/delay.h> >> #include <linux/module.h> >> >> #include "stk1160.h" >> @@ -61,6 +62,9 @@ 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 data */ >> + usleep_range(20, 40); >> + > > I don't recall any issues with this. In any case, we only read the registers > 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. > Of course, since the register dump isn't needed anymore, this function could also be dropped. But then again, I think it would make sense to keep it, even if it's just for documentation. There might be use for it in the future. I'll add a comment as suggested. Let me know whether I should remove the dump, I guess there's no need to keep it. I'll then prepare a new patchset with all four patches as soon as I can. >> /* Retrieve register value */ >> stk1160_read_reg(dev, STK1160_AC97_CMD, &vall); >> stk1160_read_reg(dev, STK1160_AC97_CMD + 1, &valh); >> -- >> 2.10.1 >> > > > > -- > Ezequiel García, VanguardiaSur > www.vanguardiasur.com.ar Best regards Marcel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec. 2016-11-20 17:37 ` Ezequiel Garcia 2016-11-26 13:59 ` Marcel Hasler @ 2016-11-26 14:07 ` Marcel Hasler 1 sibling, 0 replies; 5+ messages in thread From: Marcel Hasler @ 2016-11-26 14:07 UTC (permalink / raw) To: Ezequiel Garcia; +Cc: Mauro Carvalho Chehab, linux-media, Hans Verkuil 2016-11-20 18:37 GMT+01:00 Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>: > On 28 October 2016 at 05:52, Marcel Hasler <mahasler@gmail.com> 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 <mahasler@gmail.com> >> --- >> 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 <linux/delay.h> >> #include <linux/module.h> >> >> #include "stk1160.h" >> @@ -61,6 +62,9 @@ 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 data */ >> + usleep_range(20, 40); >> + > > I don't recall any issues with this. In any case, we only read the registers > for debugging purposes, so it's not a big deal. > I actually just re-tested this, as I recently replaced my computer's main board. I didn't happen with my old one, but it does with my new one, just as with both of my notebooks. > 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 >> > > > > -- > Ezequiel García, VanguardiaSur > www.vanguardiasur.com.ar ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2016-11-26 14:07 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2016-10-28 8:52 [PATCH] stk1160: Give the chip some time to retrieve data from AC97 codec Marcel Hasler [not found] ` <CAOJOY2MwyX++KbGLBXpf5nKihmrP+Qx5JgYJ==q-41t-znVwKQ@mail.gmail.com> 2016-10-28 10:39 ` Fwd: " Marcel Hasler 2016-11-20 17:37 ` Ezequiel Garcia 2016-11-26 13:59 ` Marcel Hasler 2016-11-26 14:07 ` Marcel Hasler
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