diff mbox

[v4,12/22,media] em28xx: properly implement AC97 wait code

Message ID 1388832951-11195-13-git-send-email-m.chehab@samsung.com (mailing list archive)
State New, archived
Headers show

Commit Message

Mauro Carvalho Chehab Jan. 4, 2014, 10:55 a.m. UTC 
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@samsung.com>
---
 drivers/media/usb/em28xx/em28xx-core.c | 7 +++++--
 drivers/media/usb/em28xx/em28xx.h      | 5 ++++-
 2 files changed, 9 insertions(+), 3 deletions(-)

Comments

Frank Schäfer Jan. 5, 2014, 11:19 a.m. UTC | #1 
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@samsung.com>
> ---
>  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.

Why did you increase the timeout from 50ms to 100ms ?
50ms already seems to be a lot !

IIRC, the problem you are trying to fix is that the chip sometimes is
not yet ready when probing.
But that should be solved with a single sleep before accessing the AC97
chip for the first time instead ?!

>  /* max. number of button state polling addresses */
>  #define EM28XX_NUM_BUTTON_ADDRESSES_MAX		5
>  

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Mauro Carvalho Chehab Jan. 5, 2014, 1:20 p.m. UTC | #2 
Em Sun, 05 Jan 2014 12:19:41 +0100
Frank Schäfer <fschaefer.oss@googlemail.com> 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@samsung.com>
> > ---
> >  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 !
> 
> IIRC, the problem you are trying to fix is that the chip sometimes is
> not yet ready when probing.

Yes. I was also hoping that would make the code more reliable, as
there are some issues with audio here (with usb 3.0 and with xawtv
when trying to maximize the window).

> But that should be solved with a single sleep before accessing the AC97
> chip for the first time instead ?!

Maybe. I'll try it.

> >  /* max. number of button state polling addresses */
> >  #define EM28XX_NUM_BUTTON_ADDRESSES_MAX		5
> >  
>
Mauro Carvalho Chehab Jan. 5, 2014, 3:44 p.m. UTC | #3 
Em Sun, 05 Jan 2014 11:20:02 -0200
Mauro Carvalho Chehab <m.chehab@samsung.com> escreveu:

> Em Sun, 05 Jan 2014 12:19:41 +0100
> Frank Schäfer <fschaefer.oss@googlemail.com> 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@samsung.com>
> > > ---
> > >  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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Frank Schäfer Jan. 7, 2014, 4:50 p.m. UTC | #4 
Am 05.01.2014 16:44, schrieb Mauro Carvalho Chehab:
> Em Sun, 05 Jan 2014 11:20:02 -0200
> Mauro Carvalho Chehab <m.chehab@samsung.com> escreveu:
>
>> Em Sun, 05 Jan 2014 12:19:41 +0100
>> Frank Schäfer <fschaefer.oss@googlemail.com> 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@samsung.com>
>>>> ---
>>>>  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
Ok, then it makes sense.
I'm pretty sure 100ms is much more than needed and it seems to work for
those people using a CONFIG_HZ value higher 100.
But for now let's keep it as.

Reviewed-by: Frank Schäfer <fschaefer.oss@googlemail.com>


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diff mbox

Patch

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)) {
 		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
+
 /* max. number of button state polling addresses */
 #define EM28XX_NUM_BUTTON_ADDRESSES_MAX		5