[alsa-devel] [PATCH 15/27] ALSA: hda - Use timecounter_initialize interface
With new interface timecounter_initialize we can initialize timecounter fields and underlying cyclecounter together. Update azx timecounter init with this new function.
Signed-off-by: Sagar Arun Kamble sagar.a.kamble@intel.com Cc: Richard Cochran richardcochran@gmail.com Cc: Jaroslav Kysela perex@perex.cz Cc: Takashi Iwai tiwai@suse.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vinod Koul vinod.koul@intel.com Cc: alsa-devel@alsa-project.org Cc: linux-kernel@vger.kernel.org --- sound/hda/hdac_stream.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/sound/hda/hdac_stream.c b/sound/hda/hdac_stream.c index 9426c1a..ad91dde 100644 --- a/sound/hda/hdac_stream.c +++ b/sound/hda/hdac_stream.c @@ -477,12 +477,8 @@ static void azx_timecounter_init(struct hdac_stream *azx_dev, bool force, u64 last) { struct timecounter *tc = &azx_dev->tc; - struct cyclecounter *cc = &azx_dev->tc.cc; u64 nsec;
- cc->read = azx_cc_read; - cc->mask = CLOCKSOURCE_MASK(32); - /* * Converting from 24 MHz to ns means applying a 125/3 factor. * To avoid any saturation issues in intermediate operations, @@ -493,11 +489,13 @@ static void azx_timecounter_init(struct hdac_stream *azx_dev, * overflows occur after about 4 hours or less, not a option. */
- cc->mult = 125; /* saturation after 195 years */ - cc->shift = 0; - nsec = 0; /* audio time is elapsed time since trigger */ - timecounter_init(tc, nsec); + timecounter_initialize(tc, + azx_cc_read, + CLOCKSOURCE_MASK(32), + 125, /* saturation after 195 years */ + 0, + nsec); if (force) { /* * force timecounter to use predefined value,
On Fri, 15 Dec 2017 08:38:30 +0100, Sagar Arun Kamble wrote:
With new interface timecounter_initialize we can initialize timecounter fields and underlying cyclecounter together. Update azx timecounter init with this new function.
Signed-off-by: Sagar Arun Kamble sagar.a.kamble@intel.com Cc: Richard Cochran richardcochran@gmail.com Cc: Jaroslav Kysela perex@perex.cz Cc: Takashi Iwai tiwai@suse.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vinod Koul vinod.koul@intel.com Cc: alsa-devel@alsa-project.org Cc: linux-kernel@vger.kernel.org
sound/hda/hdac_stream.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/sound/hda/hdac_stream.c b/sound/hda/hdac_stream.c index 9426c1a..ad91dde 100644 --- a/sound/hda/hdac_stream.c +++ b/sound/hda/hdac_stream.c @@ -477,12 +477,8 @@ static void azx_timecounter_init(struct hdac_stream *azx_dev, bool force, u64 last) { struct timecounter *tc = &azx_dev->tc;
struct cyclecounter *cc = &azx_dev->tc.cc; u64 nsec;
cc->read = azx_cc_read;
cc->mask = CLOCKSOURCE_MASK(32);
/*
- Converting from 24 MHz to ns means applying a 125/3 factor.
- To avoid any saturation issues in intermediate operations,
@@ -493,11 +489,13 @@ static void azx_timecounter_init(struct hdac_stream *azx_dev, * overflows occur after about 4 hours or less, not a option. */
- cc->mult = 125; /* saturation after 195 years */
- cc->shift = 0;
- nsec = 0; /* audio time is elapsed time since trigger */
- timecounter_init(tc, nsec);
- timecounter_initialize(tc,
azx_cc_read,CLOCKSOURCE_MASK(32),125, /* saturation after 195 years */0,nsec);
Hmm, a function with so many arguments is difficult to remember and is often error-prone. By this transition, it becomes harder to read through.
thanks,
Takashi
On Fri, Dec 15, 2017 at 12:10:47PM +0100, Takashi Iwai wrote:
- struct cyclecounter *cc = &azx_dev->tc.cc;
- cc->read = azx_cc_read;
- cc->mask = CLOCKSOURCE_MASK(32);
- cc->mult = 125; /* saturation after 195 years */
- cc->shift = 0;
I want to get away from this mess of open coded structure initialization and use a proper functional interface instead.
nsec = 0; /* audio time is elapsed time since trigger */
- timecounter_init(tc, nsec);
- timecounter_initialize(tc,
azx_cc_read,CLOCKSOURCE_MASK(32),125, /* saturation after 195 years */0,nsec);Hmm, a function with so many arguments is difficult to remember and is often error-prone. By this transition, it becomes harder to read through.
Please suggest a better way.
Thanks, Richard
On Fri, 15 Dec 2017 17:51:25 +0100, Richard Cochran wrote:
On Fri, Dec 15, 2017 at 12:10:47PM +0100, Takashi Iwai wrote:
- struct cyclecounter *cc = &azx_dev->tc.cc;
- cc->read = azx_cc_read;
- cc->mask = CLOCKSOURCE_MASK(32);
- cc->mult = 125; /* saturation after 195 years */
- cc->shift = 0;
I want to get away from this mess of open coded structure initialization and use a proper functional interface instead.
I agree that a proper functional interface would be better, too. But not a form like foo(501, 21, 10, 499, 5678). In C syntax, you may more easily pass a wrong value than open codes.
nsec = 0; /* audio time is elapsed time since trigger */
- timecounter_init(tc, nsec);
- timecounter_initialize(tc,
azx_cc_read,CLOCKSOURCE_MASK(32),125, /* saturation after 195 years */0,nsec);Hmm, a function with so many arguments is difficult to remember and is often error-prone. By this transition, it becomes harder to read through.
Please suggest a better way.
I have no good idea ATM, sorry.
Or can we provide simpler versions for covering some defaults? At least reducing the number of arguments would make things easier.
Takashi
On 12/15/2017 10:40 PM, Takashi Iwai wrote:
On Fri, 15 Dec 2017 17:51:25 +0100, Richard Cochran wrote:
On Fri, Dec 15, 2017 at 12:10:47PM +0100, Takashi Iwai wrote:
- struct cyclecounter *cc = &azx_dev->tc.cc;
- cc->read = azx_cc_read;
- cc->mask = CLOCKSOURCE_MASK(32);
- cc->mult = 125; /* saturation after 195 years */
- cc->shift = 0;
I want to get away from this mess of open coded structure initialization and use a proper functional interface instead.
I agree that a proper functional interface would be better, too. But not a form like foo(501, 21, 10, 499, 5678). In C syntax, you may more easily pass a wrong value than open codes.
nsec = 0; /* audio time is elapsed time since trigger */
- timecounter_init(tc, nsec);
- timecounter_initialize(tc,
azx_cc_read,CLOCKSOURCE_MASK(32),125, /* saturation after 195 years */0,nsec);Hmm, a function with so many arguments is difficult to remember and is often error-prone. By this transition, it becomes harder to read through.
Please suggest a better way.
I have no good idea ATM, sorry.
Or can we provide simpler versions for covering some defaults? At least reducing the number of arguments would make things easier.
Thought about specifying 1. cyclecounter read func 2. frequency 3. width of counter as parameters here which can get rid of mult, shift params. But this is not easy as most of the drivers do not specify cyclecounter frequency and instead hard-code the mult/shift factors. How about passing initialized cyclecounter struct?
Takashi
On Tue, Dec 26, 2017 at 01:07:35PM +0530, Sagar Arun Kamble wrote:
Or can we provide simpler versions for covering some defaults? At least reducing the number of arguments would make things easier.
Thought about specifying 1. cyclecounter read func 2. frequency 3. width of counter as parameters here which can get rid of mult, shift params. But this is not easy as most of the drivers do not specify cyclecounter frequency and instead hard-code the mult/shift factors.
You are talking about using clocks_calc_mult_shift() here, right? (See the usage example in drivers/net/ethernet/ti/cpts.c).
This is a good idea, and it is worth getting the driver authors' input to figure out the correct parameters.
I bet we can use that almost everywhere. If there are any drivers that cannot be converted, then we can leave some sort of low level legacy initialization method.
Thanks, Richard
On 12/28/2017 10:19 PM, Richard Cochran wrote:
On Tue, Dec 26, 2017 at 01:07:35PM +0530, Sagar Arun Kamble wrote:
Or can we provide simpler versions for covering some defaults? At least reducing the number of arguments would make things easier.
Thought about specifying 1. cyclecounter read func 2. frequency 3. width of counter as parameters here which can get rid of mult, shift params. But this is not easy as most of the drivers do not specify cyclecounter frequency and instead hard-code the mult/shift factors.
You are talking about using clocks_calc_mult_shift() here, right? (See the usage example in drivers/net/ethernet/ti/cpts.c).
Yes
This is a good idea, and it is worth getting the driver authors' input to figure out the correct parameters.
I bet we can use that almost everywhere. If there are any drivers that cannot be converted, then we can leave some sort of low level legacy initialization method.
Agree
Thanks, Richard
On 1/2/18 12:03 AM, Sagar Arun Kamble wrote:
On 12/28/2017 10:19 PM, Richard Cochran wrote:
On Tue, Dec 26, 2017 at 01:07:35PM +0530, Sagar Arun Kamble wrote:
Or can we provide simpler versions for covering some defaults? At least reducing the number of arguments would make things easier.
Thought about specifying 1. cyclecounter read func 2. frequency 3. width of counter as parameters here which can get rid of mult, shift params. But this is not easy as most of the drivers do not specify cyclecounter frequency and instead hard-code the mult/shift factors.
You are talking about using clocks_calc_mult_shift() here, right? (See the usage example in drivers/net/ethernet/ti/cpts.c).
Yes
This is a good idea, and it is worth getting the driver authors' input to figure out the correct parameters.
I wrote the code for HDaudio and I remember wasting time trying to figure out the gory details of the cycle counter stuff when all I wanted was a conversion from a 24MHz counter to ns values using a 125/3 operation in the right order - as explained in the comments
If there was a helper to set those mult/shift values it'd make the HDaudio code clearer (and also help support newer modes of operation with a 12 and 6 MHz MCLK).
The initial proposal with hard-coded values in arguments instead of structure members didn't really make the code clearer.
I bet we can use that almost everywhere. If there are any drivers that cannot be converted, then we can leave some sort of low level legacy initialization method.
Agree
Thanks, Richard
Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
On Tue, Jan 02, 2018 at 11:15:45AM -0600, Pierre-Louis Bossart wrote:
I wrote the code for HDaudio and I remember wasting time trying to figure out the gory details of the cycle counter stuff when all I wanted was a conversion from a 24MHz counter to ns values using a 125/3 operation in the right order - as explained in the comments
Would using clocks_calc_mult_shift() work for you?
Thanks, Richard
On 1/2/18 12:21 PM, Richard Cochran wrote:
On Tue, Jan 02, 2018 at 11:15:45AM -0600, Pierre-Louis Bossart wrote:
I wrote the code for HDaudio and I remember wasting time trying to figure out the gory details of the cycle counter stuff when all I wanted was a conversion from a 24MHz counter to ns values using a 125/3 operation in the right order - as explained in the comments
Would using clocks_calc_mult_shift() work for you?
In theory yes, but I'd need to re-check what the results would be. I remember applying the 1/3 factor separately to avoid wrap-around after 4 hours [1], but I can't remember the details on the analysis. I can't figure out what the 'maxsec' argument should be either.
[1] http://elixir.free-electrons.com/linux/latest/source/sound/hda/hdac_stream.c...
On 1/3/2018 1:23 AM, Pierre-Louis Bossart wrote:
On 1/2/18 12:21 PM, Richard Cochran wrote:
On Tue, Jan 02, 2018 at 11:15:45AM -0600, Pierre-Louis Bossart wrote:
I wrote the code for HDaudio and I remember wasting time trying to figure out the gory details of the cycle counter stuff when all I wanted was a conversion from a 24MHz counter to ns values using a 125/3 operation in the right order - as explained in the comments
Would using clocks_calc_mult_shift() work for you?
In theory yes, but I'd need to re-check what the results would be. I remember applying the 1/3 factor separately to avoid wrap-around after 4 hours [1], but I can't remember the details on the analysis. I can't figure out what the 'maxsec' argument should be either.
I am not sure if I understood the wrap-around correctly. Is AZX_REG_WALL_CLK 64bit or 32bit and in the comments which 20 bits are being referred.
Keeping maxsec at lower value will ensure good precision but the mult factor derived then might lead to overflow if the interval of counter read is big. Keeping maxsec high will reduce the mult factor and will marginally impact the precision (of the order of 6 decimal places of fraction nano second).
For 24mhz clock I am getting following scale factors at different maxsec values. I think these are as good as 125/3 125/3 gives scale factor of 41.666666666666666666666666666667
maxsec, mult, shift, scale factor (mult/(2^shift)) 0, 2796202667, 26, 41.66666667163372039794921875 3600, 87381333, 21, 41.666666507720947265625 14400, 21845333, 19, 41.6666660308837890625
I see sound driver uses only timecounter_read so conversions should be fine. If there are usages of timecounter_cyc2time then we will have to take care of updating the timecounter often as timecounter API internally counts time backwards if counter is spaced more than 1/2 the range.
Thanks Sagar
[1] http://elixir.free-electrons.com/linux/latest/source/sound/hda/hdac_stream.c...
On 1/5/18 4:06 AM, Sagar Arun Kamble wrote:
On 1/3/2018 1:23 AM, Pierre-Louis Bossart wrote:
On 1/2/18 12:21 PM, Richard Cochran wrote:
On Tue, Jan 02, 2018 at 11:15:45AM -0600, Pierre-Louis Bossart wrote:
I wrote the code for HDaudio and I remember wasting time trying to figure out the gory details of the cycle counter stuff when all I wanted was a conversion from a 24MHz counter to ns values using a 125/3 operation in the right order - as explained in the comments
Would using clocks_calc_mult_shift() work for you?
In theory yes, but I'd need to re-check what the results would be. I remember applying the 1/3 factor separately to avoid wrap-around after 4 hours [1], but I can't remember the details on the analysis. I can't figure out what the 'maxsec' argument should be either.
I am not sure if I understood the wrap-around correctly. Is AZX_REG_WALL_CLK 64bit or 32bit and in the comments which 20 bits are being referred.
it's a 32-bit counter. off the top of my head, the idea was that the integer arithmetic should not degrade the precision (42ns) and that means you need to be careful with the fractional part, especially if the errors with the fractional part accumulate over time (I think this was the case when I looked several years ago). That's the main reason why I did the division by 3 last, after the read, so that the precision is not impacted by the interval between two reads.
You also need to be careful with the multiplication factor otherwise you will exceed the 64-bit resolution. For example with the 14400 factor, you cannot handle a counter larger than 2^64/14400, which gives you 14826 hours or 1.69 years. It's one of those 'nobody will ever need more than 640KB' value. The 125 factor gives you 195 years without saturating.
Keeping maxsec at lower value will ensure good precision but the mult factor derived then might lead to overflow if the interval of counter read is big. Keeping maxsec high will reduce the mult factor and will marginally impact the precision (of the order of 6 decimal places of fraction nano second).
For 24mhz clock I am getting following scale factors at different maxsec values. I think these are as good as 125/3 125/3 gives scale factor of 41.666666666666666666666666666667
maxsec, mult, shift, scale factor (mult/(2^shift)) 0, 2796202667, 26, 41.66666667163372039794921875 3600, 87381333, 21, 41.666666507720947265625 14400, 21845333, 19, 41.6666660308837890625
I see sound driver uses only timecounter_read so conversions should be fine. If there are usages of timecounter_cyc2time then we will have to take care of updating the timecounter often as timecounter API internally counts time backwards if counter is spaced more than 1/2 the range.
Thanks Sagar
[1] http://elixir.free-electrons.com/linux/latest/source/sound/hda/hdac_stream.c...
On 1/5/2018 9:13 PM, Pierre-Louis Bossart wrote:
On 1/5/18 4:06 AM, Sagar Arun Kamble wrote:
On 1/3/2018 1:23 AM, Pierre-Louis Bossart wrote:
On 1/2/18 12:21 PM, Richard Cochran wrote:
On Tue, Jan 02, 2018 at 11:15:45AM -0600, Pierre-Louis Bossart wrote:
I wrote the code for HDaudio and I remember wasting time trying to figure out the gory details of the cycle counter stuff when all I wanted was a conversion from a 24MHz counter to ns values using a 125/3 operation in the right order - as explained in the comments
Would using clocks_calc_mult_shift() work for you?
In theory yes, but I'd need to re-check what the results would be. I remember applying the 1/3 factor separately to avoid wrap-around after 4 hours [1], but I can't remember the details on the analysis. I can't figure out what the 'maxsec' argument should be either.
I am not sure if I understood the wrap-around correctly. Is AZX_REG_WALL_CLK 64bit or 32bit and in the comments which 20 bits are being referred.
it's a 32-bit counter. off the top of my head, the idea was that the integer arithmetic should not degrade the precision (42ns) and that means you need to be careful with the fractional part, especially if the errors with the fractional part accumulate over time (I think this was the case when I looked several years ago). That's the main reason why I did the division by 3 last, after the read, so that the precision is not impacted by the interval between two reads.
timecounter interface ensures to add the fractional ns time so it has good precision. In the table below 3600 indicates interval of 1min between two counter reads and 14400 indicates that interval of 4 minutes. Shift factor controls the ns precision we want. Considering duration of 195 years of interval between counter reads at 24mhz we get mult=83 and shift=1 which will give cycle duration = 41.5. What is the maximum duration of interval over which this read can be done in audio driver.
You also need to be careful with the multiplication factor otherwise you will exceed the 64-bit resolution. For example with the 14400 factor, you cannot handle a counter larger than 2^64/14400, which gives you 14826 hours or 1.69 years. It's one of those 'nobody will ever need more than 640KB' value. The 125 factor gives you 195 years without saturating.
Keeping maxsec at lower value will ensure good precision but the mult factor derived then might lead to overflow if the interval of counter read is big. Keeping maxsec high will reduce the mult factor and will marginally impact the precision (of the order of 6 decimal places of fraction nano second).
For 24mhz clock I am getting following scale factors at different maxsec values. I think these are as good as 125/3 125/3 gives scale factor of 41.666666666666666666666666666667
maxsec, mult, shift, scale factor (mult/(2^shift)) 0, 2796202667, 26, 41.66666667163372039794921875 3600, 87381333, 21, 41.666666507720947265625 14400, 21845333, 19, 41.6666660308837890625
I see sound driver uses only timecounter_read so conversions should be fine. If there are usages of timecounter_cyc2time then we will have to take care of updating the timecounter often as timecounter API internally counts time backwards if counter is spaced more than 1/2 the range.
Thanks Sagar
[1] http://elixir.free-electrons.com/linux/latest/source/sound/hda/hdac_stream.c...
participants (4)
-
Pierre-Louis Bossart -
Richard Cochran -
Sagar Arun Kamble -
Takashi Iwai