[Linux-kernel-mentees] [PATCH] media: vidtv: fix build on 32bit architectures

[Linux-kernel-mentees] [PATCH] media: vidtv: fix build on 32bit architectures

[Daniel W. S. Almeida]

From: Daniel W. S. Almeida <dwlsalmeida@gmail.com>

Fix the following error for builds on 32bit architectures:

ERROR: modpost: "__udivdi3"
[drivers/media/test-drivers/vidtv/dvb-vidtv-bridge.ko] undefined!

Which is due to 64bit divisions that did not go through the helpers
in linux/math64.h

As vidtv_mux_check_mux_rate was not operational in its current form,
drop the entire function  while it is not fixed properly.

For now, call vidtv_mux_pad_with_nulls with a constant number of packets
to avoid warnings due to unused functions when building this driver.

Fixes: f90cf6079bf67988 ("media: vidtv: add a bridge driver")
Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
---
 drivers/media/test-drivers/vidtv/vidtv_mux.c  | 34 +------------------
 .../media/test-drivers/vidtv/vidtv_s302m.c    |  4 +--
 2 files changed, 3 insertions(+), 35 deletions(-)

diff --git a/drivers/media/test-drivers/vidtv/vidtv_mux.c b/drivers/media/test-drivers/vidtv/vidtv_mux.c
index 5d1a275d504b..6e402a880fdc 100644
--- a/drivers/media/test-drivers/vidtv/vidtv_mux.c
+++ b/drivers/media/test-drivers/vidtv/vidtv_mux.c
@@ -336,38 +336,6 @@ static u32 vidtv_mux_pad_with_nulls(struct vidtv_mux *m, u32 npkts)
 	return nbytes;
 }
 
-static u32 vidtv_mux_check_mux_rate(struct vidtv_mux *m)
-{
-	/*
-	 * attempt to maintain a constant mux rate, padding with null packets
-	 * if needed
-	 */
-
-	u32 nbytes = 0;  /* the number of bytes written by this function */
-
-	u64 nbytes_expected; /* the number of bytes we should have written */
-	u64 nbytes_streamed; /* the number of bytes we actually wrote */
-	u32 num_null_pkts; /* number of null packets to bridge the gap */
-
-	u64 elapsed_time_msecs = jiffies_to_usecs(m->timing.current_jiffies -
-						  m->timing.past_jiffies);
-
-	elapsed_time_msecs = min(elapsed_time_msecs, (u64)VIDTV_MAX_SLEEP_USECS / 1000);
-	nbytes_expected = div64_u64(m->mux_rate_kbytes_sec * 1000, MSEC_PER_SEC);
-	nbytes_expected *= elapsed_time_msecs;
-
-	nbytes_streamed = m->mux_buf_offset;
-
-	if (nbytes_streamed < nbytes_expected) {
-		/* can't write half a packet: roundup to a 188 multiple */
-		nbytes_expected  = roundup(nbytes_expected - nbytes_streamed, TS_PACKET_LEN);
-		num_null_pkts    = nbytes_expected / TS_PACKET_LEN;
-		nbytes          += vidtv_mux_pad_with_nulls(m, num_null_pkts);
-	}
-
-	return nbytes;
-}
-
 static void vidtv_mux_clear(struct vidtv_mux *m)
 {
 	/* clear the packets currently in the mux */
@@ -397,7 +365,7 @@ static void vidtv_mux_tick(struct work_struct *work)
 			nbytes += vidtv_mux_push_si(m);
 
 		nbytes += vidtv_mux_poll_encoders(m);
-		nbytes += vidtv_mux_check_mux_rate(m);
+		nbytes += vidtv_mux_pad_with_nulls(m, 256);
 
 		npkts = nbytes / TS_PACKET_LEN;
 
diff --git a/drivers/media/test-drivers/vidtv/vidtv_s302m.c b/drivers/media/test-drivers/vidtv/vidtv_s302m.c
index f8049cdf564a..e3290facf57b 100644
--- a/drivers/media/test-drivers/vidtv/vidtv_s302m.c
+++ b/drivers/media/test-drivers/vidtv/vidtv_s302m.c
@@ -285,12 +285,12 @@ static void vidtv_s302m_compute_pts(struct vidtv_encoder *e)
 {
 	u64 count = e->sample_count;
 	struct vidtv_access_unit *au = e->access_units;
+	u32 duration = CLOCK_UNIT_90KHZ / e->sampling_rate_hz;
 
 	while (au) {
 		count += au->num_samples;
 
-		au->pts = count *
-			  CLOCK_UNIT_90KHZ / e->sampling_rate_hz;
+		au->pts = count * duration;
 
 		au = au->next;
 	}
-- 
2.28.0

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Re: [Linux-kernel-mentees] [PATCH] media: vidtv: fix build on 32bit architectures

[Randy Dunlap]

On 9/15/20 11:05 AM, Daniel W. S. Almeida wrote:
> From: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> 
> Fix the following error for builds on 32bit architectures:
> 
> ERROR: modpost: "__udivdi3"
> [drivers/media/test-drivers/vidtv/dvb-vidtv-bridge.ko] undefined!
> 
> Which is due to 64bit divisions that did not go through the helpers
> in linux/math64.h
> 
> As vidtv_mux_check_mux_rate was not operational in its current form,
> drop the entire function  while it is not fixed properly.
> 
> For now, call vidtv_mux_pad_with_nulls with a constant number of packets
> to avoid warnings due to unused functions when building this driver.
> 
> Fixes: f90cf6079bf67988 ("media: vidtv: add a bridge driver")
> Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> ---
>  drivers/media/test-drivers/vidtv/vidtv_mux.c  | 34 +------------------
>  .../media/test-drivers/vidtv/vidtv_s302m.c    |  4 +--
>  2 files changed, 3 insertions(+), 35 deletions(-)
> 

Works for me.  Thanks.

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested


-- 
~Randy
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Re: [Linux-kernel-mentees] [PATCH] media: vidtv: fix build on 32bit architectures

[Mauro Carvalho Chehab]

Em Tue, 15 Sep 2020 15:05:09 -0300
"Daniel W. S. Almeida" <dwlsalmeida@gmail.com> escreveu:

> From: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> 
> Fix the following error for builds on 32bit architectures:
> 
> ERROR: modpost: "__udivdi3"
> [drivers/media/test-drivers/vidtv/dvb-vidtv-bridge.ko] undefined!
> 
> Which is due to 64bit divisions that did not go through the helpers
> in linux/math64.h
> 
> As vidtv_mux_check_mux_rate was not operational in its current form,
> drop the entire function  while it is not fixed properly.
> 
> For now, call vidtv_mux_pad_with_nulls with a constant number of packets
> to avoid warnings due to unused functions when building this driver.
> 
> Fixes: f90cf6079bf67988 ("media: vidtv: add a bridge driver")
> Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> ---
>  drivers/media/test-drivers/vidtv/vidtv_mux.c  | 34 +------------------
>  .../media/test-drivers/vidtv/vidtv_s302m.c    |  4 +--
>  2 files changed, 3 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/media/test-drivers/vidtv/vidtv_mux.c b/drivers/media/test-drivers/vidtv/vidtv_mux.c
> index 5d1a275d504b..6e402a880fdc 100644
> --- a/drivers/media/test-drivers/vidtv/vidtv_mux.c
> +++ b/drivers/media/test-drivers/vidtv/vidtv_mux.c
> @@ -336,38 +336,6 @@ static u32 vidtv_mux_pad_with_nulls(struct vidtv_mux *m, u32 npkts)
>  	return nbytes;
>  }
>  
> -static u32 vidtv_mux_check_mux_rate(struct vidtv_mux *m)
> -{
> -	/*
> -	 * attempt to maintain a constant mux rate, padding with null packets
> -	 * if needed
> -	 */
> -
> -	u32 nbytes = 0;  /* the number of bytes written by this function */
> -
> -	u64 nbytes_expected; /* the number of bytes we should have written */
> -	u64 nbytes_streamed; /* the number of bytes we actually wrote */
> -	u32 num_null_pkts; /* number of null packets to bridge the gap */
> -
> -	u64 elapsed_time_msecs = jiffies_to_usecs(m->timing.current_jiffies -
> -						  m->timing.past_jiffies);
> -
> -	elapsed_time_msecs = min(elapsed_time_msecs, (u64)VIDTV_MAX_SLEEP_USECS / 1000);
> -	nbytes_expected = div64_u64(m->mux_rate_kbytes_sec * 1000, MSEC_PER_SEC);
> -	nbytes_expected *= elapsed_time_msecs;
> -
> -	nbytes_streamed = m->mux_buf_offset;
> -
> -	if (nbytes_streamed < nbytes_expected) {
> -		/* can't write half a packet: roundup to a 188 multiple */
> -		nbytes_expected  = roundup(nbytes_expected - nbytes_streamed, TS_PACKET_LEN);
> -		num_null_pkts    = nbytes_expected / TS_PACKET_LEN;
> -		nbytes          += vidtv_mux_pad_with_nulls(m, num_null_pkts);
> -	}
> -
> -	return nbytes;
> -}
> -
>  static void vidtv_mux_clear(struct vidtv_mux *m)
>  {
>  	/* clear the packets currently in the mux */
> @@ -397,7 +365,7 @@ static void vidtv_mux_tick(struct work_struct *work)
>  			nbytes += vidtv_mux_push_si(m);
>  
>  		nbytes += vidtv_mux_poll_encoders(m);
> -		nbytes += vidtv_mux_check_mux_rate(m);
> +		nbytes += vidtv_mux_pad_with_nulls(m, 256);
>  
>  		npkts = nbytes / TS_PACKET_LEN;
>  
> diff --git a/drivers/media/test-drivers/vidtv/vidtv_s302m.c b/drivers/media/test-drivers/vidtv/vidtv_s302m.c
> index f8049cdf564a..e3290facf57b 100644
> --- a/drivers/media/test-drivers/vidtv/vidtv_s302m.c
> +++ b/drivers/media/test-drivers/vidtv/vidtv_s302m.c
> @@ -285,12 +285,12 @@ static void vidtv_s302m_compute_pts(struct vidtv_encoder *e)
>  {
>  	u64 count = e->sample_count;
>  	struct vidtv_access_unit *au = e->access_units;
> +	u32 duration = CLOCK_UNIT_90KHZ / e->sampling_rate_hz;
>  
>  	while (au) {
>  		count += au->num_samples;
>  
> -		au->pts = count *
> -			  CLOCK_UNIT_90KHZ / e->sampling_rate_hz;
> +		au->pts = count * duration;

That doesn't seem to be the right thing to do here. 

Assuming that sampling rate is 48 kHz, you'll
have duration = 1.875, which would be rounded to 1.

In other words, the above is identical to:

	au->pts = count

Now, I don't know from where that CLOCK_UNIT_90KHZ came from.

If such constant is not needed anymore, just drop it. 
	
If, on the other hand, this is required by the specs, then
you may need to do a 64 bits division, e. g. using
div64_u64() or do_div().

Thanks,
Mauro
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Re: [Linux-kernel-mentees] [PATCH] media: vidtv: fix build on 32bit architectures

[Geert Uytterhoeven]

Hi Mauro, Daniel,

On Wed, Sep 16, 2020 at 8:40 AM Mauro Carvalho Chehab
<mchehab@kernel.org> wrote:
> Em Tue, 15 Sep 2020 15:05:09 -0300
> "Daniel W. S. Almeida" <dwlsalmeida@gmail.com> escreveu:
> > From: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
> >
> > Fix the following error for builds on 32bit architectures:
> >
> > ERROR: modpost: "__udivdi3"
> > [drivers/media/test-drivers/vidtv/dvb-vidtv-bridge.ko] undefined!
> >
> > Which is due to 64bit divisions that did not go through the helpers
> > in linux/math64.h
> >
> > As vidtv_mux_check_mux_rate was not operational in its current form,
> > drop the entire function  while it is not fixed properly.
> >
> > For now, call vidtv_mux_pad_with_nulls with a constant number of packets
> > to avoid warnings due to unused functions when building this driver.
> >
> > Fixes: f90cf6079bf67988 ("media: vidtv: add a bridge driver")
> > Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> # build-tested

> > --- a/drivers/media/test-drivers/vidtv/vidtv_s302m.c
> > +++ b/drivers/media/test-drivers/vidtv/vidtv_s302m.c
> > @@ -285,12 +285,12 @@ static void vidtv_s302m_compute_pts(struct vidtv_encoder *e)
> >  {
> >       u64 count = e->sample_count;
> >       struct vidtv_access_unit *au = e->access_units;
> > +     u32 duration = CLOCK_UNIT_90KHZ / e->sampling_rate_hz;
> >
> >       while (au) {
> >               count += au->num_samples;
> >
> > -             au->pts = count *
> > -                       CLOCK_UNIT_90KHZ / e->sampling_rate_hz;
> > +             au->pts = count * duration;
>
> That doesn't seem to be the right thing to do here.
>
> Assuming that sampling rate is 48 kHz, you'll
> have duration = 1.875, which would be rounded to 1.
>
> In other words, the above is identical to:
>
>         au->pts = count
>
> Now, I don't know from where that CLOCK_UNIT_90KHZ came from.
>
> If such constant is not needed anymore, just drop it.
>
> If, on the other hand, this is required by the specs, then
> you may need to do a 64 bits division, e. g. using
> div64_u64() or do_div().

As vidtv_encoder.sampling_rate_hz is u32, there's fortunately no need
to use div64_u64() (64-by-64), so div_u64() (64-by-32) is fine.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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Re: [Linux-kernel-mentees] [PATCH] media: vidtv: fix build on 32bit architectures

[Daniel W. S. Almeida]

Hi Mauro, Geert,

> That doesn't seem to be the right thing to do here.
>
> Assuming that sampling rate is 48 kHz, you'll
> have duration = 1.875, which would be rounded to 1.
>
> In other words, the above is identical to:
>
> au->pts = count
>
> Now, I don't know from where that CLOCK_UNIT_90KHZ came from.
>

Mauro, here's my current understanding:

The values for PTS have to be defined in terms of a 90khz clock. 

So for 30fps video, the values for PTS per frame would be:

frame_num/30 * 90000

so 0, 3000, 6000, 9000...etc

The same math is being used here for audio, but instead we have the
total audio sample count and a 48000 samples/sec


I did miss this rounding error though, I'm sorry.



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