Introduce parity_odd() and refactor redundant parity code

[PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Kuan-Wei Chiu 8 months, 2 weeks ago

Refactor parity calculations to use the standard parity_odd() helper.
This change eliminates redundant implementations.

Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
---
 drivers/media/test-drivers/vivid/vivid-vbi-gen.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
index 70a4024d461e..5e1b7b1742e4 100644
--- a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
+++ b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
@@ -5,6 +5,7 @@
  * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
  */
 
+#include <linux/bitops.h>
 #include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/ktime.h>
@@ -165,12 +166,7 @@ static const u8 vivid_cc_sequence2[30] = {
 
 static u8 calc_parity(u8 val)
 {
-	unsigned i;
-	unsigned tot = 0;
-
-	for (i = 0; i < 7; i++)
-		tot += (val & (1 << i)) ? 1 : 0;
-	return val | ((tot & 1) ? 0 : 0x80);
+	return val | (parity_odd(val) ? 0 : 0x80);
 }
 
 static void vivid_vbi_gen_set_time_of_day(u8 *packet)
-- 
2.34.1

Re: [PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Hans Verkuil 7 months, 4 weeks ago

On 09/04/2025 17:43, Kuan-Wei Chiu wrote:
> Refactor parity calculations to use the standard parity_odd() helper.
> This change eliminates redundant implementations.
> 
> Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
> Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>

Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>

Regards,

	Hans

> ---
>  drivers/media/test-drivers/vivid/vivid-vbi-gen.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> index 70a4024d461e..5e1b7b1742e4 100644
> --- a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> +++ b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> @@ -5,6 +5,7 @@
>   * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
>   */
>  
> +#include <linux/bitops.h>
>  #include <linux/errno.h>
>  #include <linux/kernel.h>
>  #include <linux/ktime.h>
> @@ -165,12 +166,7 @@ static const u8 vivid_cc_sequence2[30] = {
>  
>  static u8 calc_parity(u8 val)
>  {
> -	unsigned i;
> -	unsigned tot = 0;
> -
> -	for (i = 0; i < 7; i++)
> -		tot += (val & (1 << i)) ? 1 : 0;
> -	return val | ((tot & 1) ? 0 : 0x80);
> +	return val | (parity_odd(val) ? 0 : 0x80);
>  }
>  
>  static void vivid_vbi_gen_set_time_of_day(u8 *packet)

Re: [PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Yury Norov 8 months, 2 weeks ago

On Wed, Apr 09, 2025 at 11:43:45PM +0800, Kuan-Wei Chiu wrote:
> Refactor parity calculations to use the standard parity_odd() helper.
> This change eliminates redundant implementations.
> 
> Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
> Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
>  drivers/media/test-drivers/vivid/vivid-vbi-gen.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> index 70a4024d461e..5e1b7b1742e4 100644
> --- a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> +++ b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> @@ -5,6 +5,7 @@
>   * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
>   */
>  
> +#include <linux/bitops.h>
>  #include <linux/errno.h>
>  #include <linux/kernel.h>
>  #include <linux/ktime.h>
> @@ -165,12 +166,7 @@ static const u8 vivid_cc_sequence2[30] = {
>  
>  static u8 calc_parity(u8 val)
>  {
> -	unsigned i;
> -	unsigned tot = 0;
> -
> -	for (i = 0; i < 7; i++)
> -		tot += (val & (1 << i)) ? 1 : 0;
> -	return val | ((tot & 1) ? 0 : 0x80);
> +	return val | (parity_odd(val) ? 0 : 0x80);

So, if val == 0 than parity_odd(val) is also 0, and this can be
simplified just to:
        return parity(val) ? 0 : 0x80;
Or I miss something?

>  }
>  
>  static void vivid_vbi_gen_set_time_of_day(u8 *packet)
> -- 
> 2.34.1

Re: [PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Kuan-Wei Chiu 8 months, 1 week ago

On Wed, Apr 09, 2025 at 01:03:42PM -0400, Yury Norov wrote:
> On Wed, Apr 09, 2025 at 11:43:45PM +0800, Kuan-Wei Chiu wrote:
> > Refactor parity calculations to use the standard parity_odd() helper.
> > This change eliminates redundant implementations.
> > 
> > Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
> > Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
> > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > ---
> >  drivers/media/test-drivers/vivid/vivid-vbi-gen.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > index 70a4024d461e..5e1b7b1742e4 100644
> > --- a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > +++ b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > @@ -5,6 +5,7 @@
> >   * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
> >   */
> >  
> > +#include <linux/bitops.h>
> >  #include <linux/errno.h>
> >  #include <linux/kernel.h>
> >  #include <linux/ktime.h>
> > @@ -165,12 +166,7 @@ static const u8 vivid_cc_sequence2[30] = {
> >  
> >  static u8 calc_parity(u8 val)
> >  {
> > -	unsigned i;
> > -	unsigned tot = 0;
> > -
> > -	for (i = 0; i < 7; i++)
> > -		tot += (val & (1 << i)) ? 1 : 0;
> > -	return val | ((tot & 1) ? 0 : 0x80);
> > +	return val | (parity_odd(val) ? 0 : 0x80);
> 
> So, if val == 0 than parity_odd(val) is also 0, and this can be
> simplified just to:
>         return parity(val) ? 0 : 0x80;
> Or I miss something?
>
If val == 0x01, the return value of calc_parity() will remain 0x01.
If changed to return parity_odd(val) ? 0 : 0x80;, the return value will
be changed to 0x00.

Regards,
Kuan-Wei

> >  }
> >  
> >  static void vivid_vbi_gen_set_time_of_day(u8 *packet)
> > -- 
> > 2.34.1

Re: [PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Yury Norov 8 months, 1 week ago

On Thu, Apr 10, 2025 at 02:23:09AM +0800, Kuan-Wei Chiu wrote:
> On Wed, Apr 09, 2025 at 01:03:42PM -0400, Yury Norov wrote:
> > On Wed, Apr 09, 2025 at 11:43:45PM +0800, Kuan-Wei Chiu wrote:
> > > Refactor parity calculations to use the standard parity_odd() helper.
> > > This change eliminates redundant implementations.
> > > 
> > > Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
> > > Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
> > > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > > ---
> > >  drivers/media/test-drivers/vivid/vivid-vbi-gen.c | 8 ++------
> > >  1 file changed, 2 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > > index 70a4024d461e..5e1b7b1742e4 100644
> > > --- a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > > +++ b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > > @@ -5,6 +5,7 @@
> > >   * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
> > >   */
> > >  
> > > +#include <linux/bitops.h>
> > >  #include <linux/errno.h>
> > >  #include <linux/kernel.h>
> > >  #include <linux/ktime.h>
> > > @@ -165,12 +166,7 @@ static const u8 vivid_cc_sequence2[30] = {
> > >  
> > >  static u8 calc_parity(u8 val)
> > >  {
> > > -	unsigned i;
> > > -	unsigned tot = 0;
> > > -
> > > -	for (i = 0; i < 7; i++)
> > > -		tot += (val & (1 << i)) ? 1 : 0;
> > > -	return val | ((tot & 1) ? 0 : 0x80);
> > > +	return val | (parity_odd(val) ? 0 : 0x80);
> > 
> > So, if val == 0 than parity_odd(val) is also 0, and this can be
> > simplified just to:
> >         return parity(val) ? 0 : 0x80;
> > Or I miss something?
> >
> If val == 0x01, the return value of calc_parity() will remain 0x01.
> If changed to return parity_odd(val) ? 0 : 0x80;, the return value will
> be changed to 0x00.

Sorry, I meant
        return val ? 0 : 0x80;

This 'val | (parity_odd(val)' is only false when val == 0, right?
When val != 0, compiler will return true immediately, not even calling
parity().

I think we need a comment from authors.

Re: [PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Kuan-Wei Chiu 8 months, 1 week ago

On Wed, Apr 09, 2025 at 02:41:03PM -0400, Yury Norov wrote:
> On Thu, Apr 10, 2025 at 02:23:09AM +0800, Kuan-Wei Chiu wrote:
> > On Wed, Apr 09, 2025 at 01:03:42PM -0400, Yury Norov wrote:
> > > On Wed, Apr 09, 2025 at 11:43:45PM +0800, Kuan-Wei Chiu wrote:
> > > > Refactor parity calculations to use the standard parity_odd() helper.
> > > > This change eliminates redundant implementations.
> > > > 
> > > > Co-developed-by: Yu-Chun Lin <eleanor15x@gmail.com>
> > > > Signed-off-by: Yu-Chun Lin <eleanor15x@gmail.com>
> > > > Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> > > > ---
> > > >  drivers/media/test-drivers/vivid/vivid-vbi-gen.c | 8 ++------
> > > >  1 file changed, 2 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > > > index 70a4024d461e..5e1b7b1742e4 100644
> > > > --- a/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > > > +++ b/drivers/media/test-drivers/vivid/vivid-vbi-gen.c
> > > > @@ -5,6 +5,7 @@
> > > >   * Copyright 2014 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
> > > >   */
> > > >  
> > > > +#include <linux/bitops.h>
> > > >  #include <linux/errno.h>
> > > >  #include <linux/kernel.h>
> > > >  #include <linux/ktime.h>
> > > > @@ -165,12 +166,7 @@ static const u8 vivid_cc_sequence2[30] = {
> > > >  
> > > >  static u8 calc_parity(u8 val)
> > > >  {
> > > > -	unsigned i;
> > > > -	unsigned tot = 0;
> > > > -
> > > > -	for (i = 0; i < 7; i++)
> > > > -		tot += (val & (1 << i)) ? 1 : 0;
> > > > -	return val | ((tot & 1) ? 0 : 0x80);
> > > > +	return val | (parity_odd(val) ? 0 : 0x80);
> > > 
> > > So, if val == 0 than parity_odd(val) is also 0, and this can be
> > > simplified just to:
> > >         return parity(val) ? 0 : 0x80;
> > > Or I miss something?
> > >
> > If val == 0x01, the return value of calc_parity() will remain 0x01.
> > If changed to return parity_odd(val) ? 0 : 0x80;, the return value will
> > be changed to 0x00.
> 
> Sorry, I meant
>         return val ? 0 : 0x80;
> 
> This 'val | (parity_odd(val)' is only false when val == 0, right?
> When val != 0, compiler will return true immediately, not even calling
> parity().
>
I'm still confused.

Maybe you're interpreting the code as:

	(val | parity(val)) ? 0 : 0x80

But what we're trying to do is:

	val | (parity(val) ? 0 : 0x80)

So, for example, if val == 0x06, the return value will be 0x86.
Only returning 0 or 0x80 seems wrong to me.
Or did I misunderstand something?

Regards,
Kuan-Wei

> I think we need a comment from authors.

Re: [PATCH v4 02/13] media: media/test_drivers: Replace open-coded parity calculation with parity_odd()

Posted by Yury Norov 8 months, 1 week ago

On Thu, Apr 10, 2025 at 02:56:41AM +0800, Kuan-Wei Chiu wrote:
> On Wed, Apr 09, 2025 at 02:41:03PM -0400, Yury Norov wrote:
> > On Thu, Apr 10, 2025 at 02:23:09AM +0800, Kuan-Wei Chiu wrote:
> > > On Wed, Apr 09, 2025 at 01:03:42PM -0400, Yury Norov wrote:
> > > > On Wed, Apr 09, 2025 at 11:43:45PM +0800, Kuan-Wei Chiu wrote:

> > > > So, if val == 0 than parity_odd(val) is also 0, and this can be
> > > > simplified just to:
> > > >         return parity(val) ? 0 : 0x80;
> > > > Or I miss something?
> > > >
> > > If val == 0x01, the return value of calc_parity() will remain 0x01.
> > > If changed to return parity_odd(val) ? 0 : 0x80;, the return value will
> > > be changed to 0x00.
> > 
> > Sorry, I meant
> >         return val ? 0 : 0x80;
> > 
> > This 'val | (parity_odd(val)' is only false when val == 0, right?
> > When val != 0, compiler will return true immediately, not even calling
> > parity().
> >
> I'm still confused.
> 
> Maybe you're interpreting the code as:
> 
> 	(val | parity(val)) ? 0 : 0x80
> 
> But what we're trying to do is:
> 
> 	val | (parity(val) ? 0 : 0x80)
> 
> So, for example, if val == 0x06, the return value will be 0x86.
> Only returning 0 or 0x80 seems wrong to me.
> Or did I misunderstand something?

I misread the whole construction. Sorry, you're right. Scratch this.