[PATCH] media: staging: rkisp1: rsz: make const array static, makes object smaller

[PATCH] media: staging: rkisp1: rsz: make const array static, makes object smaller

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

Don't populate the const array dev_names on the stack but instead it
static. Makes the object code smaller by 15 bytes.

Before:
   text	   data	    bss	    dec	    hex	filename
  17091	   2648	     64	  19803	   4d5b	media/rkisp1/rkisp1-resizer.o

After:
   text	   data	    bss	    dec	    hex	filename
  17012	   2712	     64	  19788	   4d4c	media/rkisp1/rkisp1-resizer.o

(gcc version 10.2.0)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/staging/media/rkisp1/rkisp1-resizer.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-resizer.c
index 1687d82e6c68..7ca5b47c5bf5 100644
--- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
+++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
@@ -763,8 +763,10 @@ static void rkisp1_rsz_unregister(struct rkisp1_resizer *rsz)
 
 static int rkisp1_rsz_register(struct rkisp1_resizer *rsz)
 {
-	const char * const dev_names[] = {RKISP1_RSZ_MP_DEV_NAME,
-					  RKISP1_RSZ_SP_DEV_NAME};
+	static const char * const dev_names[] = {
+		RKISP1_RSZ_MP_DEV_NAME,
+		RKISP1_RSZ_SP_DEV_NAME
+	};
 	struct media_pad *pads = rsz->pads;
 	struct v4l2_subdev *sd = &rsz->sd;
 	int ret;
-- 
2.27.0

RE: [PATCH] media: staging: rkisp1: rsz: make const array static, makes object smaller

[David Laight]

From: Colin King
> Sent: 20 October 2020 15:47
> 
> From: Colin Ian King <colin.king@canonical.com>
> 
> Don't populate the const array dev_names on the stack but instead it
> static. Makes the object code smaller by 15 bytes.
> 
> Before:
>    text	   data	    bss	    dec	    hex	filename
>   17091	   2648	     64	  19803	   4d5b	media/rkisp1/rkisp1-resizer.o
> 
> After:
>    text	   data	    bss	    dec	    hex	filename
>   17012	   2712	     64	  19788	   4d4c	media/rkisp1/rkisp1-resizer.o
> 
> (gcc version 10.2.0)
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/staging/media/rkisp1/rkisp1-resizer.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-
> resizer.c
> index 1687d82e6c68..7ca5b47c5bf5 100644
> --- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
> +++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
> @@ -763,8 +763,10 @@ static void rkisp1_rsz_unregister(struct rkisp1_resizer *rsz)
> 
>  static int rkisp1_rsz_register(struct rkisp1_resizer *rsz)
>  {
> -	const char * const dev_names[] = {RKISP1_RSZ_MP_DEV_NAME,
> -					  RKISP1_RSZ_SP_DEV_NAME};
> +	static const char * const dev_names[] = {
> +		RKISP1_RSZ_MP_DEV_NAME,
> +		RKISP1_RSZ_SP_DEV_NAME
> +	};
>  	struct media_pad *pads = rsz->pads;
>  	struct v4l2_subdev *sd = &rsz->sd;
>  	int ret;

Don't look at what that code is actually doing....
It is rather horrid.
rkisp1_rsz_register() is called for each entry in an array (twice).
The array index is written into rsz->id.
The value is then used to select one of the two strings.
But rsz->id is actually an enum type.

rkisp1_rsz_register() should probably just be called twice with some
extra parameters.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH] media: staging: rkisp1: rsz: make const array static, makes object smaller

[Dafna Hirschfeld]

Hi, thanks,

Am 20.10.20 um 16:46 schrieb Colin King:
> From: Colin Ian King <colin.king@canonical.com>
> 
> Don't populate the const array dev_names on the stack but instead it
> static. Makes the object code smaller by 15 bytes.
> 
> Before:
>     text	   data	    bss	    dec	    hex	filename
>    17091	   2648	     64	  19803	   4d5b	media/rkisp1/rkisp1-resizer.o
> 
> After:
>     text	   data	    bss	    dec	    hex	filename
>    17012	   2712	     64	  19788	   4d4c	media/rkisp1/rkisp1-resizer.o

On the other hand the data segment is 64 bytes bigger.
I don't know what is more important to save.
Anyway, the rkisp1-capture.c does the same with the names
so it is better to be consistent.

Thanks,
Dafna

> 
> (gcc version 10.2.0)
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>   drivers/staging/media/rkisp1/rkisp1-resizer.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-resizer.c
> index 1687d82e6c68..7ca5b47c5bf5 100644
> --- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
> +++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
> @@ -763,8 +763,10 @@ static void rkisp1_rsz_unregister(struct rkisp1_resizer *rsz)
>   
>   static int rkisp1_rsz_register(struct rkisp1_resizer *rsz)
>   {
> -	const char * const dev_names[] = {RKISP1_RSZ_MP_DEV_NAME,
> -					  RKISP1_RSZ_SP_DEV_NAME};
> +	static const char * const dev_names[] = {
> +		RKISP1_RSZ_MP_DEV_NAME,
> +		RKISP1_RSZ_SP_DEV_NAME
> +	};
>   	struct media_pad *pads = rsz->pads;
>   	struct v4l2_subdev *sd = &rsz->sd;
>   	int ret;
> 

Re: [PATCH] media: staging: rkisp1: rsz: make const array static, makes object smaller

[Dafna Hirschfeld]

Am 20.10.20 um 17:29 schrieb David Laight:
> From: Colin King
>> Sent: 20 October 2020 15:47
>>
>> From: Colin Ian King <colin.king@canonical.com>
>>
>> Don't populate the const array dev_names on the stack but instead it
>> static. Makes the object code smaller by 15 bytes.
>>
>> Before:
>>     text	   data	    bss	    dec	    hex	filename
>>    17091	   2648	     64	  19803	   4d5b	media/rkisp1/rkisp1-resizer.o
>>
>> After:
>>     text	   data	    bss	    dec	    hex	filename
>>    17012	   2712	     64	  19788	   4d4c	media/rkisp1/rkisp1-resizer.o
>>
>> (gcc version 10.2.0)
>>
>> Signed-off-by: Colin Ian King <colin.king@canonical.com>
>> ---
>>   drivers/staging/media/rkisp1/rkisp1-resizer.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-
>> resizer.c
>> index 1687d82e6c68..7ca5b47c5bf5 100644
>> --- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
>> +++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
>> @@ -763,8 +763,10 @@ static void rkisp1_rsz_unregister(struct rkisp1_resizer *rsz)
>>
>>   static int rkisp1_rsz_register(struct rkisp1_resizer *rsz)
>>   {
>> -	const char * const dev_names[] = {RKISP1_RSZ_MP_DEV_NAME,
>> -					  RKISP1_RSZ_SP_DEV_NAME};
>> +	static const char * const dev_names[] = {
>> +		RKISP1_RSZ_MP_DEV_NAME,
>> +		RKISP1_RSZ_SP_DEV_NAME
>> +	};
>>   	struct media_pad *pads = rsz->pads;
>>   	struct v4l2_subdev *sd = &rsz->sd;
>>   	int ret;
> 
> Don't look at what that code is actually doing....
> It is rather horrid.
> rkisp1_rsz_register() is called for each entry in an array (twice).
> The array index is written into rsz->id.
> The value is then used to select one of the two strings.
> But rsz->id is actually an enum type.

Hi,
Is it that bad to use enum as an array index?
we use it in many places in the driver.

Thanks,
Dafna

> 
> rkisp1_rsz_register() should probably just be called twice with some
> extra parameters.
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
> 

RE: [PATCH] media: staging: rkisp1: rsz: make const array static, makes object smaller

[David Laight]

From: Dafna Hirschfeld
> Sent: 20 October 2020 18:10
> 
> Am 20.10.20 um 17:29 schrieb David Laight:
> > From: Colin King
> >> Sent: 20 October 2020 15:47
> >>
> >> From: Colin Ian King <colin.king@canonical.com>
> >>
...
> >> diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-
> >> resizer.c
> >> index 1687d82e6c68..7ca5b47c5bf5 100644
> >> --- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
> >> +++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
> >> @@ -763,8 +763,10 @@ static void rkisp1_rsz_unregister(struct rkisp1_resizer *rsz)
> >>
> >>   static int rkisp1_rsz_register(struct rkisp1_resizer *rsz)
> >>   {
> >> -	const char * const dev_names[] = {RKISP1_RSZ_MP_DEV_NAME,
> >> -					  RKISP1_RSZ_SP_DEV_NAME};
> >> +	static const char * const dev_names[] = {
> >> +		RKISP1_RSZ_MP_DEV_NAME,
> >> +		RKISP1_RSZ_SP_DEV_NAME
> >> +	};
> >>   	struct media_pad *pads = rsz->pads;
> >>   	struct v4l2_subdev *sd = &rsz->sd;
> >>   	int ret;
> >
> > Don't look at what that code is actually doing....
> > It is rather horrid.
> > rkisp1_rsz_register() is called for each entry in an array (twice).
> > The array index is written into rsz->id.
> > The value is then used to select one of the two strings.
> > But rsz->id is actually an enum type.
> 
> Hi,
> Is it that bad to use enum as an array index?
> we use it in many places in the driver.

You'd normally use a constant from the enum to size the array definition.
In this case you've an enum, an array [2] and the dev_names[]
all of which have to match 'by magic'.

There is a loop that half implies you might add a third type.
but then the following code only works for the two types.
You've complex error recovery in case one of the calls to 
rkisp1_rsz_register() fails - but since there can only ever
be two calls the code could be much simpler.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)