Implement the ffsll based on built-in function "__builtin_ffsll()"

ffsll will return one plus the index of the least significant 1-bit in
doublewords or if doublewords is zero, returns zero.

Signed-off-by: Rahul Singh <rahul.singh@arm.com>
---
Changes in V4:
 - This patch is introduce in this verison.
---
 xen/include/asm-arm/bitops.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/xen/include/asm-arm/bitops.h b/xen/include/asm-arm/bitops.h
index 71ae14cab3..7f83ee1828 100644
--- a/xen/include/asm-arm/bitops.h
+++ b/xen/include/asm-arm/bitops.h
@@ -170,6 +170,18 @@ static inline unsigned int find_first_set_bit(unsigned long word)
         return ffsl(word) - 1;
 }
 
+/**
+ * ffsll - find the first least significant set bit
+ * @doubleword: double word to search
+ *
+ * Returns one plus the index of the least significant 1-bit in @doubleword
+ * or if doubleword is zero, returns zero.
+ */
+static inline int ffsll(long long doubleword)
+{
+        return __builtin_ffsll(doubleword);
+}
+
 /**
  * hweightN - returns the hamming weight of a N-bit word
  * @x: the word to weigh
-- 
2.17.1

On Fri, 8 Jan 2021, Rahul Singh wrote:
> Implement the ffsll based on built-in function "__builtin_ffsll()"
> 
> ffsll will return one plus the index of the least significant 1-bit in
> doublewords or if doublewords is zero, returns zero.
> 
> Signed-off-by: Rahul Singh <rahul.singh@arm.com>
> ---
> Changes in V4:
>  - This patch is introduce in this verison.
> ---
>  xen/include/asm-arm/bitops.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/xen/include/asm-arm/bitops.h b/xen/include/asm-arm/bitops.h
> index 71ae14cab3..7f83ee1828 100644
> --- a/xen/include/asm-arm/bitops.h
> +++ b/xen/include/asm-arm/bitops.h
> @@ -170,6 +170,18 @@ static inline unsigned int find_first_set_bit(unsigned long word)
>          return ffsl(word) - 1;
>  }
>  
> +/**
> + * ffsll - find the first least significant set bit
> + * @doubleword: double word to search
> + *
> + * Returns one plus the index of the least significant 1-bit in @doubleword
> + * or if doubleword is zero, returns zero.
> + */
> +static inline int ffsll(long long doubleword)
> +{
> +        return __builtin_ffsll(doubleword);
> +}

This compiles fine with my old 4.9 compiler and in gitlab too, so I am
OK with this, even better because it is less code to maintain.

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

Hi,

> On 8 Jan 2021, at 14:46, Rahul Singh <Rahul.Singh@arm.com> wrote:
> 
> Implement the ffsll based on built-in function "__builtin_ffsll()"
> 
> ffsll will return one plus the index of the least significant 1-bit in
> doublewords or if doublewords is zero, returns zero.
> 
> Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

Cheers
Bertrand

> ---
> Changes in V4:
> - This patch is introduce in this verison.
> ---
> xen/include/asm-arm/bitops.h | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
> 
> diff --git a/xen/include/asm-arm/bitops.h b/xen/include/asm-arm/bitops.h
> index 71ae14cab3..7f83ee1828 100644
> --- a/xen/include/asm-arm/bitops.h
> +++ b/xen/include/asm-arm/bitops.h
> @@ -170,6 +170,18 @@ static inline unsigned int find_first_set_bit(unsigned long word)
>         return ffsl(word) - 1;
> }
> 
> +/**
> + * ffsll - find the first least significant set bit
> + * @doubleword: double word to search
> + *
> + * Returns one plus the index of the least significant 1-bit in @doubleword
> + * or if doubleword is zero, returns zero.
> + */
> +static inline int ffsll(long long doubleword)
> +{
> +        return __builtin_ffsll(doubleword);
> +}
> +
> /**
>  * hweightN - returns the hamming weight of a N-bit word
>  * @x: the word to weigh
> -- 
> 2.17.1
> 

Hi Rahul,

On 08/01/2021 14:46, Rahul Singh wrote:
> Implement the ffsll based on built-in function "__builtin_ffsll()"
> 
> ffsll will return one plus the index of the least significant 1-bit in
> doublewords or if doublewords is zero, returns zero.
> 
> Signed-off-by: Rahul Singh <rahul.singh@arm.com>
> ---
> Changes in V4:
>   - This patch is introduce in this verison.
> ---
>   xen/include/asm-arm/bitops.h | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/xen/include/asm-arm/bitops.h b/xen/include/asm-arm/bitops.h
> index 71ae14cab3..7f83ee1828 100644
> --- a/xen/include/asm-arm/bitops.h
> +++ b/xen/include/asm-arm/bitops.h
> @@ -170,6 +170,18 @@ static inline unsigned int find_first_set_bit(unsigned long word)
>           return ffsl(word) - 1;
>   }
>   
> +/**
> + * ffsll - find the first least significant set bit
> + * @doubleword: double word to search
> + *
> + * Returns one plus the index of the least significant 1-bit in @doubleword
> + * or if doubleword is zero, returns zero.
> + */
> +static inline int ffsll(long long doubleword)

If I am not mistaken, we already have an helper doing exactly the same 
(see ffs64() in xen/bitops.h).

Can you check if it is effectively the case and use it?

Cheers,

-- 
Julien Grall

Hello Julien,

> On 15 Jan 2021, at 12:16 pm, Julien Grall <julien@xen.org> wrote:
> 
> Hi Rahul,
> 
> On 08/01/2021 14:46, Rahul Singh wrote:
>> Implement the ffsll based on built-in function "__builtin_ffsll()"
>> ffsll will return one plus the index of the least significant 1-bit in
>> doublewords or if doublewords is zero, returns zero.
>> Signed-off-by: Rahul Singh <rahul.singh@arm.com>
>> ---
>> Changes in V4:
>>  - This patch is introduce in this verison.
>> ---
>>  xen/include/asm-arm/bitops.h | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>> diff --git a/xen/include/asm-arm/bitops.h b/xen/include/asm-arm/bitops.h
>> index 71ae14cab3..7f83ee1828 100644
>> --- a/xen/include/asm-arm/bitops.h
>> +++ b/xen/include/asm-arm/bitops.h
>> @@ -170,6 +170,18 @@ static inline unsigned int find_first_set_bit(unsigned long word)
>>          return ffsl(word) - 1;
>>  }
>>  +/**
>> + * ffsll - find the first least significant set bit
>> + * @doubleword: double word to search
>> + *
>> + * Returns one plus the index of the least significant 1-bit in @doubleword
>> + * or if doubleword is zero, returns zero.
>> + */
>> +static inline int ffsll(long long doubleword)
> 
> If I am not mistaken, we already have an helper doing exactly the same (see ffs64() in xen/bitops.h).
> 
> Can you check if it is effectively the case and use it?

I checked we can use the ffs64() for SMMUv3 driver as it is doing exactly the same as ffsll().
I will modify the code to use the ffs64() in place of ffsll().

Regards,
Rahul
> 
> Cheers,
> 
> -- 
> Julien Grall