diff mbox

[-next] drm/nouveau/clk: Use plain "/" for 32-bit division

Message ID 1423065755-19337-1-git-send-email-geert@linux-m68k.org (mailing list archive)
State New, archived
Headers show

Commit Message

Geert Uytterhoeven Feb. 4, 2015, 4:02 p.m. UTC
On 32-bit platforms using asm-generic/div64.h:

drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c: In function 'gk20a_pllg_calc_rate':
drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:79: warning: comparison of distinct pointer types lacks a cast
  do_div(rate, divider);
                                                                               ^
drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:2: warning: right shift count >= width of type
  do_div(rate, divider);
  ^
drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:238: warning: passing argument 1 of '__div64_32' from incompatible pointer type
  do_div(rate, divider);
                                                                                                                                                                                                                                              ^
In file included from arch/parisc/include/generated/asm/div64.h:1:0,
                 from include/linux/kernel.h:124,
                 from include/linux/list.h:8,
                 from include/linux/preempt.h:10,
                 from include/linux/spinlock.h:50,
                 from include/linux/mmzone.h:7,
                 from include/linux/gfp.h:5,
                 from include/linux/slab.h:14,
                 from drivers/gpu/drm/nouveau/include/nvif/os.h:5,
                 from drivers/gpu/drm/nouveau/include/nvkm/core/os.h:3,
                 from drivers/gpu/drm/nouveau/include/nvkm/core/object.h:3,
                 from drivers/gpu/drm/nouveau/include/nvkm/core/subdev.h:3,
                 from drivers/gpu/drm/nouveau/include/nvkm/subdev/clk.h:3,
                 from drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:25:
include/asm-generic/div64.h:35:17: note: expected 'uint64_t *' but argument is of type 'u32 *'
 extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
                 ^

do_div() is meant for 64-bit by 32-bit division, but both the dividend
and divisor are 32-bit here. Hence use plain "/" instead.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Compile-tested only.

parisc/allmodconfig:
http://kisskb.ellerman.id.au/kisskb/buildresult/12358386/
---
 drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

Alexandre Courbot Feb. 6, 2015, 6:50 a.m. UTC | #1
Hi Geert,

On 02/05/2015 01:02 AM, Geert Uytterhoeven wrote:
> On 32-bit platforms using asm-generic/div64.h:
>
> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c: In function 'gk20a_pllg_calc_rate':
> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:79: warning: comparison of distinct pointer types lacks a cast
>    do_div(rate, divider);
>                                                                                 ^
> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:2: warning: right shift count >= width of type
>    do_div(rate, divider);
>    ^
> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:238: warning: passing argument 1 of '__div64_32' from incompatible pointer type
>    do_div(rate, divider);
>                                                                                                                                                                                                                                                ^
> In file included from arch/parisc/include/generated/asm/div64.h:1:0,
>                   from include/linux/kernel.h:124,
>                   from include/linux/list.h:8,
>                   from include/linux/preempt.h:10,
>                   from include/linux/spinlock.h:50,
>                   from include/linux/mmzone.h:7,
>                   from include/linux/gfp.h:5,
>                   from include/linux/slab.h:14,
>                   from drivers/gpu/drm/nouveau/include/nvif/os.h:5,
>                   from drivers/gpu/drm/nouveau/include/nvkm/core/os.h:3,
>                   from drivers/gpu/drm/nouveau/include/nvkm/core/object.h:3,
>                   from drivers/gpu/drm/nouveau/include/nvkm/core/subdev.h:3,
>                   from drivers/gpu/drm/nouveau/include/nvkm/subdev/clk.h:3,
>                   from drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:25:
> include/asm-generic/div64.h:35:17: note: expected 'uint64_t *' but argument is of type 'u32 *'
>   extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
>                   ^
>
> do_div() is meant for 64-bit by 32-bit division, but both the dividend
> and divisor are 32-bit here. Hence use plain "/" instead.
>
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> Compile-tested only.
>
> parisc/allmodconfig:
> http://kisskb.ellerman.id.au/kisskb/buildresult/12358386/
> ---
>   drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
> index 65c532742b08d1c6..022595876ea4dc85 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
> @@ -144,9 +144,8 @@ gk20a_pllg_calc_rate(struct gk20a_clk_priv *priv)
>
>   	rate = priv->parent_rate * priv->n;
>   	divider = priv->m * pl_to_div[priv->pl];
> -	do_div(rate, divider);
>
> -	return rate / 2;
> +	return rate / divider / 2;

I agree there is a problem here, but considering the theoretical values 
that rate can take, could we rather fix this by making rate a u64? With 
the current maximum values of priv->parent_rate and priv->n, rate might 
approach dangerously to the u32 limit and I believe casting it to u64 
would be safer.
Geert Uytterhoeven Feb. 6, 2015, 7:53 a.m. UTC | #2
Hi Alexandre,

On Fri, Feb 6, 2015 at 7:50 AM, Alexandre Courbot <acourbot@nvidia.com> wrote:
> On 02/05/2015 01:02 AM, Geert Uytterhoeven wrote:
>> On 32-bit platforms using asm-generic/div64.h:
>> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c: In function
>> 'gk20a_pllg_calc_rate':
>> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:79: warning:
>> comparison of distinct pointer types lacks a cast
>>    do_div(rate, divider);
>>
>> ^
>> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:2: warning: right
>> shift count >= width of type
>>    do_div(rate, divider);
>>    ^
>> drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:147:238: warning: passing
>> argument 1 of '__div64_32' from incompatible pointer type
>>    do_div(rate, divider);
>>
>> ^
>> In file included from arch/parisc/include/generated/asm/div64.h:1:0,
>>                   from include/linux/kernel.h:124,
>>                   from include/linux/list.h:8,
>>                   from include/linux/preempt.h:10,
>>                   from include/linux/spinlock.h:50,
>>                   from include/linux/mmzone.h:7,
>>                   from include/linux/gfp.h:5,
>>                   from include/linux/slab.h:14,
>>                   from drivers/gpu/drm/nouveau/include/nvif/os.h:5,
>>                   from drivers/gpu/drm/nouveau/include/nvkm/core/os.h:3,
>>                   from
>> drivers/gpu/drm/nouveau/include/nvkm/core/object.h:3,
>>                   from
>> drivers/gpu/drm/nouveau/include/nvkm/core/subdev.h:3,
>>                   from
>> drivers/gpu/drm/nouveau/include/nvkm/subdev/clk.h:3,
>>                   from drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c:25:
>> include/asm-generic/div64.h:35:17: note: expected 'uint64_t *' but
>> argument is of type 'u32 *'
>>   extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
>>                   ^
>>
>> do_div() is meant for 64-bit by 32-bit division, but both the dividend
>> and divisor are 32-bit here. Hence use plain "/" instead.
>>
>> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
>> ---
>> Compile-tested only.
>>
>> parisc/allmodconfig:
>> http://kisskb.ellerman.id.au/kisskb/buildresult/12358386/
>> ---
>>   drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
>> b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
>> index 65c532742b08d1c6..022595876ea4dc85 100644
>> --- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
>> +++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
>> @@ -144,9 +144,8 @@ gk20a_pllg_calc_rate(struct gk20a_clk_priv *priv)
>>
>>         rate = priv->parent_rate * priv->n;
>>         divider = priv->m * pl_to_div[priv->pl];
>> -       do_div(rate, divider);
>>
>> -       return rate / 2;
>> +       return rate / divider / 2;
>
>
> I agree there is a problem here, but considering the theoretical values that
> rate can take, could we rather fix this by making rate a u64? With the
> current maximum values of priv->parent_rate and priv->n, rate might approach
> dangerously to the u32 limit and I believe casting it to u64 would be safer.

Yes, that's better.

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
diff mbox

Patch

diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
index 65c532742b08d1c6..022595876ea4dc85 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/clk/gk20a.c
@@ -144,9 +144,8 @@  gk20a_pllg_calc_rate(struct gk20a_clk_priv *priv)
 
 	rate = priv->parent_rate * priv->n;
 	divider = priv->m * pl_to_div[priv->pl];
-	do_div(rate, divider);
 
-	return rate / 2;
+	return rate / divider / 2;
 }
 
 static int